perf(harness): close page on error + MD040 fence + CHANGELOG (CodeRabbit)

- frameTimeOnce now closes its page in a finally, so a failing run doesn't leak
  the page until the final browser.close() (CodeRabbit).
- fenced code block gets a bash language hint (MD040).
- CHANGELOG mentions the new --song frame-time mode.

.github/workflows/ci.yml

@@ -123,3 +123,28 @@ jobs:
               sys.exit(1)
           print(f"Validated {len(manifests)} manifest(s) — OK")
           EOF
+
+  lint:
+    # Maintainer/CI-only size + module-hygiene gate (constitution Principle I:
+    # dev tooling, never on the serve/Docker path — same category as
+    # scripts/build-tailwind.sh). max-lines WARNS (the 1,500-line size ratchet;
+    # non-blocking), while import-x/no-unresolved + no-cycle HARD-ERROR on the
+    # ES-module graphs the refactor produces. Exemptions: docs/size-exemptions.md.
+    name: lint
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        # npm ci runs third-party postinstall scripts; don't leave the token in
+        # git config for them (this job never pushes).
+        with:
+          persist-credentials: false
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: ESLint (size norm + module hygiene)
+        run: npm run lint

.specify/memory/constitution.md

@@ -48,11 +48,30 @@ output is committed, so Docker / desktop / end users never build. New
 features extend `app.js` and the existing globals (`window.playSong`,
 `window.showScreen`, `window.createHighway`, `window.feedBack`).
 
+Native ES modules are a first-class, build-free extension mechanism.
+Because `<script type="module">` and `import` are browser features — not
+a bundler — a large source file MAY be split into an `import`-ed module
+graph of plain source files, with **no build step and no framework**. A
+plugin opts in with `"scriptType": "module"` in `plugin.json`: its
+`screen.js` becomes a one-line `import './src/main.js'`, and the host
+serves the `src/` subtree from the sandboxed `/api/plugins/<id>/src/…`
+route and injects the entry as `<script type="module">`. The classic
+global-scope `screen.js` path remains fully supported; both coexist, and
+module scripts are still source-served — the no-bundler, no-transpiler,
+build-free-at-serve rule is unchanged. Core's own `static/` tree may
+migrate to the same module-graph shape (`static/js/…`) over time under
+this rule.
+
 **Non-negotiable rules**
 
 - Do not introduce a frontend framework, JSX, or a JS build pipeline in
   core. Plugins MAY ship their own bundled assets but core MUST remain
   source-served.
+- ES-module plugins remain source-served: no bundler or transpiler, and
+  their own asset URLs (worklets, WASM, images) resolve via
+  `import.meta.url` — never `document.currentScript`, which is `null`
+  inside a module. `scriptType:"module"` and the optional `minHost`
+  version floor are the only new `plugin.json` keys the module path adds.
 - Because the core Tailwind stylesheet is prebuilt, it contains only the
   classes present in core source at build time. Core's committed
   `static/tailwind.min.css` MUST stay in sync with source — CI enforces
@@ -214,6 +233,15 @@ no `..`, no absolute paths).
   runs first). Plugins MUST tolerate dependent globals being absent
   at load time and check at runtime
   (`typeof window.X === 'function'`).
+- **Module load contract**: a `scriptType:"module"` plugin is injected
+  as `<script type="module">`, whose load event fires only after its
+  whole static-import graph fetches and evaluates — so the loader's
+  completion-by-`onload` guarantee (and the `playSong` wrapper-chain
+  order above) is preserved exactly. The host loads `screen.js` once per
+  version and `showScreen` re-injects nothing, so a plugin's per-visit
+  re-initialization comes from its `screen:changed` handler, not from
+  screen.js re-running; ES-module plugins inherit this unchanged (module
+  top-level code does not re-execute on same-version re-mount).
 
 ## Development Workflow
 
@@ -256,4 +284,4 @@ no `..`, no absolute paths).
   higher-numbered principle's escape hatch is to live in a plugin
   with its own bundled assets.
 
-**Version**: 1.1.0 | **Ratified**: 2026-05-09 | **Last Amended**: 2026-06-01
+**Version**: 1.2.0 | **Ratified**: 2026-05-09 | **Last Amended**: 2026-07-08

CHANGELOG.md

@@ -7,7 +7,87 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+- **The packaged desktop app could not start (`ModuleNotFoundError: No module named
+  'appstate'`).** feedback-desktop's `scripts/bundle-slopsmith.sh` copies a *hardcoded
+  list* of core files into the app bundle — `server.py`, `VERSION`, `lib/`, `data/`,
+  `static/`, `plugins/__init__.py`. The root-level `appstate.py` and `routers/` added in
+  R3 shipped correctly in Docker and passed every test, and were then silently dropped
+  from the packaged app, which died at startup. Both now live under **`lib/`** — the one
+  core directory the Dockerfile (`COPY lib/`), `docker-compose.yml`, and the desktop
+  bundler (`cp -r lib`) all copy wholesale, and that all three put on `sys.path` (on
+  Windows via the embeddable-Python `._pth`, where `PYTHONPATH` is ignored). This needs no
+  change in feedback-desktop and no new release to take effect. Placing them there is also
+  correct under Principle V: with the injection seam, `appstate.py` constructs nothing and
+  does no import-time IO, and a route module only builds an `APIRouter`. The
+  `Dockerfile` / `.dockerignore` / `docker-compose.yml` entries added for the root layout
+  are reverted. New `tests/test_packaging.py` walks `server.py`'s module-level imports and
+  fails if any first-party module resolves outside a directory the packagers copy, so the
+  next root-level module can't ship broken.
+
 ### Added
+- **Perf harness now measures 2D-highway frame time (R3c gate).** `scripts/perf-baseline.mjs` gains a `--song` mode that reports per-frame draw-cost p50/p95/p99 (draw-tagged via `highway.addDrawHook`), the metric that gates the `highway.js` split. Maintainer/CI-only; baseline recorded in `docs/perf-baseline.md`.
+- **`routers/` — extracting `server.py`'s route layer, cheapest-first (R3).** Each PR moves a cohesive route group into a `fastapi.APIRouter` under `lib/routers/`, mounted with `app.include_router(...)` at its original site (FastAPI matches in registration order; the full route table stays byte-identical). Bodies are verbatim — only the decorator receiver (`@app` → `@router`) and singleton reads (`meta_db` → `appstate.meta_db`, resolved at call time) change. So far: `audio_effects` (5), `artist_aliases` (5), `loops` (3), `playlists` (12 + covers), `ws_highway` (the 902-line highway chart WebSocket), `chart` (split/unsplit/work/fileinfo — unblocked by the DLC-path substrate). The DLC library-path resolution (`_get_dlc_dir`, pure `_resolve_dlc_path`) moved to `lib/dlc_paths.py`, reading paths through the seam; `config_dir`/`dlc_dir`/`dlc_dir_env` now ride the `appstate` seam (env-derived, so the pop-and-reimport fixtures reconfigure it for free), and the shared request-field sanitizer `_clean_str` moved to `lib/reqfields.py`. The next cut is picked by a dependency-closure scan that ranks groups by how many `monkeypatch.setattr(server, …)` targets they'd drag along.
+- **`routers/` — the first extracted route module (R3).** The five audio-effects mapping
+  endpoints move out of `server.py` into `lib/routers/audio_effects.py` as a
+  `fastapi.APIRouter`, mounted with `app.include_router(...)` **at the point in the file
+  where they used to be defined** — FastAPI matches routes in registration order, so the
+  mount site preserves it. Verified: the full 143-route table (paths, methods, *and*
+  order) is byte-for-byte identical to `main`. Bodies are verbatim; the only edits are
+  the decorator receiver (`@app.get` → `@router.get`) and the singleton read
+  (`audio_effect_mappings` → `appstate.audio_effect_mappings`, a module attribute
+  resolved at call time). This proves the seam from #833 under a real consumer, including
+  the second slot. The `_demo_mode_guard` middleware still blocks all four moved write
+  routes with 403, and `Query(...)` validation still 422s — both checked against a running
+  server. `server.py`: **9,445 → 9,386 lines**.
+- **`appstate.py` — the router seam (R3).** Route modules moving out of `server.py`
+  need `meta_db` and friends but must not `import server`, or the import graph goes
+  circular the moment `server` imports them back. So `server.py` keeps *constructing*
+  its singletons and now **injects** them once — `appstate.configure(meta_db=…,
+  audio_effect_mappings=…)` — and a router reads them back as module attributes at call
+  time (`import appstate; appstate.meta_db.…`). This is the Python analogue of the
+  frontend refactor's injected `configureX({…})` seams and of the plugin
+  `setup(app, context)` contract: dependencies flow one way, `server → routers →
+  appstate`. Two properties are load-bearing and pinned by `tests/test_appstate.py`:
+  (1) `import appstate` constructs nothing and touches no disk, so the ~49 test fixtures
+  that `sys.modules.pop("server")` + re-import (to rebuild `meta_db` under a patched
+  `CONFIG_DIR`) keep working untouched — a singleton *owned* by `appstate` would survive
+  that pop and go stale; (2) reads must be late-bound (`appstate.meta_db`, never
+  `from appstate import meta_db`), since a `from` import freezes the binding and defeats
+  both a later `configure()` and `monkeypatch.setattr` — the same read-only-binding trap
+  as ES `import`. `configure()` rejects an unknown slot rather than silently creating a
+  global nothing reads, and the suite asserts `server` actually calls it (a seam whose
+  wiring can no-op undetected is worse than no seam). Lives at `lib/appstate.py`.
+
+### Changed
+- **`AudioEffectsMappingDB` moved out of `server.py` into `lib/audio_effects_db.py`
+  (R3, move-only).** The core-owned song/tone → provider routing index follows
+  `MetadataDB` out of the host file, byte-identical apart from the same constructor
+  seam (`__init__` takes `config_dir`; `audio_effect_mappings = AudioEffectsMappingDB(CONFIG_DIR)`),
+  so the module does no IO at import. The singleton stays in `server.py`; no route,
+  no test and no `monkeypatch.setattr(server, …)` target moves. `server.py`:
+  **9,705 → 9,433 lines**.
+- **`MetadataDB` moved out of `server.py` into `lib/metadata_db.py` (R3, move-only).**
+  The library metadata cache — the `MetadataDB` class (4,018 lines) plus the query
+  helpers it owns (keyset paging cursors, the tuning grouping key, smart-arrangement
+  naming, tag normalisation, the startup DB-restore swap) — now lives in its own flat
+  `lib/` module. `server.py` drops from **14,037 → 9,705 lines** and keeps the
+  `meta_db` singleton, so `server.meta_db` and `server.app` resolve exactly as before
+  and every route is untouched. The only non-verbatim change is the seam that lets the
+  class leave `server.py`: `MetadataDB.__init__` now takes `config_dir` explicitly
+  (`meta_db = MetadataDB(CONFIG_DIR)`) instead of reading the module-level `CONFIG_DIR`,
+  which also means `lib/metadata_db.py` performs no IO at import (Principle V). Logging
+  still goes through the `feedBack.server` logger, so existing log filters and `caplog`
+  assertions resolve to the same logger object. `tests/test_settings_export_library_db.py`
+  now imports `_apply_pending_db_restore` from `metadata_db` (the test moved with its
+  subject); no other test changed. Every moved block is byte-identical to its
+  `server.py` original.
+
+### Added
+- **Plugins can ship an ES-module `src/` tree (module-migration rails, R0).** The host gains three things so a plugin can move off a single global-scope `screen.js` IIFE onto native ES modules with **no build step**: (1) a new sandboxed `GET /api/plugins/{id}/src/{path}` route that serves a plugin's `src/` source subtree, containment-checked by the same `safe_join` guard as `assets/` (traversal/absolute/NUL → 404); (2) the live-edit cache contract — `Cache-Control: no-cache` + a weak mtime/size `ETag` + `If-None-Match`→`304` — applied to `src/`, `screen.js`, and `assets/` (previously `screen.js` sent no cache headers and `assets/` emitted an ETag but never revalidated), so an edited module reloads on refresh while unchanged ones `304`; and (3) `scriptType`/`minHost` passthrough from `plugin.json` to `/api/plugins`, with the loader injecting a plugin that declares `"scriptType":"module"` as `<script type="module">` (its screen.js becomes `import './src/main.js'`). A `<script type=module>` fires its load event only after its whole static-import graph evaluates, preserving the loader's completion-by-`onload` + `_loadingPluginId` contract. Classic plugins are unaffected; `minHost` is passthrough-only for now (enforcement deferred). Tests: `tests/test_plugin_src_route.py` (serve/media-type/traversal/304/no-stale-304/screen.js+assets conditional), `tests/js/plugin_loader_script_type.test.js` (guarded module injection).
+- **Module-migration governance & rails (R0).** Constitution amended to **v1.2.0**: Principle II now names native ES modules as a first-class, *build-free* extension mechanism (the `scriptType:"module"` load path, both plugins and — over time — core's `static/js/`), keeping the no-bundler/no-transpiler/source-served rule intact; Operating Constraints gains a "Module load contract" clause (a `<script type=module>` load event awaits the whole static-import graph, so completion-by-`onload` is preserved; per-visit re-init comes from the `screen:changed` event, not screen.js re-execution). Mirrored into `CLAUDE.md`. New `docs/plugin-modules.md` (the migration playbook — layering, import-time purity, `import.meta.url` assets, the ETag live-edit loop) and `docs/size-exemptions.md` (the signed 1,500-line size-norm register; Byron signs core/bundled rows, Christian the authored virtuoso row). Adds a **maintainer/CI-only** ESLint gate (`eslint.config.js` + a `lint` CI job): `max-lines` warns at 1,500 as a non-blocking ratchet (ceilings for exempt files mirror the register), and `import-x/no-unresolved` + `import-x/no-cycle` hard-error on ES-module graphs — dormant until module code lands, never on the serve/Docker path.
+- **Perf-baseline harness (R0).** `scripts/perf-baseline.mjs` (maintainer-only, Playwright-driven) captures server p50/p95/p99 latency, cold boot-to-interactive, JS-heap after an idle soak, and the injected plugin-script shape (how many are `type=module`), so every refactor phase can be checked for "screen-entry and frame-time no worse." Methodology + the R0 baseline live in `docs/perf-baseline.md`; playback frame-time and chart-loaded screen-entry rows need a seeded library and are re-taken per environment.
+- **Sort and filter the library by your personal difficulty rating — now visible at a glance, not just in the edit drawer.** `song_user_meta.user_difficulty` (the 1–5 planning rating, settable manually or seeded by a plugin like the community `difficulty_tagger`) already existed but was only readable by opening a song's per-song details drawer. The library API gains `sort=difficulty` / `sort=difficulty-desc` — a correlated subquery over `song_user_meta`, following the same unrated-rows-sort-to-the-bottom-in-both-directions pattern as the existing `mastery` sort — and library cards now show the rating as a `◆N` badge (v2 grid/tree views and the v3 grid alike), next to the tuning and lyrics badges. The classic tree view's `query_artists` batch-attaches `user_difficulty` the same way `query_page` already did for the grid, so the badge actually renders there too instead of staying dark. Tests: `tests/test_library_filters.py::test_difficulty_sort_pushes_unrated_to_bottom`, `tests/test_library_filters.py::test_tree_view_songs_carry_user_difficulty`.
 - **`lib/midi_import.py`: `convert_midi_tempo_map` — MIDI imports can finally carry
   their bars.** The keys/drums note converters always computed a tempo-aware
   tick→seconds map internally (to bake note times to absolute seconds) and then threw
@@ -29,6 +109,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **Auto-sync: DTW step constraint — riff-based songs no longer produce garbage sync points.** `librosa.sequence.dtw`'s default step pattern allows unbounded horizontal/vertical path runs, and on music with long self-similar chroma stretches (riff-driven stoner/doom, drone sections) the flat cost surface let the warping path collapse — minutes of score mapped onto a single audio frame, so the per-bar warp imported charts wildly out of sync while reporting success (observed on a real 138 BPM tab: effective displayed tempo 159 BPM, three sync points sharing one audio timestamp). `_dtw_align` now uses the standard music-sync slope-constrained step pattern (`[[1,1],[1,2],[2,1]]`, local tempo ratio bounded to 0.5x–2x), which makes the degenerate path impossible, with a fallback to unconstrained steps when the global length ratio makes the constrained pattern infeasible (e.g. a tab aligned against a full-concert video). Validated on the failing song: coarse points track the recording 1:1, refined downbeats land on onset peaks at 3.3x background energy.
 
 ### Added
+- **3D Keys Highway: key layout modes, lane-color opacity & octave lines.** A new **Highway layout** settings section rebuilds how sharps/flats and lanes draw on the 3D piano highway. **Sharps & flats layout** (`keys3d_bg_sharpMode`) picks between **floating** (the original raised-sharp look), **flat** (one plane, zero-overlap piano-shaped tiled lanes with the naturals evened out), and **realistic** (one plane, bars sized like the physical keys) — default **realistic**; the geometry lives in pure, unit-tested `laneSpanFlat()`/`laneSpanReal()` helpers. **Lane color opacity** (`keys3d_bg_laneOpacity`, 0–1, default 0) fades the pitch-class lane tint from full vivid color down to a dark floor with guide lines only at the key-block boundaries (E→F and each octave); the lane strips, per-lane separators and block lines crossfade with the value. **Octave separators** (`keys3d_bg_octaveGaps`, default on) and **Octave line contrast** (`keys3d_bg_octaveContrast`, 0–1) control the B→C octave divider, which auto-shifts from a dark to a bright layer as lane opacity fades. Settings re-read on init and apply on the next chart build. `plugins/keys_highway_3d` → 0.2.0. Tests: `plugins/keys_highway_3d/tests/fx_settings.test.js` (new defaults, sharp-mode setting, lane-geometry tiling/evening for flat, uniform/overlap for realistic, and an active-range boundary case where a white key's edge stays untrimmed when its neighboring sharp falls outside the active range).
+- **Unmapped-percussion capture now records velocities alongside times.** Both drum converters' opt-in `out_unmapped` reporting (`lib/midi_import.py` `convert_drum_track_from_midi`, `lib/gp2rs.py` `convert_drum_track_to_drumtab`) gain an index-aligned `velocities` list next to `times`, carrying each dropped note's real dynamics (MIDI velocity verbatim; GP velocity with the same 1–127 gate as mapped hits, falling back to the 100 import default). This lets a hand-mapping UI (the editor's unmapped-notes dialog) restore mapped notes at their source dynamics instead of flattening everything to `v:100`. The GP path's chronological sort now reorders times and velocities in lockstep so multi-voice measures can't silently reassign dynamics. Additive — callers that ignore the new key are unaffected. Tests: `tests/test_midi_import_drums.py`, `tests/test_gp2rs_drums.py`.
 - **Handedness (left-handed) is now a first-class choice in the instrument selector — and surfaced during onboarding.** Left-handed players could already mirror the highway, but only via a buried Settings toggle they had to find *after* setup — so a lefty hit the tour, the tuner and calibration all right-handed first. The v3 instrument badge popover now has a **Handedness: Right / Left** row alongside Instrument / Strings / Tuning (all player-orientation choices), writing the same `lefty` preference (`highway.setLefty` when a live highway exists, else the `lefty` localStorage key it reads on init; the Settings checkbox stays in sync). The first-run tour's "Choose your instrument" step — which runs **before** the tuner/audio-calibration steps — now calls it out so lefties flip it up front. Frontend-only, additive: `static/v3/badges.js`, `static/v3/onboarding-tour.js`. Tests: `tests/js/badges_handedness.test.js`.
 - **"Colorblind (deuteranope)" highway string-color preset.** Adds a one-click preset to the shared "Highway String Colors" picker, sitting next to the existing Okabe–Ito "Colorblind-friendly" preset — contributed by a deuteranopic player who found the Okabe–Ito set still hard to separate. It retunes the six main strings (red / yellow-green / blue / orange / teal / deep-purple) and keeps that set's 7/8-string colors, and applies to **both** the 2D and 3D highways via the shared picker. Frontend-only, additive: `static/app.js` (`HWC_PRESETS`).
 - **`lib/gp_autosync.py`: piecewise time-warp helpers + a working `refine_sync()`.** `auto_sync()` has always computed per-bar sync points (DTW), but consumers could only apply the scalar bar-1 `audio_offset`, so any tempo difference between the recording and the tab's authored tempo accumulated audibly over the song. New librosa-free helpers expose the full mapping: `bar_start_times(gp_path)` (per-bar score times on the same axis as the sync points — GPIF bar-resolution map for `.gp`/`.gpx`, per-tick integration for GP3/4/5), `build_warp_anchors(points, bar_starts)` (strictly-monotonic `(score, audio)` anchor pairs), `warp_time(t, anchors)` (piecewise-linear map with edge-slope extrapolation for count-ins/tails), `warp_song_times(song, warp)` (retimes a `lib.song.Song` in place: notes + sustains, chords, beats, sections, anchors, handshapes, per-phrase difficulty levels, tone changes, tempo overrides), and `gp_has_expandable_repeats(gp_path)` (detects GP3/4/5 repeat/volta/direction markup whose playback expansion the as-written sync points cannot map — callers fall back to offset-only sync). Also implements `refine_sync()`, which the editor plugin's refine-sync endpoint has imported since the snapshot but which never existed in core (the Refine button 500'd): it densifies the coarse DTW points to every Nth bar and re-times each with a local onset phase sweep (sweep radius clamped under half a beat so periodic material can't lock a full beat off; short scoring grid + median residual snap). Synthetic click-track validation: ~13ms mean / ~40ms max error from ±180ms coarse input across 117–123 BPM recordings of a 120 BPM tab. Tests: `tests/test_gp_autosync_warp.py`.

CLAUDE.md

@@ -117,6 +117,8 @@ Notes:
 
 **Frontend scripts** — `screen.js` runs in the global scope via a `<script>` tag. It can access `window.playSong`, `window.showScreen`, `window.createHighway`, the `<audio>` element, and the `window.feedBack` event emitter.
 
+**ES-module plugins (`scriptType:"module"`)** — a plugin may instead ship a native ES-module graph with **no build step**: set `"scriptType": "module"` in `plugin.json`, make `screen.js` a one-line `import './src/main.js'`, and put the module tree under `src/` (served by the sandboxed `/api/plugins/<id>/src/{path}` route). The host injects it as `<script type="module">`, whose `onload` fires only after the whole static-import graph evaluates — so the loader's completion-by-`onload` + `_loadingPluginId` + `playSong` wrapper-chain ordering all hold. Resolve your own asset URLs (worklets, WASM) with `import.meta.url` — `document.currentScript` is `null` in a module. Module top-level code does **not** re-run when the user re-enters the screen at the same version (the host loads screen.js once and `showScreen` re-injects nothing), so keep per-visit re-init in a `screen:changed` handler, exactly as classic plugins do. Classic global-scope `screen.js` remains fully supported. See `docs/plugin-modules.md`.
+
 **The playSong wrapper chain** — Plugins commonly wrap `window.playSong` to hook into song playback. Plugins load alphabetically, so the last-loaded (alphabetically later) wrapper runs first, while the alphabetically first plugin runs closest to the original. Be aware that `await` calls in inner wrappers yield to the event loop — WebSocket messages can arrive before outer wrappers finish setup.
 
 ## Plugin Best Practices

docs/perf-baseline.md

@@ -0,0 +1,92 @@
+# Perf baseline — module-migration refactor
+
+The refactor promises "measured runtime wins, no hand-waved perf claims" and
+"screen-entry and frame-time no worse." This is the baseline to hold it to.
+Rerun the harness after every phase (R0 → R3c) and compare.
+
+## Running it
+
+```
+# 1. start core against a library with real charts (see caveat below)
+CONFIG_DIR=… DLC_DIR=/path/to/songs PYTHONPATH=lib \
+  python3 -m uvicorn server:app --host 127.0.0.1 --port 8000
+
+# 2. capture (maintainer/CI-only; uses the committed Playwright chromium)
+node scripts/perf-baseline.mjs --base http://127.0.0.1:8000 --n 60 --soak 30
+```
+
+The script prints a markdown block; paste it under "Results" below with the date
+and the commit it was taken at.
+
+## What it measures
+
+- **Server latency** — p50/p95/p99 over N requests for `/api/version`,
+  `/api/plugins`, `/api/library`, `/api/library/artists`.
+- **Cold boot → interactive** — full page load to `networkidle`.
+- **JS heap** — `performance.memory.usedJSHeapSize` after load and after an idle
+  soak (a leak signal across a session).
+- **Plugin-script shape** — how many plugin `<script>`s the loader injected (a
+  "the app booted with its plugins" sanity signal).
+
+**Not yet captured — needs a seeded library with charts** (fill in when run
+against a real environment): playback **frame-time p95** on the 2D and 3D
+highway, and **screen-entry** (plugin inject → interactive) for
+editor / notedetect / highway_3d with a chart loaded. These are the
+perf-sensitive numbers that gate the `highway.js` split (R3c); the harness has
+the hooks, they just need real songs in `DLC_DIR`.
+
+## Results
+
+### R3c pre-lift baseline — 2026-07-10 (2D highway draw cost)
+
+The gate for the `highway.js` split. Captured on a seeded library (the 33 MB
+Arcturus feedpak) with the new `--song` mode, which measures **per-frame draw
+cost** — rAF callbacks are tagged via `highway.addDrawHook`, so only frames the
+highway actually painted count (the other ~half are cheap no-op loops that would
+otherwise mask a regression). Any `highway.js` change must re-run this on the
+same machine and stay within noise of these numbers.
+
+```bash
+node scripts/perf-baseline.mjs --base http://127.0.0.1:8300 \
+    --song "Arcturus - The Sham Mirrors - Kinetic.feedpak"
+```
+
+| run | draw frames | p50 | p95 | p99 | max |
+|---|---|---|---|---|---|
+| 1 | 53/106 | 2.2 | 3.2 | 3.6 | 3.6 |
+| 2 | 50/100 | 2.2 | 2.9 | 3.2 | 3.2 |
+| 3 | 53/106 | 2.1 | 2.7 | 3.5 | 3.5 |
+
+**p50 ≈ 2.2 ms · p95 spread 2.7–3.2 ms** (3 runs × 10 s playback, headless
+chromium on the dev box). The `H`-container lift changes each closure-slot read
+to a `H.<slot>` property load; this is the number that proves it doesn't cost the
+hot loop.
+
+### R0 baseline — 2026-07-08 (branch `feat/r0-plugin-module-rails`)
+
+> ⚠️ A quick capture (`--n 50 --soak 8`) against an **empty** library (no charts
+> in `DLC_DIR`), so the `/api/library*` and boot numbers are floor values —
+> re-take on a seeded environment with the recommended `--n 60 --soak 30` for the
+> real R0 baseline before comparing R1+ against it. Recorded here to prove the
+> harness and lock the methodology.
+
+Server latency (ms), n=50:
+
+| Endpoint | status | p50 | p95 | p99 |
+|---|---|---|---|---|
+| `/api/version` | 200 | 0.9 | 1.8 | 22.3 |
+| `/api/plugins` | 200 | 1.6 | 2.1 | 3.4 |
+| `/api/library?limit=60` | 200 | 1.4 | 1.7 | 2.9 |
+| `/api/library/artists` | 200 | 1.3 | 1.8 | 2.7 |
+
+Client:
+
+| Metric | Value |
+|---|---|
+| Cold boot → networkidle | 1268 ms |
+| JS heap after load | 10.1 MB |
+| JS heap after idle soak | 10.1 MB (no idle growth) |
+| Plugin scripts injected | 12 |
+
+No plugin has migrated yet, so all 12 are classic. When the R1 pilot (stems)
+lands, cold-boot / heap should not regress.

docs/plugin-modules.md

@@ -0,0 +1,103 @@
+# Plugin ES-module migration playbook
+
+How to move a plugin off a single global-scope `screen.js` IIFE onto a native
+ES-module graph — **no build step, no framework, no bundler**. This is the
+mechanism the monolith-killing refactor uses; the host rails for it shipped in
+R0 (see `.specify/memory/constitution.md` Principle II + the "Module load
+contract" in Operating Constraints).
+
+## The shape
+
+```
+my-plugin/
+  plugin.json      +  "scriptType": "module"        ← opt in
+  screen.js           import './src/main.js';        ← the entire file
+  src/
+    state.js          (0) module state + accessors
+    util/…            (1) pure helpers — real-import testable
+    …/…               (2..4) model → render/audio/io → input
+    globals.js        (5) THE ONLY file that writes window.*
+    main.js           (5) boot: wire modules, register screen:changed
+  assets/…            worklets / WASM / images (unchanged, served as today)
+```
+
+`screen.js` becomes a one-line static `import`. The host injects it as
+`<script type="module">`, whose load event fires **only after the whole
+static-import graph fetches and evaluates** — so the loader's
+completion-by-`onload` + `_loadingPluginId` window + `playSong` wrapper-chain
+order are all preserved. (A classic IIFE that fired a fire-and-forget
+`import()` would break that contract — don't do that; use `scriptType:"module"`.)
+
+## Non-negotiable rules
+
+1. **Source-served, no build.** Modules are plain source files fetched from
+   `/api/plugins/<id>/src/<path>`. No bundler, transpiler, or TypeScript.
+2. **Layering points downward** — `state → util → commands/model →
+   render/audio/io → input → globals/main`. A lint check (`import-x/no-cycle`)
+   enforces acyclicity; extract bottom-up so each move only imports
+   already-extracted layers.
+3. **`globals.js` is the only writer of `window.*`.** The deliberate global
+   surface shrinks to one auditable file; everything else is module-scoped.
+4. **Import-time purity.** `node --test` runs a module's top-level code on
+   import, so a module you want to unit-test must be side-effect-free at import:
+   no `document` / `window` / `localStorage` at module top level — lift init
+   into an exported `init()` called by `main.js`. (Constitution Principle V's
+   "no implicit IO at import time", applied to the frontend.) Tests are `.mjs`
+   and use real `import`, retiring the regex/`extractFunction` harness.
+5. **Assets resolve via `import.meta.url`.** `document.currentScript` is `null`
+   inside a module. `assets/` lives at the plugin root, so a `src/` module must
+   climb out of `src/`: from `src/main.js`, `new URL('../assets/x.js',
+   import.meta.url)` (deeper modules need more `../`). Simpler and
+   depth-independent: the absolute route `/api/plugins/<id>/assets/x.js`.
+   Worklets run in a *separate* module graph (`AudioWorkletGlobalScope`) and
+   cannot share modules with `src/`.
+6. **Re-init comes from `screen:changed`, not re-execution.** The host loads
+   `screen.js` once per version and `showScreen` re-injects nothing, so module
+   top-level code does **not** re-run when the user re-enters the screen at the
+   same version. Keep per-visit setup/teardown in a `window.feedBack.on(
+   'screen:changed', …)` handler — exactly as classic plugins (tuner,
+   minigames) already do. Do not rely on the IIFE re-running.
+7. **Inline `onclick=` keeps working** during migration via `globals.js` (which
+   keeps every referenced symbol on `window`); retire inline handlers to
+   module-side `addEventListener` opportunistically, never as a blocking step.
+
+## The live-edit loop
+
+The host serves `screen.js`, `src/**`, and `assets/**` with
+`Cache-Control: no-cache` + a weak `ETag` and honors `If-None-Match` → `304`.
+So: edit a `src/` file → **refresh the browser** → the edited module returns
+`200` and reloads while every unchanged module `304`s. There is no hot-reload;
+the loop is edit → refresh → see change, exactly as before. The `?v=<version>`
+query on `screen.js` is the legacy version buster; it does **not** propagate
+into the `src/` graph and does not need to — ETag/mtime is the correctness
+authority for the whole graph.
+
+## Host-version floor (`minHost`)
+
+A migrated plugin *requires* a host new enough to serve `src/` and inject
+`type=module`. Declare the floor with `"minHost": "X.Y.Z"` in `plugin.json`.
+(R0 plumbs the field through `/api/plugins`; enforcement — refuse-with-message
+on an older host — is deferred, so bundled plugins are unaffected. Community
+plugins should state the floor and not migrate below it.)
+
+## Migration mechanics
+
+- **Move-only PRs.** One slice extracts one module: cut code, add
+  imports/exports, update `globals.js` — zero behavior change. Behavior fixes
+  are separate PRs. (Init-lifts for import purity are the one non-pure move —
+  budget them.)
+- **Bottom-up, layer by layer.** Within a layer, independent modules are
+  independent PRs (a DAG, not a chain); use a git worktree per branch.
+- Tests move with their subject and convert to real `.mjs` imports in the same
+  PR (assertions unchanged).
+- Size norm: no source file over **1,500 lines**; legitimate exceptions
+  (hot renderers, etc.) go in the signed register at `docs/size-exemptions.md`.
+
+## Verifying a migration
+
+`node --test <plugin>/tests/*.mjs`; load the plugin on the `:8000` testbed and
+confirm it boots (`<script type=module>` in DevTools, the `src/` graph in
+Network); edit a `src/` file → refresh → change visible (`200` on the edited
+file, `304` on the rest); leave and re-enter the screen at the same version →
+it re-inits via `screen:changed`. The R1 pilots (stems, then studio) certify
+this end-to-end before the flagship repos migrate.

docs/size-exemptions.md

@@ -0,0 +1,66 @@
+# Size-exemption register
+
+The working norm (constitution Principle II; enforced by the `max-lines` lint
+gate) is **no source file over 1,500 lines**. A few files are allowed to exceed
+it because splitting them would do more harm than good — hot per-frame
+renderers, C++, offline generators, cohesive registries. This register is the
+list of those exceptions: each row is a **deliberate, signed** decision with a
+ceiling, a rationale, and a review trigger. Without it, "no file over 1,500
+without a *signed* exemption" is unenforceable.
+
+**Rules**
+- One row per file: a ceiling, a rationale, a signer, a review trigger.
+- The `max-lines` per-file ceilings in `eslint.config.js` mirror this table —
+  keep them in sync (this register is canonical).
+- Files with a scheduled split **plan** are *not* exempt — they live in
+  "Planned, not exempt" at the bottom so nothing falls between the two states.
+- **Signers** (decided 2026-07-08): **Byron** signs core + bundled rows;
+  **Christian** signs the authored-plugin row (virtuoso, its own repo/track).
+
+## Permanent exemptions (structural rationale)
+
+| Repo / file | Lines (7-07) | Ceiling | Rationale | Signer | Review |
+|---|---|---|---|---|---|
+| core `static/highway.js` → residual `renderer-2d.js` (post-split) | ~2,400–2,900 est. | **3,000** | 60 fps hot path; no module boundary inside the per-frame loop | Byron | after the highway.js split |
+| core `plugins/highway_3d/` → residual renderer | sized at split; likely **>3,000** | set at split, flagged now | same hot-path rule; the draw core can't be cut without behavior risk | Byron | after the highway_3d split |
+| core `static/capabilities.js` | 1,538 | 1,600 | cohesive registry + `window.feedBack` bus, 38 lines over; a split spends credibility for nothing | Byron | R4 |
+| tutorials `builtin/reading-the-highway/generate.py` | 1,818 | 2,000 | offline content generator, never imported at runtime, deps not in runtime requirements | Byron | if a 3rd builtin pack appears |
+| desktop `src/audio/NodeAddon.cpp` | 3,542 | as-is | C++, outside the ESM/routes playbooks; under active use-after-free crash work — do not churn | Byron | after crash-class work settles |
+| desktop `src/audio/AudioEngine.cpp` | 2,977 | as-is | same | Byron | same |
+| desktop `src/vst-host/main.cpp` | 1,928 | as-is | same | Byron | same |
+| virtuoso `screen.js` (authored, own track) | 25,741 | as-is until its own split | authored plugin on a separate roadmap; migrates on its own schedule | Christian | virtuoso split kickoff |
+
+## Split-when-touched (no scheduled train; row retires when split)
+
+| Repo / file | Lines | Ceiling | Rationale | Signer | Review |
+|---|---|---|---|---|---|
+| core `lib/gp2rs_gpx.py` | 2,540 | as-is | import converter, off the serve-path hot loop | Byron | when next touched |
+| core `lib/gp2rs.py` | 2,055 | as-is | same | Byron | when next touched |
+| core `lib/song.py` | 1,689 | as-is | data models + wire format; cohesive | Byron | when next touched |
+| core `lib/gp_autosync.py` | 1,572 | as-is | under active dev (#787/#791) — don't collide | Byron | after in-flight work lands |
+| core `plugins/capability_inspector/screen.js` | 1,752 | as-is | bundled diagnostics plugin, low churn | Byron | when next touched |
+| core `plugins/folder_library/screen.js` | 1,672 | as-is | bundled plugin, low churn | Byron | when next touched |
+
+## Temporary rows (cleared by a scheduled PR)
+
+| Repo / file | Lines | Cleared by |
+|---|---|---|
+| core `plugins/__init__.py` | ~2,470 (grew under R0) | the `plugins/_routes.py` + `plugins/_registry.py` split (rides the server.py router work) |
+
+## Watch list (under the norm — no row needed, re-census each phase)
+
+`musicxml-import/mxml2notation.py` (1,456) · core `static/capabilities/audio-effects.js`
+(1,436) · `studio routes.py` (1,399) · `update-manager screen.js` (1,492 — zero headroom).
+
+## Planned, NOT exempt (owned by split plans — listed so nothing falls between states)
+
+core `static/app.js` (11,852) · `static/highway.js` (4,168, whole file) · `server.py`
+(7,880 — was 14,037; ratcheted by the R3 `MetadataDB` + `AudioEffectsMappingDB`
+extractions and seven `routers/` modules) ·
+`lib/metadata_db.py` (4,373 — new in R3; the `MetadataDB` class alone is 4,018 lines
+and is a monolith in its own right, to be split per-table once the router train
+lands) · `static/v3/songs.js` (4,134) · `static/capabilities/audio-session.js`
+(2,974) · `plugins/highway_3d/screen.js` (15,656) · `plugins/keys_highway_3d/screen.js`
+(3,780) · `plugins/drum_highway_3d/screen.js` (3,597) — and every monolith with a PR
+train in the refactor plan. Test files (e.g. `tests/test_plugins.py`) are out of scope
+by policy — the norm governs source files.

eslint.config.js

@@ -0,0 +1,66 @@
+// Flat ESLint config — MAINTAINER / CI ONLY. Never runs on the serve or Docker
+// path (constitution Principle I: dev-only tooling is exempt, same category as
+// scripts/build-tailwind.sh). It enforces the module-migration guardrails:
+//
+//   * max-lines — the 1,500-line size norm, as a WARNING ratchet. Legacy
+//     monoliths warn (the "this is over the norm, split it" signal) and shrink
+//     as the refactor lands; warnings do not fail CI. Genuinely-large files are
+//     exempted below, mirroring the signed register in docs/size-exemptions.md.
+//   * import-x/no-unresolved + no-cycle — module hygiene, scoped to the real
+//     ES-module graphs the refactor produces (a plugin's src/ tree, .mjs
+//     tests). no-unresolved (a HARD error) catches broken import paths;
+//     no-cycle enforces the downward-only layering rule. Core's classic scripts
+//     have no import graph, so both are dormant today and become live gates the
+//     moment module code appears — validated against the first real module
+//     plugin (R1 pilot).
+
+const importX = require('eslint-plugin-import-x');
+
+// Per-file size ceilings — a mirror of docs/size-exemptions.md (canonical).
+// Keep in sync; each entry corresponds to a signed row in the register.
+const SIZE_EXEMPTIONS = [
+    { files: ['**/static/capabilities.js'], max: 1600 },
+    { files: ['**/plugins/capability_inspector/screen.js'], max: 100000 },
+    { files: ['**/plugins/folder_library/screen.js'], max: 100000 },
+];
+
+const sizeRule = (max) => ['warn', { max, skipBlankLines: false, skipComments: false }];
+
+module.exports = [
+    {
+        ignores: [
+            'node_modules/**',
+            'static/vendor/**',
+            'plugins/**/assets/vendor/**',
+            '**/*.min.js',
+            'static/tailwind.min.css',
+        ],
+    },
+    // Size norm across all first-party JS. Classic scripts are parsed as
+    // scripts (no import/export); module files get their own block below.
+    {
+        files: ['**/*.js', '**/*.cjs'],
+        languageOptions: { ecmaVersion: 'latest', sourceType: 'script' },
+        rules: { 'max-lines': sizeRule(1500) },
+    },
+    // ES-module graphs (a plugin's src/ tree, .mjs tests): module parsing + the
+    // acyclic-imports hard gate + the size norm. A migrated bundled plugin's
+    // entry `import './src/main.js'` screen.js must parse as a module — add its
+    // glob here in that plugin's migration PR (classic screen.js stays a script).
+    {
+        files: ['**/src/**/*.js', '**/*.mjs'],
+        languageOptions: { ecmaVersion: 'latest', sourceType: 'module' },
+        plugins: { 'import-x': importX },
+        // v4 flat-config resolver (resolver-next + createNodeResolver). Without
+        // it the import rules silently skip imports they can't resolve.
+        settings: { 'import-x/resolver-next': [importX.createNodeResolver()] },
+        rules: {
+            'max-lines': sizeRule(1500),
+            'import-x/no-unresolved': 'error',
+            'import-x/no-cycle': 'error',
+        },
+    },
+    // Signed size exemptions (docs/size-exemptions.md) — raise the ceiling so
+    // registered files don't warn below it.
+    ...SIZE_EXEMPTIONS.map(({ files, max }) => ({ files, rules: { 'max-lines': sizeRule(max) } })),
+];

lib/appstate.py

@@ -0,0 +1,102 @@
+"""Shared application state — the seam that lets route modules reach core
+singletons without importing ``server``.
+
+``server.py`` is the host: it owns the FastAPI ``app``, constructs the DB
+singletons, and runs the lifecycle. As routes move out into ``routers/`` (R3),
+those modules need ``meta_db`` and friends — but they must not ``import
+server``, or the import graph goes circular the moment ``server`` imports them
+back.
+
+So ``server`` **injects** its singletons here once, at the point it builds them::
+
+    # server.py
+    meta_db = MetadataDB(CONFIG_DIR)
+    appstate.configure(meta_db=meta_db, ...)
+
+and a router reads them back as **module attributes, at call time**::
+
+    # routers/artists.py
+    import appstate
+
+    @router.get("/api/artist/{name}/page")
+    def artist_page(name):
+        return appstate.meta_db.artist_page(name)
+
+This is the Python analogue of the injected `configureX({...})` seams the
+frontend refactor uses (stems' ``configureStreaming``, studio's
+``configureAudioGraph``, the editor's ``src/host.js``), and of the plugin
+``setup(app, context)`` contract in Principle III: dependencies flow one way,
+``server -> routers -> appstate``, and nothing imports back up.
+
+Two properties this shape buys, both load-bearing:
+
+* **``import appstate`` performs no IO and constructs nothing.** ``server``
+  still owns construction, so the ~49 test fixtures that do
+  ``sys.modules.pop("server")`` + re-import (to rebuild ``meta_db`` under a
+  patched ``CONFIG_DIR``) keep working untouched — a singleton *owned* here
+  would survive that pop and go stale.
+* **Reads are late-bound.** Routers must use ``appstate.meta_db``, never
+  ``from appstate import meta_db`` — a ``from`` import freezes the binding at
+  its current value, so a later ``configure()`` (or a
+  ``monkeypatch.setattr(appstate, "meta_db", fake)``) would not reach the
+  router. This is the same read-only-binding trap as ES ``import``.
+
+Defaults are ``None`` on purpose: they are inert but *type-honest*, so a router
+that runs before ``configure()`` fails loudly on ``NoneType`` instead of
+quietly operating on a stand-in.
+
+Slots are added here only when a router actually needs one — this is a seam,
+not a grab-bag for everything in ``server.py``.
+
+**Why this lives in ``lib/`` and not the repo root.** Because it constructs
+nothing and does no import-time IO, it satisfies Principle V's rule for ``lib/``
+modules — and ``lib/`` is the only core directory every packaging path already
+copies: the Dockerfile (``COPY lib/``), ``docker-compose.yml``, and
+feedback-desktop's ``bundle-slopsmith.sh`` (``cp -r lib``). All three also put
+both the bundle root and ``lib/`` on ``sys.path``. A root-level module ships in
+Docker but is silently dropped from the packaged desktop app, whose bundler
+copies a hardcoded file list — that regression is what moved this file here.
+"""
+
+# The singletons routers may read. Every name here must also be a `_SLOTS` key.
+meta_db = None
+audio_effect_mappings = None
+
+# Config paths. server.py derives these from the environment (fresh on every
+# import, so the ~49 pop-and-reimport fixtures keep working) and injects them
+# here. Routers read them as `appstate.config_dir` etc. — a module attribute at
+# call time. NOTE: config_dir/dlc_dir are env-derived, so a `setenv`+reimport
+# test reconfigures them for free; STATIC_DIR/SLOPPAK_CACHE_DIR are patched via
+# `setattr(server, …)` in a few tests, so those slots (when added) need their
+# tests retargeted to appstate in the same PR.
+config_dir = None
+dlc_dir = None          # the DLC_DIR env value as a Path (Path("") if unset)
+dlc_dir_env = None      # the raw DLC_DIR env string, "" if unset — distinguishes
+                        # "unset" from Path("")→"." (see dlc_paths._get_dlc_dir)
+# Cache/asset dirs. static_dir + sloppak_cache_dir are patched via
+# `setattr(server, …)` in a few tests, so a router reading them here needs those
+# setattr sites retargeted to `setattr(appstate, …)` in the same PR (ws_highway
+# retargets the 3 test_highway_ws_* SLOPPAK sites). config_dir-derived dirs are
+# reconfigured for free on a setenv+reimport.
+static_dir = None
+sloppak_cache_dir = None
+audio_cache_dir = None
+
+_SLOTS = frozenset({
+    "meta_db", "audio_effect_mappings",
+    "config_dir", "dlc_dir", "dlc_dir_env",
+    "static_dir", "sloppak_cache_dir", "audio_cache_dir",
+})
+
+
+def configure(**kwargs) -> None:
+    """Publish `server`'s singletons into this module. Called once per
+    `server` import (and again on re-import), so it must be idempotent."""
+    unknown = set(kwargs) - _SLOTS
+    if unknown:
+        raise TypeError(
+            f"appstate.configure() got unknown slot(s): {sorted(unknown)}. "
+            f"Known slots: {sorted(_SLOTS)}. Add the name to _SLOTS if a router "
+            f"genuinely needs it."
+        )
+    globals().update(kwargs)

lib/audio_effects_db.py

@@ -0,0 +1,287 @@
+"""Core-owned song/tone -> audio-effect-provider mapping index.
+
+Extracted verbatim from ``server.py`` (R3). ``server.py`` still owns the
+``audio_effect_mappings`` singleton; this module only supplies the class, so
+nothing here touches config paths at import time — the caller passes
+``config_dir`` in.
+"""
+
+import json
+import sqlite3
+import threading
+from pathlib import Path
+
+
+class AudioEffectsMappingDB:
+    """Core-owned public song/tone -> provider mapping index.
+
+    Providers own the preset/chain rows addressed by provider_ref. Core owns
+    the cross-provider routing index and the active mapping per song/tone.
+    """
+
+    def __init__(self, config_dir: Path):
+        config_dir.mkdir(parents=True, exist_ok=True)
+        self.db_path = str(config_dir / "audio_effects.db")
+        self.conn = sqlite3.connect(self.db_path, check_same_thread=False)
+        self.conn.execute("PRAGMA journal_mode=WAL")
+        self.conn.execute("PRAGMA foreign_keys=ON")
+        self.conn.execute("""
+            CREATE TABLE IF NOT EXISTS audio_effect_mappings (
+                id INTEGER PRIMARY KEY AUTOINCREMENT,
+                song_key TEXT NOT NULL,
+                filename TEXT NOT NULL DEFAULT '',
+                tone_key TEXT NOT NULL,
+                provider_id TEXT NOT NULL,
+                provider_ref TEXT NOT NULL,
+                label TEXT NOT NULL DEFAULT '',
+                source TEXT NOT NULL DEFAULT 'manual',
+                metadata_json TEXT NOT NULL DEFAULT '{}',
+                created_at TEXT NOT NULL DEFAULT (datetime('now')),
+                updated_at TEXT NOT NULL DEFAULT (datetime('now')),
+                UNIQUE(song_key, tone_key, provider_id)
+            )
+        """)
+        self.conn.execute("""
+            CREATE TABLE IF NOT EXISTS audio_effect_active_mappings (
+                song_key TEXT NOT NULL,
+                tone_key TEXT NOT NULL,
+                mapping_id INTEGER NOT NULL,
+                updated_at TEXT NOT NULL DEFAULT (datetime('now')),
+                PRIMARY KEY (song_key, tone_key),
+                FOREIGN KEY (mapping_id) REFERENCES audio_effect_mappings(id) ON DELETE CASCADE
+            )
+        """)
+        self.conn.execute(
+            "CREATE INDEX IF NOT EXISTS idx_audio_effect_mappings_provider "
+            "ON audio_effect_mappings(provider_id)"
+        )
+        self.conn.execute(
+            "CREATE INDEX IF NOT EXISTS idx_audio_effect_mappings_filename "
+            "ON audio_effect_mappings(filename)"
+        )
+        self.conn.commit()
+        self._lock = threading.Lock()
+
+    @staticmethod
+    def _text(value, *, field: str, limit: int, allow_empty: bool = False) -> str:
+        if value is None:
+            text = ""
+        elif not isinstance(value, str):
+            raise ValueError(f"{field} must be a string")
+        else:
+            text = value.strip()
+        if not text and not allow_empty:
+            raise ValueError(f"{field} is required")
+        if len(text) > limit:
+            raise ValueError(f"{field} is too long")
+        return text
+
+    @staticmethod
+    def _mapping_id(value) -> int | None:
+        # Bind only values SQLite can store as an INTEGER; an out-of-range id is a
+        # clean miss (404), not a 500 at bind time.
+        if isinstance(value, int) and not isinstance(value, bool) and -(2 ** 63) <= value < 2 ** 63:
+            return value
+        return None
+
+    @staticmethod
+    def _field(data: dict, *keys):
+        # Select the first present snake/camel alias by key, not by truthiness, so a
+        # falsey non-string value (false/0) still reaches _text() and is rejected
+        # instead of being silently swallowed by an `or` chain.
+        for key in keys:
+            if key in data:
+                return data[key]
+        return None
+
+    @staticmethod
+    def _metadata(value) -> str:
+        if value is None:
+            return "{}"
+        if not isinstance(value, dict):
+            raise ValueError("metadata must be an object")
+        encoded = json.dumps(value, ensure_ascii=True, sort_keys=True)
+        if len(encoded) > 8192:
+            raise ValueError("metadata is too large")
+        return encoded
+
+    @staticmethod
+    def _row(row) -> dict | None:
+        if row is None:
+            return None
+        metadata = {}
+        try:
+            metadata = json.loads(row[8]) if row[8] else {}
+        except Exception:
+            metadata = {}
+        return {
+            "id": int(row[0]),
+            "song_key": row[1],
+            "filename": row[2] or "",
+            "tone_key": row[3],
+            "provider_id": row[4],
+            "provider_ref": row[5],
+            "label": row[6] or "",
+            "source": row[7] or "manual",
+            "metadata": metadata if isinstance(metadata, dict) else {},
+            "created_at": row[9] or "",
+            "updated_at": row[10] or "",
+            "active": bool(row[11]),
+        }
+
+    def _select_sql(self) -> str:
+        return """
+            SELECT m.id, m.song_key, m.filename, m.tone_key, m.provider_id,
+                   m.provider_ref, m.label, m.source, m.metadata_json,
+                   m.created_at, m.updated_at,
+                   CASE WHEN a.mapping_id IS NULL THEN 0 ELSE 1 END AS active
+            FROM audio_effect_mappings m
+            LEFT JOIN audio_effect_active_mappings a
+              ON a.song_key = m.song_key AND a.tone_key = m.tone_key AND a.mapping_id = m.id
+        """
+
+    def list(self, *, song_key: str = "", filename: str = "", tone_key: str = "", provider_id: str = "") -> list[dict]:
+        clauses: list[str] = []
+        params: list[str] = []
+        song_key = self._text(song_key, field="song_key", limit=240, allow_empty=True)
+        filename = self._text(filename, field="filename", limit=500, allow_empty=True)
+        tone_key = self._text(tone_key, field="tone_key", limit=160, allow_empty=True)
+        provider_id = self._text(provider_id, field="provider_id", limit=96, allow_empty=True)
+        if song_key and filename:
+            clauses.append("(m.song_key = ? OR m.filename = ?)")
+            params.extend([song_key, filename])
+        elif song_key:
+            clauses.append("m.song_key = ?")
+            params.append(song_key)
+        elif filename:
+            clauses.append("(m.song_key = ? OR m.filename = ?)")
+            params.extend([filename, filename])
+        if tone_key:
+            clauses.append("m.tone_key = ?")
+            params.append(tone_key)
+        if provider_id:
+            clauses.append("m.provider_id = ?")
+            params.append(provider_id)
+        sql = self._select_sql()
+        if clauses:
+            sql += " WHERE " + " AND ".join(clauses)
+        sql += " ORDER BY m.song_key COLLATE NOCASE, m.tone_key COLLATE NOCASE, m.provider_id COLLATE NOCASE"
+        with self._lock:
+            rows = self.conn.execute(sql, params).fetchall()
+        return [self._row(row) for row in rows]
+
+    def get(self, mapping_id: int) -> dict | None:
+        mapping_id = self._mapping_id(mapping_id)
+        if mapping_id is None:
+            return None
+        with self._lock:
+            row = self.conn.execute(self._select_sql() + " WHERE m.id = ?", (mapping_id,)).fetchone()
+        return self._row(row)
+
+    def upsert(self, data: dict) -> dict:
+        if not isinstance(data, dict):
+            raise ValueError("mapping body must be an object")
+        filename = self._text(data.get("filename", ""), field="filename", limit=500, allow_empty=True)
+        song_key_raw = self._field(data, "song_key", "songKey")
+        if song_key_raw is None or song_key_raw == "":
+            song_key_raw = filename
+        song_key = self._text(song_key_raw, field="song_key", limit=240)
+        tone_key = self._text(self._field(data, "tone_key", "toneKey"), field="tone_key", limit=160, allow_empty=True)
+        provider_id = self._text(self._field(data, "provider_id", "providerId"), field="provider_id", limit=96)
+        provider_ref = self._text(self._field(data, "provider_ref", "providerRef"), field="provider_ref", limit=240)
+        label = self._text(data.get("label", ""), field="label", limit=160, allow_empty=True)
+        source = self._text(data.get("source", "manual"), field="source", limit=40, allow_empty=True) or "manual"
+        metadata_json = self._metadata(data.get("metadata", {}))
+        with self._lock:
+            self.conn.execute(
+                """
+                INSERT INTO audio_effect_mappings
+                    (song_key, filename, tone_key, provider_id, provider_ref, label, source, metadata_json, updated_at)
+                VALUES (?, ?, ?, ?, ?, ?, ?, ?, datetime('now'))
+                ON CONFLICT(song_key, tone_key, provider_id) DO UPDATE SET
+                    -- Only overwrite filename when a non-empty one was supplied; an
+                    -- omitted/empty filename must preserve the stored value (it's an
+                    -- alternate lookup key for list(..., filename=...)).
+                    filename=CASE WHEN excluded.filename <> '' THEN excluded.filename ELSE audio_effect_mappings.filename END,
+                    provider_ref=excluded.provider_ref,
+                    label=excluded.label,
+                    source=excluded.source,
+                    metadata_json=excluded.metadata_json,
+                    updated_at=datetime('now')
+                """,
+                (song_key, filename, tone_key, provider_id, provider_ref, label, source, metadata_json),
+            )
+            row = self.conn.execute(
+                "SELECT id FROM audio_effect_mappings WHERE song_key = ? AND tone_key = ? AND provider_id = ?",
+                (song_key, tone_key, provider_id),
+            ).fetchone()
+            if row is None:
+                raise ValueError("failed to create audio-effects mapping")
+            mapping_id = int(row[0])
+            if data.get("active") is True:
+                self.conn.execute(
+                    """
+                    INSERT INTO audio_effect_active_mappings (song_key, tone_key, mapping_id, updated_at)
+                    VALUES (?, ?, ?, datetime('now'))
+                    ON CONFLICT(song_key, tone_key) DO UPDATE SET
+                        mapping_id=excluded.mapping_id,
+                        updated_at=datetime('now')
+                    """,
+                    (song_key, tone_key, mapping_id),
+                )
+            self.conn.commit()
+        return self.get(mapping_id)
+
+    def delete(self, mapping_id: int, *, provider_id: str = "") -> bool:
+        mapping_id = self._mapping_id(mapping_id)
+        if mapping_id is None:
+            return False
+        provider_id = self._text(provider_id, field="provider_id", limit=96, allow_empty=True)
+        with self._lock:
+            if provider_id:
+                cur = self.conn.execute(
+                    "DELETE FROM audio_effect_mappings WHERE id = ? AND provider_id = ?",
+                    (mapping_id, provider_id),
+                )
+            else:
+                cur = self.conn.execute("DELETE FROM audio_effect_mappings WHERE id = ?", (mapping_id,))
+            self.conn.commit()
+            return cur.rowcount > 0
+
+    def activate(self, mapping_id: int, *, provider_id: str = "") -> dict | None:
+        mapping_id = self._mapping_id(mapping_id)
+        if mapping_id is None:
+            return None
+        provider_id = self._text(provider_id, field="provider_id", limit=96, allow_empty=True)
+        with self._lock:
+            row = self.conn.execute(
+                self._select_sql() + " WHERE m.id = ?",
+                (mapping_id,),
+            ).fetchone()
+            mapping = self._row(row)
+            if not mapping or (provider_id and mapping["provider_id"] != provider_id):
+                return None
+            self.conn.execute(
+                """
+                INSERT INTO audio_effect_active_mappings (song_key, tone_key, mapping_id, updated_at)
+                VALUES (?, ?, ?, datetime('now'))
+                ON CONFLICT(song_key, tone_key) DO UPDATE SET
+                    mapping_id=excluded.mapping_id,
+                    updated_at=datetime('now')
+                """,
+                (mapping["song_key"], mapping["tone_key"], mapping_id),
+            )
+            self.conn.commit()
+            selected = self.conn.execute(self._select_sql() + " WHERE m.id = ?", (mapping_id,)).fetchone()
+        return self._row(selected)
+
+    def clear_active(self, *, song_key: str, tone_key: str) -> bool:
+        song_key = self._text(song_key, field="song_key", limit=240)
+        tone_key = self._text(tone_key, field="tone_key", limit=160, allow_empty=True)
+        with self._lock:
+            cur = self.conn.execute(
+                "DELETE FROM audio_effect_active_mappings WHERE song_key = ? AND tone_key = ?",
+                (song_key, tone_key),
+            )
+            self.conn.commit()
+            return cur.rowcount > 0

lib/dlc_paths.py

@@ -0,0 +1,99 @@
+"""DLC library path resolution — where the song files live, plus safe containment.
+
+Extracted from ``server.py`` (R3). ``_resolve_dlc_path`` is pure and moved
+verbatim. ``_get_dlc_dir`` reads the env-derived paths through the ``appstate``
+seam (``server.py`` configures ``dlc_dir``/``dlc_dir_env``/``config_dir`` at
+import, fresh on every re-import), so this module does no import-time IO and the
+pop-and-reimport fixtures keep working. ``server.py`` re-exports both names, so
+existing ``server._get_dlc_dir`` / ``server._resolve_dlc_path`` references
+(tests, other handlers) resolve unchanged.
+"""
+
+import json
+import os
+from pathlib import Path
+
+import appstate
+
+
+def _get_dlc_dir(cfg: dict | None = None) -> Path | None:
+    # Only consider DLC_DIR if the env var was non-empty. `Path("")` collapses
+    # to `.` and reports `.is_dir() == True`, which would silently shadow the
+    # config.json fallback. Checking the raw env string preserves
+    # `DLC_DIR=.` as a valid opt-in for cwd while keeping unset/empty out.
+    if appstate.dlc_dir_env and appstate.dlc_dir.is_dir():
+        return appstate.dlc_dir
+    if cfg is None:
+        config_file = appstate.config_dir / "config.json"
+        if config_file.exists():
+            try:
+                cfg = json.loads(config_file.read_text(encoding="utf-8"))
+            except Exception:
+                pass
+    if isinstance(cfg, dict):
+        raw = str(cfg.get("dlc_dir", "")).strip()
+        if raw:
+            p = Path(raw)
+            if p.is_dir():
+                return p
+    return None
+
+
+def _resolve_dlc_path(dlc: Path, filename: str) -> Path | None:
+    """Resolve `filename` under DLC_DIR and refuse anything that escapes.
+
+    `filename` arrives from `:path` route params and can contain `..`
+    segments. The Sloppak and archive paths happen to fail safely later
+    because their loaders raise on missing/invalid files, but loose-
+    folder format detection (`is_loose_song`) globs and parses XML on
+    disk first, which lets a crafted path trigger filesystem reads
+    outside DLC_DIR before any guard fires. Centralise the containment
+    check so every filename-bound handler validates before touching the
+    filesystem.
+
+    Containment here is LEXICAL (normalize `.`/`..` WITHOUT following
+    symlinks), not `safe_join`'s `.resolve()`-based check — because users
+    commonly mount their song library through a directory JUNCTION/symlink
+    (a library shared across app installs; the desktop app's own mounts).
+    `.resolve()` follows that junction to its real target, sees it sits
+    outside DLC_DIR, and wrongly rejects every song reached through it — the
+    scanner's `rglob` indexes those songs, but art/load then 403/404s (broken
+    covers, unplayable songs). Lexical normalization still rejects the only
+    escapes a `:path` filename can express — `..` traversal and absolute
+    paths — which the traversal tests pin. `safe_join` stays strict (it is
+    the zip-slip / plugin-asset guard, where following a symlink out IS the
+    defense); the loose-folder art handler keeps its own per-file symlink
+    re-check for defence-in-depth.
+
+    Returns the validated Path (not necessarily link-resolved), or None if
+    the filename is empty, contains a NUL, or escapes the DLC root.
+    """
+    if not filename:
+        return None
+    # Backslashes → forward slashes so a Windows-style `..\\x` traversal is
+    # rejected identically on POSIX (mirrors safe_join's normalisation).
+    safe = filename.replace("\\", "/")
+    if "\x00" in safe:
+        return None
+    # Reject drive-letter / absolute paths in BOTH conventions. A POSIX "/x" is
+    # caught by the containment check below (the `/` operator discards `root`),
+    # but a Windows drive-absolute "C:/x" is treated as a relative "C:" dir on
+    # POSIX and would otherwise slip in as `<root>/C:/x` — so the contract must
+    # hold cross-platform (a shared library is reached from either OS).
+    from pathlib import PurePosixPath, PureWindowsPath
+    if (PurePosixPath(safe).is_absolute()
+            or PureWindowsPath(safe).is_absolute()
+            or PureWindowsPath(safe).drive):
+        return None
+    try:
+        root = dlc.resolve()
+        # normpath collapses `.`/`..`/duplicate separators purely lexically —
+        # it never touches the filesystem, so an in-library junction component
+        # is preserved (allowed) while `..`/absolute segments still escape and
+        # get caught by the containment check below.
+        candidate = Path(os.path.normpath(root / safe))
+        if not candidate.is_relative_to(root):
+            return None
+    except (ValueError, OSError):
+        return None
+    return candidate

lib/gp2rs.py

@@ -1114,7 +1114,7 @@ def _build_xml(
     ET.SubElement(root, "arrangement").text = arrangement
     ET.SubElement(root, "offset").text = f"{audio_offset:.3f}"
     ET.SubElement(root, "songLength").text = f"{song_length:.3f}"
-    ET.SubElement(root, "startBeat").text = f"{beats[0].time:.3f}" if beats else "0.000"
+    ET.SubElement(root, "startBeat").text = f"{beats[0].time:.6f}" if beats else "0.000000"
     ET.SubElement(root, "averageTempo").text = str(tempo)
     ET.SubElement(root, "artistName").text = artist
     ET.SubElement(root, "albumName").text = album
@@ -1139,10 +1139,17 @@ def _build_xml(
         tuning_el.set(f"string{i}", str(tuning[i] if i < len(tuning) else 0))
     ET.SubElement(root, "capo").text = "0"
 
-    # Ebeats
+    # Ebeats — write beat times at MICROSECOND (6-decimal) precision, not
+    # millisecond (3-decimal). The editor/timeline DERIVES per-bar BPM from beat
+    # spans (bpm = beats·60/span), which amplifies any rounding: at 3 decimals a
+    # constant-tempo GP (e.g. 140) shows a spurious ±0.05–0.7 BPM per-bar drift
+    # (worse for fast/odd meters) because most bar lengths don't land on a ms
+    # boundary. gp2rs computes these times exactly from the GP tempo map, so the
+    # only loss is this format string — 6 decimals makes the derived tempo match
+    # GP's authored value. (Everything else stays at :.3f; only beats drive tempo.)
     ebeats = ET.SubElement(root, "ebeats", count=str(len(beats)))
     for b in beats:
-        ET.SubElement(ebeats, "ebeat", time=f"{b.time:.3f}", measure=str(b.measure))
+        ET.SubElement(ebeats, "ebeat", time=f"{b.time:.6f}", measure=str(b.measure))
 
     # Sections
     sections_el = ET.SubElement(root, "sections", count=str(len(sections)))
@@ -1836,9 +1843,10 @@ def convert_drum_track_to_drumtab(
     drum strings. Unknown percussion sounds (cowbell, tambourine etc.) are
     skipped — round-tripping them would require teaching `lib/drums.py` first.
     Callers can pass an empty dict as ``out_unmapped`` to receive a per-MIDI
-    record of every skipped note (``{midi: {"count": int, "times": [...]}}``,
-    times capped at 100 samples per note) so they can surface a warning or
-    offer a manual mapping UI.
+    record of every skipped note (``{midi: {"count": int, "times": [...],
+    "velocities": [...]}}``, times/velocities index-aligned and capped at
+    100 samples per note — velocities carry the source notes' real dynamics)
+    so they can surface a warning or offer a manual mapping UI.
 
     Honours GP repeat brackets and D.S./D.C./Coda/Fine jumps when
     ``expand_repeats`` is true — same `_build_playback_schedule` machinery
@@ -1894,18 +1902,29 @@ def convert_drum_track_to_drumtab(
                             # NB: do NOT shadow the outer `entry` loop
                             # variable from `for entry in schedule:`.
                             unmapped_rec = out_unmapped.setdefault(
-                                int(midi_note), {"count": 0, "times": []})
+                                int(midi_note),
+                                {"count": 0, "times": [], "velocities": []})
                             unmapped_rec["count"] += 1
                             if len(unmapped_rec["times"]) < 100:
                                 unmapped_rec["times"].append(round(t, 3))
+                                # Index-aligned with times: the note's real
+                                # dynamics (same 1-127 gate as mapped hits,
+                                # falling back to the 100 import default) so
+                                # a hand-mapping UI doesn't flatten them.
+                                _uv = int(getattr(note, "velocity", 0) or 0)
+                                unmapped_rec["velocities"].append(
+                                    _uv if 1 <= _uv <= 127 else 100)
                         continue
 
                     hit: dict = {"t": round(t, 3), "p": piece}
 
-                    # Velocity: GP stores 1-127 MIDI velocity directly; default
-                    # is 95 (Velocities.default). Pass through verbatim,
-                    # clamping defensively so a corrupt file can't poison the
-                    # wire format.
+                    # Velocity: GP stores 1-127 MIDI velocity directly. Note
+                    # this is GP's *authoring* default (95, Velocities.default)
+                    # — unrelated to the drumtab render default of 100
+                    # (DEFAULT_VELOCITY, lib/drums.py:179), which only applies
+                    # when `v` is omitted from a hit. Pass the GP value through
+                    # verbatim, clamping defensively so a corrupt file can't
+                    # poison the wire format.
                     vel = int(getattr(note, "velocity", 0) or 0)
                     if 1 <= vel <= 127:
                         hit["v"] = vel
@@ -1946,9 +1965,21 @@ def convert_drum_track_to_drumtab(
     # Times for unmapped notes were collected in beat-iteration order;
     # multi-voice measures can produce out-of-order beats, so sort each
     # entry's `times` list chronologically before returning to the caller.
+    # Velocities are index-aligned with times, so they must sort in
+    # LOCKSTEP — sorting times alone would silently reassign dynamics.
     if out_unmapped is not None:
         for _rec in out_unmapped.values():
-            _rec["times"].sort()
+            _vels = _rec.get("velocities")
+            if _vels and len(_vels) == len(_rec["times"]):
+                _pairs = sorted(zip(_rec["times"], _vels))
+                _rec["times"] = [p[0] for p in _pairs]
+                _rec["velocities"] = [p[1] for p in _pairs]
+            else:
+                # Belt-and-suspenders: times & velocities are always appended
+                # together under the same `len(times) < 100` guard above, so
+                # in practice the lengths can't diverge. Kept as a defensive
+                # fallback, not a real divergence case.
+                _rec["times"].sort()
 
     return {
         "version": drums_mod.SCHEMA_VERSION,

lib/midi_import.py

@@ -634,10 +634,12 @@ def convert_drum_track_from_midi(
 
     Callers can pass an empty dict as ``out_unmapped`` to receive a
     per-MIDI record of every channel-9 note_on that didn't resolve to a
-    piece-id (``{midi: {"count": int, "times": [float, ...]}}``, times
-    capped at 100 samples per note). The default path skips this
-    capture entirely so MIDIs heavy with cowbell/tambourine/etc. take
-    no extra work.
+    piece-id (``{midi: {"count": int, "times": [float, ...],
+    "velocities": [int, ...]}}``, times/velocities index-aligned and
+    capped at 100 samples per note — velocities carry the source notes'
+    real dynamics so a hand-mapping UI doesn't have to flatten them to a
+    default). The default path skips this capture entirely so MIDIs
+    heavy with cowbell/tambourine/etc. take no extra work.
     """
     offset = float(audio_offset)
     if not math.isfinite(offset):
@@ -675,10 +677,13 @@ def convert_drum_track_from_midi(
                     continue
                 t = tick_to_seconds(abs_tick) + offset
                 entry = out_unmapped.setdefault(
-                    midi_note, {"count": 0, "times": []})
+                    midi_note, {"count": 0, "times": [], "velocities": []})
                 entry["count"] += 1
                 if len(entry["times"]) < 100:
                     entry["times"].append(round(t, 3))
+                    # Index-aligned with times: the note's real dynamics,
+                    # so hand-mapping doesn't flatten everything to 100.
+                    entry["velocities"].append(int(msg.velocity))
                 continue
             # Mapped note: compute t once for the raw entry.
             t = tick_to_seconds(abs_tick) + offset

lib/reqfields.py

@@ -0,0 +1,13 @@
+"""Request-field coercion helpers shared by the raw-`dict` POST handlers.
+
+Extracted verbatim from ``server.py`` (R3). Pure — no IO, no globals — so it
+imports cleanly from both ``server`` and any ``routers/`` module.
+"""
+
+
+def _clean_str(value) -> str:
+    """Trim a request field to a string; non-strings (or missing) → ''.
+    Lets the raw-`dict` POST handlers treat wrong-typed JSON (an int/list/etc.
+    where a string was expected) as "empty" and answer 400, instead of raising
+    AttributeError/TypeError → 500 on a later .strip()/`in`."""
+    return value.strip() if isinstance(value, str) else ""

lib/routers/__init__.py

@@ -0,0 +1,31 @@
+"""FastAPI route modules extracted from ``server.py`` (R3).
+
+Each module here exposes a module-level ``router`` (a ``fastapi.APIRouter``)
+that ``server.py`` mounts with ``app.include_router(...)`` at the point in the
+file where those routes used to be defined — FastAPI matches routes in
+registration order, so keeping the mount site preserves it.
+
+**Routers must never ``import server``.** They reach core singletons through
+the injected seam instead::
+
+    import appstate
+
+    @router.get("/api/thing")
+    def get_thing():
+        return appstate.meta_db.thing()
+
+and always as a **module attribute, at call time** — never
+``from appstate import meta_db``, which freezes the binding and defeats both a
+later ``appstate.configure()`` and ``monkeypatch.setattr``. See ``appstate.py``.
+
+Dependencies flow one way: ``server -> routers -> appstate``.
+
+**Why this lives under ``lib/``.** ``lib/`` is the only core directory every
+packaging path already copies wholesale — the Dockerfile (``COPY lib/``),
+``docker-compose.yml``, and feedback-desktop's ``bundle-slopsmith.sh``
+(``cp -r lib``) — and all three put it on ``sys.path``. A root-level package
+ships in Docker but is silently dropped from the packaged desktop app, whose
+bundler copies a hardcoded file list. Route modules import nothing at module
+scope beyond FastAPI and ``appstate``, so they do no import-time IO and satisfy
+Principle V's rule for ``lib/``.
+"""

lib/routers/artist_aliases.py

@@ -0,0 +1,68 @@
+"""Artist aliases / Tidy-up (P4) — canonicalize messy artist tags at DISPLAY
+("ACDC" -> "AC/DC") without touching feedpak files or the scanner-derived
+songs.artist. All DB-only.
+
+Extracted verbatim from ``server.py`` (R3); only the decorator receiver
+(``@app`` -> ``@router``) and the singleton read (``meta_db`` ->
+``appstate.meta_db``) changed. The read stays a module attribute so a re-imported
+``server`` re-publishes a fresh DB into the seam — see ``appstate.py``.
+"""
+
+from fastapi import APIRouter
+from fastapi.responses import JSONResponse
+
+import appstate
+
+router = APIRouter()
+
+
+@router.get("/api/artist-aliases")
+def list_artist_aliases():
+    """Existing raw→canonical overrides (the Tidy-up 'current merges' list)."""
+    return {"aliases": appstate.meta_db.list_artist_aliases()}
+
+
+@router.get("/api/artists/raw")
+def list_raw_artists(limit: int = 2000):
+    """Distinct RAW artist names + song counts + current canonical — the Tidy-up
+    picker (you merge raw variants into one canonical)."""
+    return {"artists": appstate.meta_db.raw_artists(limit)}
+
+
+@router.post("/api/artist-aliases")
+def set_artist_alias(data: dict):
+    """Upsert one override: {raw_name, canonical_name, mb_artist_id?}. A self-alias
+    (raw == canonical) clears the row instead (un-merge)."""
+    raw = (data.get("raw_name") or "").strip()
+    canon = (data.get("canonical_name") or "").strip()
+    if not raw or not canon:
+        return JSONResponse({"error": "raw_name and canonical_name are required"}, 400)
+    result = appstate.meta_db.set_artist_alias(raw, canon, (data.get("mb_artist_id") or None))
+    if not result.get("ok"):
+        # Would form a cycle (raw → … → raw) — refuse rather than corrupt the chain.
+        return JSONResponse(
+            {"error": "alias would create a cycle", "raw_name": raw, "canonical_name": canon},
+            409)
+    return {"ok": True, "raw_name": raw, "canonical_name": result.get("canonical_name", canon)}
+
+
+@router.post("/api/artist-aliases/merge")
+def merge_artist_aliases(data: dict):
+    """Merge several raw artist variants into one canonical:
+    {raw_names: [...], canonical_name}. The canonical's own self-alias is skipped.
+    Returns {merged: N}."""
+    canon = (data.get("canonical_name") or "").strip()
+    raws = data.get("raw_names")
+    if not canon:
+        return JSONResponse({"error": "canonical_name is required"}, 400)
+    if not isinstance(raws, list) or not raws:
+        return JSONResponse({"error": "raw_names must be a non-empty array"}, 400)
+    n = appstate.meta_db.merge_artists(raws, canon)
+    return {"merged": n, "canonical_name": canon}
+
+
+@router.delete("/api/artist-aliases/{raw_name:path}")
+def delete_artist_alias(raw_name: str):
+    """Remove one override so that raw artist stands on its own again."""
+    appstate.meta_db.remove_artist_alias(raw_name)
+    return {"ok": True}

lib/routers/audio_effects.py

@@ -0,0 +1,80 @@
+"""Audio-effects mapping API — the core-owned song/tone -> provider routing index.
+
+Extracted verbatim from ``server.py`` (R3); only the decorator receiver
+(``@app`` -> ``@router``) and the singleton read (``audio_effect_mappings`` ->
+``appstate.audio_effect_mappings``) changed. The read must stay a module
+attribute so a re-imported ``server`` re-publishes a fresh DB into the seam and
+`monkeypatch.setattr` reaches this module — see ``appstate.py``.
+"""
+
+from fastapi import APIRouter, Body, Query
+from fastapi.responses import JSONResponse
+
+import appstate
+
+router = APIRouter()
+
+
+def _audio_effects_error(exc: Exception):
+    return JSONResponse({"error": str(exc)}, status_code=400)
+
+
+@router.get("/api/audio-effects/mappings")
+def list_audio_effect_mappings(
+    song_key: str = Query(""),
+    filename: str = Query(""),
+    tone_key: str = Query(""),
+    provider_id: str = Query(""),
+):
+    try:
+        return {
+            "mappings": appstate.audio_effect_mappings.list(
+                song_key=song_key,
+                filename=filename,
+                tone_key=tone_key,
+                provider_id=provider_id,
+            )
+        }
+    except ValueError as exc:
+        return _audio_effects_error(exc)
+
+
+@router.post("/api/audio-effects/mappings")
+def upsert_audio_effect_mapping(data: dict = Body(...)):
+    try:
+        mapping = appstate.audio_effect_mappings.upsert(data)
+    except ValueError as exc:
+        return _audio_effects_error(exc)
+    return {"ok": True, "mapping": mapping}
+
+
+@router.delete("/api/audio-effects/mappings/{mapping_id}")
+def delete_audio_effect_mapping(mapping_id: int, provider_id: str = Query("")):
+    try:
+        deleted = appstate.audio_effect_mappings.delete(mapping_id, provider_id=provider_id)
+    except ValueError as exc:
+        return _audio_effects_error(exc)
+    if not deleted:
+        return JSONResponse({"error": "mapping not found"}, status_code=404)
+    return {"ok": True}
+
+
+@router.post("/api/audio-effects/mappings/{mapping_id}/activate")
+def activate_audio_effect_mapping(mapping_id: int, data: dict = Body(default_factory=dict)):
+    try:
+        provider_id = data.get("provider_id") if "provider_id" in data else data.get("providerId")
+        mapping = appstate.audio_effect_mappings.activate(mapping_id, provider_id="" if provider_id is None else provider_id)
+    except ValueError as exc:
+        return _audio_effects_error(exc)
+    if not mapping:
+        return JSONResponse({"error": "mapping not found"}, status_code=404)
+    return {"ok": True, "mapping": mapping}
+
+
+@router.delete("/api/audio-effects/active-mapping")
+def clear_audio_effect_active_mapping(song_key: str = Query(...), tone_key: str = Query("")):
+    try:
+        cleared = appstate.audio_effect_mappings.clear_active(song_key=song_key, tone_key=tone_key)
+    except ValueError as exc:
+        return _audio_effects_error(exc)
+    return {"ok": True, "cleared": cleared}

lib/routers/chart.py

@@ -0,0 +1,115 @@
+"""Chart-level endpoints — split/unsplit a chart from its work, resolve work
+membership, and the context-menu "Get info" file inspector.
+
+Extracted verbatim from ``server.py`` (R3); edits: ``@app`` -> ``@router``,
+``meta_db`` -> ``appstate.meta_db``. DLC path resolution comes from
+``dlc_paths``; sloppak/loose detection from the shared lib modules.
+"""
+
+from fastapi import APIRouter, HTTPException
+
+import appstate
+from dlc_paths import _get_dlc_dir, _resolve_dlc_path
+import sloppak as sloppak_mod
+import loosefolder as loosefolder_mod
+
+router = APIRouter()
+
+
+@router.post("/api/chart/{filename:path}/split")
+def api_split_chart(filename: str):
+    """'These aren't the same song' — split this chart out as its own singleton
+    work. Under /api/chart (NOT /api/song) so the DELETE /api/song/{path}
+    catch-all can't shadow it."""
+    key = appstate.meta_db._canonical_song_filename(filename)
+    appstate.meta_db.split_chart(key)
+    return {"ok": True, "filename": key}
+
+
+@router.post("/api/chart/{filename:path}/unsplit")
+def api_unsplit_chart(filename: str):
+    """Undo a split — rejoin the chart to its work."""
+    key = appstate.meta_db._canonical_song_filename(filename)
+    appstate.meta_db.unsplit_chart(key)
+    return {"ok": True, "filename": key}
+
+
+@router.get("/api/chart/{filename:path}/work")
+def api_get_chart_work(filename: str):
+    """Resolve a chart's work membership: {work_key, chart_count}. For openers
+    on rows that came from an ungrouped query (the tree view) — grouped grid
+    rows already carry both fields inline."""
+    return appstate.meta_db.chart_work(filename)
+
+
+@router.get("/api/chart/{filename:path}/fileinfo")
+def api_chart_fileinfo(filename: str):
+    """The context menu's "Get info": where the file lives + what the pack
+    contains. Under /api/chart — the GET /api/song/{path} catch-all would
+    swallow a /api/song/…/fileinfo suffix. Read-only; demo-mode blocks it
+    because it exposes filesystem paths."""
+    dlc = _get_dlc_dir()
+    if not dlc:
+        raise HTTPException(status_code=404, detail="not configured")
+    p = _resolve_dlc_path(dlc, filename)
+    if p is None:
+        raise HTTPException(status_code=403, detail="forbidden")
+    if not p.exists():
+        raise HTTPException(status_code=404, detail="not found")
+    # Restrict to actual charts — sloppak or loose song. Without this the route
+    # would stat ANY file the user happens to keep under DLC_DIR (e.g. notes),
+    # leaking its path/size; the app only recognises these two song formats.
+    is_pak = sloppak_mod.is_sloppak(p)
+    is_loose = loosefolder_mod.is_loose_song(p)
+    if not (is_pak or is_loose):
+        raise HTTPException(status_code=404, detail="not a chart")
+    st = p.stat()
+    info = {
+        "filename": filename,
+        "path": str(p),
+        "folder": str(p.parent),
+        "format": "sloppak" if is_pak else "loose",
+        # Directory-form songs report the tree's total (covers loose folders
+        # and dir-form paks); zip-form paks report the archive size. Symlinked
+        # entries are skipped so a link inside the folder can't pull in — or
+        # leak the size of — a file outside it.
+        "size": (st.st_size if p.is_file()
+                 else sum(f.stat().st_size for f in p.rglob("*")
+                          if f.is_file() and not f.is_symlink())),
+        "mtime": st.st_mtime,
+    }
+    if is_pak:
+        try:
+            m = sloppak_mod.load_manifest(p) or {}
+        except Exception:
+            m = {}
+        arrs = [str(a.get("name", a.get("id", ""))) for a in (m.get("arrangements") or [])
+                if isinstance(a, dict)]
+        stems = [str(s.get("id", "")) for s in (m.get("stems") or []) if isinstance(s, dict)]
+        try:
+            has_cover = sloppak_mod.read_cover_bytes(p, m) is not None
+        except Exception:
+            has_cover = False
+        # The optional identity/catalog keys, listed only when present — the
+        # Get-info panel's "what this pack carries vs what's missing" readout.
+        identity = {k: m.get(k) for k in
+                    ("mbid", "isrc", "genres", "track", "disc", "album_artist",
+                     "feedpak_version", "language")
+                    if m.get(k) not in (None, "", [])}
+        info["manifest"] = {
+            "title": str(m.get("title", "")), "artist": str(m.get("artist", "")),
+            "album": str(m.get("album", "")), "year": str(m.get("year", "") or ""),
+            "arrangements": arrs, "stems": stems,
+            "has_cover": has_cover, "has_lyrics": bool(m.get("lyrics")),
+            "authors": [a.get("name", "") if isinstance(a, dict) else str(a)
+                        for a in (m.get("authors") or [])],
+            "identity": identity,
+        }
+    # The enrichment verdict, so Get info can say "Matched (auto, 96%)" /
+    # "Pinned by you" / "Not matched" alongside the file facts.
+    row = appstate.meta_db.get_enrichment(filename)
+    if row:
+        info["match"] = {k: row.get(k) for k in
+                         ("match_state", "match_source", "match_score",
+                          "canon_artist", "canon_title", "canon_album", "canon_year")}
+    return info

lib/routers/loops.py

@@ -0,0 +1,60 @@
+"""Practice loops — saved A/B regions per song.
+
+Extracted verbatim from ``server.py`` (R3); only the decorator receiver
+(``@app`` -> ``@router``) and the singleton reads (``meta_db`` ->
+``appstate.meta_db``) changed. See ``appstate.py`` for why the reads stay
+module attributes.
+"""
+
+from fastapi import APIRouter
+
+import appstate
+
+router = APIRouter()
+
+
+@router.get("/api/loops")
+def list_loops(filename: str):
+    # Hold the DB lock for the read: the shared single connection
+    # (check_same_thread=False) is serialized through meta_db._lock by every
+    # writer, so an unlocked SELECT here can overlap a POST/DELETE commit.
+    db = appstate.meta_db
+    with db._lock:
+        rows = db.conn.execute(
+            "SELECT id, name, start_time, end_time FROM loops WHERE filename = ? ORDER BY start_time",
+            (filename,)
+        ).fetchall()
+    return [{"id": r[0], "name": r[1], "start": r[2], "end": r[3]} for r in rows]
+
+
+@router.post("/api/loops")
+def save_loop(data: dict):
+    filename = data.get("filename", "")
+    name = data.get("name", "").strip()
+    start = data.get("start")
+    end = data.get("end")
+    if not filename or start is None or end is None:
+        return {"error": "Missing fields"}
+    db = appstate.meta_db
+    with db._lock:
+        # COUNT + INSERT under one lock so two unnamed POSTs can't read the same
+        # count and both mint "Loop N" (the count is only used to name the row).
+        if not name:
+            count = db.conn.execute(
+                "SELECT COUNT(*) FROM loops WHERE filename = ?", (filename,)
+            ).fetchone()[0]
+            name = f"Loop {count + 1}"
+        db.conn.execute(
+            "INSERT INTO loops (filename, name, start_time, end_time) VALUES (?, ?, ?, ?)",
+            (filename, name, float(start), float(end))
+        )
+        db.conn.commit()
+    return {"ok": True, "name": name}
+
+
+@router.delete("/api/loops/{loop_id}")
+def delete_loop(loop_id: int):
+    with appstate.meta_db._lock:
+        appstate.meta_db.conn.execute("DELETE FROM loops WHERE id = ?", (loop_id,))
+        appstate.meta_db.conn.commit()
+    return {"ok": True}

lib/routers/playlists.py

@@ -0,0 +1,267 @@
+"""Playlists + custom playlist covers (fee[dB]ack v0.3.0).
+
+Extracted verbatim from ``server.py`` (R3). Edits: ``@app`` -> ``@router``,
+``meta_db`` -> ``appstate.meta_db``, ``CONFIG_DIR`` -> ``appstate.config_dir``
+(both read at call time through the seam), and ``_clean_str`` now imports from
+``reqfields``. See ``appstate.py``.
+"""
+
+import logging
+import os
+import tempfile
+from pathlib import Path
+
+from fastapi import APIRouter
+from fastapi.responses import FileResponse, JSONResponse
+
+import appstate
+from reqfields import _clean_str
+
+log = logging.getLogger("feedBack.server")
+
+router = APIRouter()
+
+# Cache policy for the custom-cover file response: revalidate every time so a
+# replaced cover is never served stale (pairs with the mtime-ns URL token).
+_ART_CACHE_HEADERS = {"Cache-Control": "no-cache"}
+
+
+def _playlist_cover_path(pid) -> Path | None:
+    """Filesystem path of a playlist's optional custom cover image (PNG),
+    stored under CONFIG_DIR. Returns None for a non-integer id."""
+    try:
+        pid = int(pid)
+    except (TypeError, ValueError):
+        return None
+    return appstate.config_dir / "playlist_covers" / f"{pid}.png"
+
+
+def _playlist_cover_url(pid) -> str | None:
+    cover = _playlist_cover_path(pid)
+    if not cover or not cover.exists():
+        return None
+    try:
+        # Nanosecond mtime so a same-second replace/remove/re-upload still
+        # changes the cache-bust token (int seconds could collide → stale image).
+        mt = cover.stat().st_mtime_ns
+    except OSError:
+        mt = 0
+    return f"/api/playlists/{pid}/cover?v={mt}"
+
+
+@router.get("/api/playlists")
+def api_list_playlists():
+    lists = appstate.meta_db.list_playlists()
+    for pl in lists:
+        pl["cover_url"] = _playlist_cover_url(pl["id"])
+    return lists
+
+
+@router.post("/api/playlists")
+def api_create_playlist(data: dict):
+    name = _clean_str(data.get("name"))
+    if not (1 <= len(name) <= 100):
+        return JSONResponse({"error": "Playlist name must be 1–100 characters."}, status_code=400)
+    # kind='album' = a curated album (§7.2): hand-picked works, a chosen chart
+    # per slot, played front-to-back on the queue. Absent/None = a regular mix.
+    kind = _clean_str(data.get("kind")) or None
+    if kind not in (None, "album"):
+        return JSONResponse({"error": "kind must be 'album' or omitted"}, status_code=400)
+    return appstate.meta_db.create_playlist(name, kind=kind)
+
+
+@router.get("/api/playlists/{pid}")
+def api_get_playlist(pid: int):
+    pl = appstate.meta_db.get_playlist(pid)
+    if pl is None:
+        return JSONResponse({"error": "not found"}, status_code=404)
+    pl["cover_url"] = _playlist_cover_url(pid)
+    return pl
+
+
+@router.patch("/api/playlists/{pid}")
+def api_rename_playlist(pid: int, data: dict):
+    pl = appstate.meta_db.get_playlist(pid)
+    if pl is None:
+        return JSONResponse({"error": "not found"}, status_code=404)
+    if pl["system_key"]:
+        return JSONResponse({"error": "System playlists cannot be renamed."}, status_code=400)
+    name = _clean_str(data.get("name"))
+    if not (1 <= len(name) <= 100):
+        return JSONResponse({"error": "Playlist name must be 1–100 characters."}, status_code=400)
+    appstate.meta_db.rename_playlist(pid, name)
+    return appstate.meta_db.get_playlist(pid)
+
+
+@router.delete("/api/playlists/{pid}")
+def api_delete_playlist(pid: int):
+    pl = appstate.meta_db.get_playlist(pid)
+    if pl is None:
+        return JSONResponse({"error": "not found"}, status_code=404)
+    if pl["system_key"]:
+        return JSONResponse({"error": "System playlists cannot be deleted."}, status_code=400)
+    if not appstate.meta_db.delete_playlist(pid):   # vanished under us (concurrent delete)
+        return JSONResponse({"error": "not found"}, status_code=404)
+    cover = _playlist_cover_path(pid)       # drop any custom cover with the playlist
+    if cover and cover.exists():
+        try:
+            cover.unlink()
+        except OSError:
+            pass
+    return {"ok": True}
+
+
+@router.post("/api/playlists/{pid}/songs")
+def api_add_playlist_song(pid: int, data: dict):
+    if appstate.meta_db.get_playlist(pid) is None:
+        return JSONResponse({"error": "not found"}, status_code=404)
+    filename = _clean_str(data.get("filename"))
+    if not filename:
+        return JSONResponse({"error": "filename required"}, status_code=400)
+    if appstate.meta_db.add_playlist_song(pid, filename) is None:   # playlist vanished under us
+        return JSONResponse({"error": "not found"}, status_code=404)
+    pl = appstate.meta_db.get_playlist(pid)
+    return pl if pl is not None else JSONResponse({"error": "not found"}, status_code=404)
+
+
+@router.patch("/api/playlists/{pid}/songs/{filename:path}")
+def api_update_playlist_slot(pid: int, filename: str, data: dict):
+    """Edit one curated-album slot: {"arrangement": name|null} pins/clears the
+    slot's arrangement; {"chart_filename": fn} swaps the slot to another chart
+    of the same work (position + pin kept). Albums only — a mix has no slots."""
+    pl = appstate.meta_db.get_playlist(pid)
+    if pl is None:
+        return JSONResponse({"error": "not found"}, status_code=404)
+    if pl.get("kind") != "album":
+        return JSONResponse({"error": "Slot editing is for albums."}, status_code=400)
+    kwargs = {}
+    if "chart_filename" in data:
+        new_fn = _clean_str(data.get("chart_filename"))
+        if not new_fn:
+            return JSONResponse({"error": "chart_filename must be a filename"}, status_code=400)
+        kwargs["new_filename"] = new_fn
+    if "arrangement" in data:
+        arr = data.get("arrangement")
+        if arr is not None and not (isinstance(arr, str) and 1 <= len(arr.strip()) <= 100):
+            return JSONResponse({"error": "arrangement must be a name or null"}, status_code=400)
+        kwargs["arrangement"] = arr.strip() if isinstance(arr, str) else None
+    if not kwargs:
+        return JSONResponse({"error": "nothing to update"}, status_code=400)
+    if appstate.meta_db.update_playlist_slot(pid, filename, **kwargs) is None:
+        return JSONResponse(
+            {"error": "no such slot, or the chart isn't a version of this song"},
+            status_code=400)
+    return appstate.meta_db.get_playlist(pid)
+
+
+@router.delete("/api/playlists/{pid}/songs/{filename:path}")
+def api_remove_playlist_song(pid: int, filename: str):
+    if appstate.meta_db.get_playlist(pid) is None:
+        return JSONResponse({"error": "not found"}, status_code=404)
+    appstate.meta_db.remove_playlist_song(pid, filename)
+    pl = appstate.meta_db.get_playlist(pid)
+    return pl if pl is not None else JSONResponse({"error": "not found"}, status_code=404)
+
+
+@router.post("/api/playlists/{pid}/reorder")
+def api_reorder_playlist(pid: int, data: dict):
+    pl = appstate.meta_db.get_playlist(pid)
+    if pl is None:
+        return JSONResponse({"error": "not found"}, status_code=404)
+    order = data.get("order")
+    if not isinstance(order, list) or not all(isinstance(f, str) for f in order):
+        return JSONResponse({"error": "order must be a list of filenames"}, status_code=400)
+    # Require an exact permutation of the playlist's current songs: a list with
+    # duplicates, omissions, or extras would otherwise produce duplicate
+    # positions / a partial reorder while still returning 200.
+    current = [s["filename"] for s in pl["songs"]]
+    if len(order) != len(current) or sorted(order) != sorted(current):
+        return JSONResponse(
+            {"error": "order must be a permutation of the playlist's current songs"},
+            status_code=400,
+        )
+    appstate.meta_db.reorder_playlist(pid, order)
+    return appstate.meta_db.get_playlist(pid)
+
+
+@router.post("/api/playlists/{pid}/cover")
+async def api_set_playlist_cover(pid: int, data: dict):
+    """Set a playlist's custom cover from a base64 / data-URL image (PNG/JPG).
+    Overrides the content-dependent (song-art) cover. Stored as a small PNG
+    thumbnail under CONFIG_DIR/playlist_covers/."""
+    if appstate.meta_db.get_playlist(pid) is None:
+        return JSONResponse({"error": "not found"}, status_code=404)
+    import base64
+    import io
+    b64 = data.get("image", "")
+    # Guard the type before the `","` membership test — a non-string image
+    # (e.g. {"image": 123} / null) would otherwise raise TypeError → 500.
+    # Mirrors the avatar/song-art upload guard.
+    if not isinstance(b64, str) or not b64:
+        return JSONResponse({"error": "No image data"}, status_code=400)
+    if "," in b64:
+        b64 = b64.split(",", 1)[1]
+    if not b64:
+        return JSONResponse({"error": "No image data"}, status_code=400)
+    try:
+        img_data = base64.b64decode(b64)
+    except Exception:
+        return JSONResponse({"error": "Invalid base64"}, status_code=400)
+    cover = _playlist_cover_path(pid)
+    cover.parent.mkdir(parents=True, exist_ok=True)
+    # Decode/validate the image — a bad payload is a CLIENT error (400), and the
+    # message stays generic so it can't echo internals.
+    try:
+        from PIL import Image
+        img = Image.open(io.BytesIO(img_data)).convert("RGB")
+        img.thumbnail((640, 640))                  # covers stay small
+    except Exception:
+        return JSONResponse({"error": "Invalid image"}, status_code=400)
+    # Persist. A save/replace failure is a SERVER error (500, logged, no
+    # filesystem detail leaked) — the pre-split handler mislabeled these as 400
+    # and echoed the exception. A unique temp name in the cover dir (not a shared
+    # `{pid}.png.tmp`) means two concurrent uploads can't clobber each other's
+    # temp file; the atomic replace publishes. Re-check the playlist still exists
+    # just before publishing so a delete that raced the decode above can't leave
+    # an orphan cover — cheap belt-and-braces; FeedBack is single-user
+    # (Principle I), so a full per-playlist lock would be for a race the
+    # deployment model precludes.
+    tmp = None
+    try:
+        # mkstemp is inside the try too: an unwritable dir / full disk raises
+        # here, and that's the same class of persistence failure as save/replace.
+        fd, tmp_name = tempfile.mkstemp(prefix=f".{pid}.", suffix=".png.tmp", dir=str(cover.parent))
+        tmp = Path(tmp_name)
+        with os.fdopen(fd, "wb") as f:
+            img.save(f, "PNG")
+        if appstate.meta_db.get_playlist(pid) is None:
+            tmp.unlink(missing_ok=True)
+            return JSONResponse({"error": "not found"}, status_code=404)
+        tmp.replace(cover)
+    except Exception:
+        if tmp is not None:
+            tmp.unlink(missing_ok=True)
+        log.exception("playlist cover save failed (pid=%s)", pid)
+        return JSONResponse({"error": "could not save cover"}, status_code=500)
+    return {"ok": True, "cover_url": _playlist_cover_url(pid)}
+
+
+@router.get("/api/playlists/{pid}/cover")
+def api_get_playlist_cover(pid: int):
+    cover = _playlist_cover_path(pid)
+    if not cover or not cover.exists():
+        return JSONResponse({"error": "not found"}, status_code=404)
+    # no-cache (revalidate) like song art, so a replaced cover is never served
+    # stale — pairs with the mtime-ns cache-bust token on the URL.
+    return FileResponse(str(cover), media_type="image/png", headers=_ART_CACHE_HEADERS)
+
+
+@router.delete("/api/playlists/{pid}/cover")
+def api_delete_playlist_cover(pid: int):
+    cover = _playlist_cover_path(pid)
+    if cover and cover.exists():
+        try:
+            cover.unlink()
+        except OSError:
+            pass
+    return {"ok": True}

lib/routers/wanted.py

@@ -0,0 +1,45 @@
+"""Wishlist / "wanted" API (feedBack#636) — songs the user wants but doesn't own.
+
+Extracted verbatim from ``server.py`` (R3); edits: ``@app`` -> ``@router``,
+``meta_db`` -> ``appstate.meta_db``, ``_clean_str`` from ``reqfields``.
+"""
+
+from fastapi import APIRouter
+from fastapi.responses import JSONResponse
+
+import appstate
+from reqfields import _clean_str
+
+router = APIRouter()
+
+
+@router.get("/api/wanted")
+def api_list_wanted():
+    """The wishlist — songs the user wants but doesn't own yet (newest first)."""
+    return {"wanted": appstate.meta_db.list_wanted()}
+
+
+@router.post("/api/wanted")
+def api_add_wanted(data: dict):
+    """Add a not-owned song to the wishlist. `artist`/`title` are required (at
+    least one non-empty); `source`/`source_ref`/`note` are optional. Idempotent
+    on identity so producers (find_more ownership-diff, manual add) can re-post."""
+    if not isinstance(data, dict):
+        return JSONResponse({"error": "body must be an object"}, status_code=400)
+    artist = _clean_str(data.get("artist"))
+    title = _clean_str(data.get("title"))
+    if not artist and not title:
+        return JSONResponse({"error": "artist or title required"}, status_code=400)
+    row = appstate.meta_db.add_wanted(
+        artist=artist, title=title,
+        source=_clean_str(data.get("source")) or "manual",
+        source_ref=_clean_str(data.get("source_ref")),
+        note=_clean_str(data.get("note")),
+    )
+    return {"ok": True, "wanted": row}
+
+
+@router.delete("/api/wanted/{wanted_id}")
+def api_remove_wanted(wanted_id: int):
+    """Remove a wishlist entry by id."""
+    return {"ok": appstate.meta_db.remove_wanted(wanted_id)}

lib/scan_worker.py

@@ -3,7 +3,7 @@
 This module is deliberately kept apart from ``server.py`` so that
 ``ProcessPoolExecutor`` workers can import and unpickle ``_scan_one``
 without dragging in ``server.py``'s import-time side effects
-(``configure_logging()``, ``meta_db = MetadataDB()`` opening/migrating
+(``configure_logging()``, ``meta_db = MetadataDB(CONFIG_DIR)`` opening/migrating
 SQLite, and ``register_plugin_api(app)`` registering routes).
 
 The background scan spawns its pool with the ``spawn`` start method (see

lib/tunings.py

@@ -98,6 +98,22 @@ def open_midis_to_freqs(midis: list[int], reference_pitch: float = DEFAULT_REFER
     return [round(midi_to_freq(m, reference_pitch), 2) for m in midis]
 
 
+def freqs_to_midis(freqs: list[float], reference_pitch: float = DEFAULT_REFERENCE_PITCH) -> list[int] | None:
+    """Return absolute open-string MIDI notes for frequencies at the supplied
+    A4 reference — the inverse of open_midis_to_freqs. None if any entry is
+    non-numeric or non-positive (a provider could hand us anything)."""
+    out: list[int] = []
+    for f in freqs:
+        try:
+            f = float(f)
+        except (TypeError, ValueError):
+            return None
+        if f <= 0:
+            return None
+        out.append(int(round(69 + 12 * math.log2(f / reference_pitch))))
+    return out
+
+
 def tuning_offsets_from_midis(instrument_key: str, midis: list[int]) -> list[int] | None:
     """Return semitone offsets from the instrument's standard open strings."""
     standard = STANDARD_OPEN_MIDIS.get(instrument_key)

package.json

@@ -8,9 +8,12 @@
     "test:headed": "playwright test --headed",
     "test:debug": "playwright test --debug",
     "test:js": "node --test tests/js/*.test.js 'tests/plugins/*/js/*.test.js'",
-    "install:playwright": "playwright install chromium"
+    "install:playwright": "playwright install chromium",
+    "lint": "eslint ."
   },
   "devDependencies": {
-    "@playwright/test": "^1.59.1"
+    "@playwright/test": "^1.59.1",
+    "eslint": "^9.39.4",
+    "eslint-plugin-import-x": "^4.17.1"
   }
 }

plugins/__init__.py

@@ -18,6 +18,54 @@ from safepath import safe_join
 log = logging.getLogger("feedBack.plugins")
 
 
+def _plugin_media_type(path: Path) -> str:
+    """Best-effort Content-Type for a served plugin file. `.js`/`.css` must come
+    back as JavaScript/CSS so `<script type=module>` / `addModule()` / a `<link>`
+    accept them; `mimetypes.guess_type` can miss these on a stripped platform
+    registry, so fall back explicitly (mirrors the assets/ route)."""
+    media_type = mimetypes.guess_type(path.name)[0]
+    if media_type is None and path.suffix == ".js":
+        return "application/javascript"
+    if media_type is None and path.suffix == ".css":
+        return "text/css"
+    return media_type or "application/octet-stream"
+
+
+def _plugin_file_etag(path: Path) -> str | None:
+    """Weak ETag from mtime+size — cheap, stable across reads, changes on edit.
+    This is what makes the live-edit loop work for module graphs: a conditional
+    GET revalidates and 304s unchanged files on refresh instead of re-downloading
+    the whole `src/` tree. Returns None if the file can't be stat'd."""
+    try:
+        st = path.stat()
+    except OSError:
+        return None
+    return f'W/"{st.st_mtime_ns:x}-{st.st_size:x}"'
+
+
+def _if_none_match(request: Request, etag: str) -> bool:
+    """True when the client's If-None-Match already holds `etag`."""
+    # ponytail: we serve one weak ETag; the browser echoes it back verbatim, so
+    # a direct compare is enough (comma-split tolerates a proxy concatenation).
+    return etag in [t.strip() for t in request.headers.get("if-none-match", "").split(",")]
+
+
+def _plugin_file_response(request: Request, path: Path, media_type: str) -> Response:
+    """Serve a plugin source/asset file with the live-edit cache contract:
+    `Cache-Control: no-cache` (browser may store but MUST revalidate) + a weak
+    ETag, and a bodyless 304 when the client's If-None-Match already matches.
+    Starlette's `FileResponse` emits an ETag but never evaluates If-None-Match
+    itself, so the conditional handling has to live here."""
+    headers = {"Cache-Control": "no-cache"}
+    etag = _plugin_file_etag(path)
+    if etag:
+        headers["ETag"] = etag
+        if _if_none_match(request, etag):
+            return Response(status_code=304, headers=headers)
+    # FileResponse sets etag/last-modified via setdefault, so the ETag above wins.
+    return FileResponse(path, media_type=media_type, headers=headers)
+
+
 PLUGINS_DIR = Path(__file__).parent
 # Holds only *ready* (loaded) plugins — those whose dependencies installed
 # and whose routes registered. A plugin GRADUATES from PENDING_PLUGINS into
@@ -1373,6 +1421,12 @@ def load_plugins(app: FastAPI, context: dict, progress_cb=None, route_setup_fn=N
             "version": manifest.get("version"),
             "has_screen": bool(manifest.get("screen")),
             "has_script": bool(manifest.get("script")),
+            # Module-migration (R0): `scriptType:"module"` tells the loader to
+            # inject screen.js as <script type="module">; `minHost` is the
+            # min core version a migrated plugin needs (passthrough only in R0 —
+            # enforcement is deferred to R4, master §4b). None when unset.
+            "script_type": manifest.get("scriptType"),
+            "min_host": manifest.get("minHost"),
             "has_settings": bool(manifest.get("settings")),
             "settings_category": _settings_category,
             # Drives the v3 shell's immersive (full-screen) mode for this
@@ -2089,6 +2143,11 @@ def register_plugin_api(app: FastAPI):
                 "fallback": p.get("fallback", False),
                 "has_screen": p["has_screen"],
                 "has_script": p["has_script"],
+                # Module-migration passthrough (R0). Re-read from the manifest
+                # like `version` above so stubbed test entries (built without
+                # _nav_entry) don't need the key.
+                "script_type": (p.get("_manifest") or {}).get("scriptType"),
+                "min_host": (p.get("_manifest") or {}).get("minHost"),
                 "has_settings": p["has_settings"],
                 # v3 immersive screen opt-in (full-screen plugin UI).
                 "fullscreen": p.get("fullscreen", False),
@@ -2142,6 +2201,9 @@ def register_plugin_api(app: FastAPI):
                 "fallback": False,
                 "has_screen": e.get("has_screen", False),
                 "has_script": e.get("has_script", False),
+                # Pending entries come from _nav_entry, so they carry these.
+                "script_type": e.get("script_type"),
+                "min_host": e.get("min_host"),
                 "has_settings": e.get("has_settings", False),
                 "settings_category": e.get("settings_category"),
                 "fullscreen": e.get("fullscreen", False),
@@ -2307,7 +2369,7 @@ def register_plugin_api(app: FastAPI):
         return HTMLResponse("", status_code=404)
 
     @app.get("/api/plugins/{plugin_id}/screen.js")
-    def plugin_screen_js(plugin_id: str):
+    def plugin_screen_js(request: Request, plugin_id: str):
         with PLUGINS_LOCK:
             snapshot = list(LOADED_PLUGINS)
         for p in snapshot:
@@ -2315,8 +2377,11 @@ def register_plugin_api(app: FastAPI):
                 if p.get("status", "ready") != "ready":
                     break
                 script_file = p["_dir"] / p["_manifest"].get("script", "screen.js")
-                if script_file.exists():
-                    return Response(script_file.read_text(encoding="utf-8"), media_type="application/javascript")
+                if script_file.is_file():
+                    # no-cache + ETag/304 so an edited screen.js reloads on
+                    # refresh while an unchanged one revalidates cheaply — the
+                    # same live-edit contract the src/ module graph relies on.
+                    return _plugin_file_response(request, script_file, "application/javascript")
         return Response("", status_code=404)
 
     @app.get("/api/plugins/{plugin_id}/settings.html")
@@ -2377,7 +2442,7 @@ def register_plugin_api(app: FastAPI):
         return Response("{}", status_code=404, media_type="application/json")
 
     @app.get("/api/plugins/{plugin_id}/assets/{asset_path:path}")
-    def plugin_asset(plugin_id: str, asset_path: str):
+    def plugin_asset(request: Request, plugin_id: str, asset_path: str):
         """Serve a static file a plugin bundles under its own ``assets/``
         directory (e.g. an AudioWorklet module, WASM, or image). Unlike the
         fixed screen.js/settings.html handlers above, this is a generic
@@ -2399,16 +2464,35 @@ def register_plugin_api(app: FastAPI):
                     log.warning("Plugin %r: asset path rejected: %r", plugin_id, asset_path)
                     break
                 if target.is_file():
-                    media_type = mimetypes.guess_type(target.name)[0]
-                    # .js must come back as JavaScript so addModule() / <script>
-                    # accept it; guess_type can miss this on some platforms.
-                    if media_type is None and target.suffix == ".js":
-                        media_type = "application/javascript"
-                    # .css must come back as text/css so a <link rel=stylesheet>
-                    # (the styles capability) is honoured; guess_type can miss it
-                    # on a stripped platform mimetypes registry, same as .js.
-                    elif media_type is None and target.suffix == ".css":
-                        media_type = "text/css"
-                    return FileResponse(target, media_type=media_type or "application/octet-stream")
+                    # no-cache + ETag/304 so a live-edited worklet/asset reloads
+                    # on refresh (bare FileResponse emits an ETag but never 304s).
+                    return _plugin_file_response(request, target, _plugin_media_type(target))
+                break
+        return Response("", status_code=404)
+
+    @app.get("/api/plugins/{plugin_id}/src/{src_path:path}")
+    def plugin_src(request: Request, plugin_id: str, src_path: str):
+        """Serve a file from a plugin's ES-module source tree under ``src/``.
+
+        This is the R0 host capability that lets a migrated plugin's
+        ``screen.js`` (a one-line ``import './src/main.js'``) load its whole
+        module graph. Containment mirrors the assets/ route exactly —
+        ``safe_join`` against ``<plugin>/src`` rejects ``..``, absolute paths,
+        and NUL bytes — and the live-edit cache contract (no-cache + ETag/304)
+        makes an edited module reload on refresh while unchanged ones 304.
+        Read-only; the src/ tree is source files, never executed server-side.
+        """
+        with PLUGINS_LOCK:
+            snapshot = list(LOADED_PLUGINS)
+        for p in snapshot:
+            if p["id"] == plugin_id:
+                if p.get("status", "ready") != "ready":
+                    break
+                target = safe_join(p["_dir"] / "src", src_path)
+                if target is None:
+                    log.warning("Plugin %r: src path rejected: %r", plugin_id, src_path)
+                    break
+                if target.is_file():
+                    return _plugin_file_response(request, target, _plugin_media_type(target))
                 break
         return Response("", status_code=404)

plugins/drum_highway_3d/plugin.json

@@ -1,7 +1,7 @@
 {
   "id": "drum_highway_3d",
   "name": "3D Drum Highway",
-  "version": "0.3.1",
+  "version": "0.3.2",
   "type": "visualization",
   "bundled": true,
   "script": "screen.js",

plugins/drum_highway_3d/screen.js

@@ -1361,6 +1361,41 @@
         } catch (_) { /* dispatch unavailable — persisted value applies next init */ }
     };
 
+    /* ======================================================================
+     *  Camera Director bridge resolver (pure — exported via createFactory.__test)
+     * ====================================================================== */
+
+    /**
+     * The active splitscreen API, defensive on the global-name rename in flight
+     * (feedBackSplitscreen is canonical; slopsmithSplitscreen is the legacy alias).
+     * @returns {object|null} the splitscreen API, or null when not present
+     */
+    function _ssApi() { return window.feedBackSplitscreen || window.slopsmithSplitscreen || null; }
+
+    /**
+     * Resolve the Camera Director camera for a canvas: this panel's camera under
+     * splitscreen, else the global, else null (Camera Director absent → stock
+     * framing). Throw-safe on panelIndexFor so a misbehaving splitscreen build
+     * can't break framing.
+     * @param {HTMLCanvasElement} canvas this renderer's highway canvas
+     * @param {object|null} ss the splitscreen API (see _ssApi)
+     * @param {object|null} panelsMap window.__h3dCamCtlPanels (per-panel cameras by index)
+     * @param {object|null} globalCam window.__h3dCamCtl (single global camera)
+     * @returns {object|null} the resolved free-camera bridge, or null
+     */
+    function _resolveFreeCam(canvas, ss, panelsMap, globalCam) {
+        if (panelsMap && ss && typeof ss.panelIndexFor === 'function') {
+            try {
+                const i = ss.panelIndexFor(canvas);
+                // Only a non-negative integer indexes the panel map — a non-int /
+                // negative / string index (or a prototype key) must not resolve an
+                // unintended/inherited property; fall through to the global then.
+                if (Number.isInteger(i) && i >= 0 && panelsMap[i]) return panelsMap[i];
+            } catch (e) { /* ignore */ }
+        }
+        return globalCam || null;
+    }
+
     /* ======================================================================
      *  Renderer factory
      * ====================================================================== */
@@ -1414,7 +1449,7 @@
         let _sparkPts = null, _sparkPos = null, _sparkCol = null, _sparkVel = null, _sparkLife = null;
         let _fxLastWall = 0;          // wall clock for FX integration (sparks, pulse decay)
         let _kickPulse = 0;           // kick-hit camera-dip + floor-wash envelope
-        let _camBaseH = 0, _camBaseD = 0;  // positionCamera's unpulsed pose
+        let _camBaseH = null, _camBaseD = null;  // positionCamera's unpulsed pose (null until it first runs; applyCamera's guard depends on this)
         let _gaussTex = null;         // shared soft-falloff texture for flash quads
         let _laneFlashQuads = [];     // pooled additive quad per hand lane (z=0)
         let _kickFlashQuad = null;    // full-width flash quad for the kick bar
@@ -2651,6 +2686,48 @@
             cam.lookAt(0, 0, -AHEAD * TS * 0.45);
         }
 
+        /**
+         * Camera Director bridge for THIS panel — delegates to the pure, unit-
+         * tested _resolveFreeCam / _ssApi (resolver block above the factory).
+         * Reads the live globals: per-panel map __h3dCamCtlPanels → this panel's
+         * camera, else the global __h3dCamCtl, else null (stock framing).
+         * @param {HTMLCanvasElement} canvas this panel's highway canvas
+         * @returns {object|null} the resolved free-camera bridge, or null
+         */
+        function _freeCamFor(canvas) {
+            return _resolveFreeCam(canvas, _ssApi(), window.__h3dCamCtlPanels, window.__h3dCamCtl);
+        }
+
+        // Per-frame camera write: static base pose (positionCamera) + kick-pulse Y
+        // dip, then layer Camera Director free-cam offsets (dolly/height/orbit on
+        // the camera-from-target vector; pan/pitch on the look target). Runs every
+        // frame so a live free-cam drag is smooth; allocation-free; NaN-safe; a
+        // null/disabled bridge reproduces the stock static+pulse pose exactly.
+        function applyCamera() {
+            if (_camBaseH == null) return;               // before first positionCamera()
+            const _dip = (_kickPulse > 0.001) ? (0.8 * K * _kickPulse * fx.hitFx) : 0;
+            let _cx = 0, _cy = _camBaseH - _dip, _cz = _camBaseD;
+            let _lx = 0, _ly = 0, _lz = -AHEAD * TS * 0.45;
+            const _fc = _freeCamFor(highwayCanvas);
+            if (_fc && _fc.enabled) {
+                const _dm = Number.isFinite(_fc.distMul) ? _fc.distMul : 1;
+                const _hm = Number.isFinite(_fc.heightMul) ? _fc.heightMul : 1;
+                const _yaw = Number.isFinite(_fc.yaw) ? _fc.yaw : 0;
+                let _vx = _cx - _lx, _vy = _cy - _ly, _vz = _cz - _lz;
+                _vx *= _dm; _vy *= _dm; _vz *= _dm;   // dolly (zoom)
+                _vy *= _hm;                            // height
+                const _cyw = Math.cos(_yaw), _syw = Math.sin(_yaw);
+                const _rx = _vx * _cyw - _vz * _syw, _rz = _vx * _syw + _vz * _cyw; // orbit around Y
+                _cx = _lx + _rx; _cy = _ly + _vy; _cz = _lz + _rz;
+                const _px = Number.isFinite(_fc.panX) ? _fc.panX : 0;
+                const _py = Number.isFinite(_fc.panY) ? _fc.panY : 0;
+                const _pt = Number.isFinite(_fc.pitch) ? _fc.pitch : 0;
+                _lx += _px * K; _ly += (_pt + _py) * K;
+            }
+            cam.position.set(_cx, _cy, _cz);
+            cam.lookAt(_lx, _ly, _lz);
+        }
+
         function buildLanes(_floorW, floorD) {
             laneGroup = new T.Group();
             laneStripeMats = [];
@@ -3431,15 +3508,18 @@
                             BG_STYLES[_bgState._style].update(_bgState.s, bands, fdt, nowMs / 1000);
                         } catch (_) { /* visual-only */ }
                     }
+                    // Kick pulse decays each frame; it drives the floor flash and,
+                    // via applyCamera(), the camera Y dip.
                     if (_kickPulse > 0.001) {
                         _kickPulse *= Math.exp(-fdt * 7);
-                        cam.position.y = _camBaseH - 0.8 * K * _kickPulse * fx.hitFx;
                         if (_floorFlash) _floorFlash.material.opacity = 0.25 * _kickPulse * fx.hitFx;
                     } else if (_kickPulse !== 0) {
                         _kickPulse = 0;
-                        cam.position.y = _camBaseH;
                         if (_floorFlash) _floorFlash.material.opacity = 0;
                     }
+                    // Write the camera every frame: static base pose + kick dip +
+                    // Camera Director free-cam offsets (per-panel-aware).
+                    applyCamera();
                 }
                 // Approach highlight: raise each lane stripe toward its next
                 // note (accumulated by the rebuildNotes walk above).
@@ -3565,6 +3645,8 @@
     // vm-loaded with no DOM/WebGL; everything here must stay side-effect
     // free to call).
     window.slopsmithViz_drum_highway_3d.__test = {
+        _resolveFreeCam,
+        _ssApi,
         _variantForHit,
         _classifyTiming,
         readFxSettings,

plugins/drum_highway_3d/tests/camera_bridge.test.js

@@ -0,0 +1,78 @@
+// Camera Director bridge resolver tests: per-panel select, global fallback,
+// null-when-absent, throw-safety, and the splitscreen global-name alias. Loads
+// screen.js in a bare vm window and exercises the __test exports (no DOM/WebGL).
+const { test } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+const vm = require('node:vm');
+
+function load() {
+    const window = {
+        console,
+        location: { protocol: 'http:', host: 'localhost' },
+        slopsmith: {},
+    };
+    window.window = window;
+    window.globalThis = window;
+    const context = vm.createContext(window);
+    const src = fs.readFileSync(path.join(__dirname, '..', 'screen.js'), 'utf8');
+    vm.runInContext(src, context, { filename: 'screen.js' });
+    return { window, __test: window.slopsmithViz_drum_highway_3d.__test };
+}
+
+test('_resolveFreeCam: per-panel camera under splitscreen', () => {
+    const { __test } = load();
+    const c0 = {}, c1 = {};
+    const ss = { panelIndexFor: (c) => (c === c0 ? 0 : 1) };
+    const map = { 0: { id: 'p0' }, 1: { id: 'p1' } };
+    assert.equal(__test._resolveFreeCam(c0, ss, map, { id: 'g' }).id, 'p0');
+    assert.equal(__test._resolveFreeCam(c1, ss, map, { id: 'g' }).id, 'p1');
+});
+
+test('_resolveFreeCam: falls back to global when there is no panel map', () => {
+    const { __test } = load();
+    const g = { id: 'global' };
+    assert.equal(__test._resolveFreeCam({}, { panelIndexFor: () => 0 }, null, g), g);
+});
+
+test('_resolveFreeCam: falls back to global when the panel has no map entry', () => {
+    const { __test } = load();
+    const g = { id: 'global' };
+    const ss = { panelIndexFor: () => 3 };            // index 3 absent from map
+    assert.equal(__test._resolveFreeCam({}, ss, { 0: {} }, g), g);
+});
+
+test('_resolveFreeCam: null when Camera Director is absent (no global)', () => {
+    const { __test } = load();
+    assert.equal(__test._resolveFreeCam({}, null, null, null), null);
+    assert.equal(__test._resolveFreeCam({}, { panelIndexFor: () => 0 }, {}, undefined), null);
+});
+
+test('_resolveFreeCam: throw-safe on panelIndexFor → falls back to global', () => {
+    const { __test } = load();
+    const g = { id: 'global' };
+    const ss = { panelIndexFor: () => { throw new Error('boom'); } };
+    assert.equal(__test._resolveFreeCam({}, ss, { 0: {} }, g), g);
+});
+
+test('_resolveFreeCam: NaN/negative/float/string index → falls back to global', () => {
+    const { __test } = load();
+    const g = { id: 'global' };
+    assert.equal(__test._resolveFreeCam({}, { panelIndexFor: () => NaN }, { 0: {} }, g), g);
+    assert.equal(__test._resolveFreeCam({}, { panelIndexFor: () => -1 }, { 0: {} }, g), g);
+    assert.equal(__test._resolveFreeCam({}, { panelIndexFor: () => 0.5 }, { 0: {} }, g), g);
+    // A string/prototype key must not resolve an inherited property (e.g. toString).
+    assert.equal(__test._resolveFreeCam({}, { panelIndexFor: () => 'toString' }, {}, g), g);
+});
+
+test('_ssApi: null when neither global set; slopsmith alias; feedBack canonical wins', () => {
+    const { window, __test } = load();
+    assert.equal(__test._ssApi(), null);
+    const legacy = { panelIndexFor: () => 0 };
+    window.slopsmithSplitscreen = legacy;
+    assert.equal(__test._ssApi(), legacy);            // legacy alias picked up
+    const current = { panelIndexFor: () => 1 };
+    window.feedBackSplitscreen = current;
+    assert.equal(__test._ssApi(), current);           // canonical name takes precedence
+});

plugins/highway_3d/plugin.json

@@ -1,7 +1,7 @@
 {
     "id": "highway_3d",
     "name": "3D Highway",
-    "version": "3.31.3",
+    "version": "3.31.5",
     "type": "visualization",
     "bundled": true,
     "script": "screen.js",

plugins/highway_3d/screen.js

@@ -548,9 +548,20 @@
             ctrl.ownsActx = !(fogAudio && fogAudio.ctx);
             ctrl.actx = (fogAudio && fogAudio.ctx) || new Ctx();
             if (ctrl.actx.state === 'suspended' && ctrl.actx.resume) ctrl.actx.resume().catch(() => {});
+            // Seed the DRAWING BUFFER (canvas.width/height) to the device-pixel
+            // render size and report that SAME size to Butterchurn. Its on-screen
+            // pass viewports to the reported size but never sizes the output canvas
+            // itself — leaving the buffer at the 300x150 default blits the whole
+            // visualizer into a corner that CSS then stretches across the highway.
+            // pixelRatio:1 because DPR is now folded into the reported size, so
+            // buffer == viewport == internal texsize (no double-counting).
+            const _bcRatio0 = Math.min(window.devicePixelRatio || 1, 1.5);
+            const _bcW0 = Math.max(1, Math.round((sz.w || 1280) * _bcRatio0));
+            const _bcH0 = Math.max(1, Math.round((sz.h || 720) * _bcRatio0));
+            canvas.width = _bcW0; canvas.height = _bcH0;
             ctrl.viz = bc.createVisualizer(ctrl.actx, canvas, {
-                width: sz.w || 1280, height: sz.h || 720,
-                pixelRatio: Math.min(window.devicePixelRatio || 1, 1.5), textureRatio: 1,
+                width: _bcW0, height: _bcH0,
+                pixelRatio: 1, textureRatio: 1,
             });
             if (_bcIsDesktop()) {
                 try {
@@ -584,6 +595,27 @@
             ctrl.actx = null; ctrl.viz = null; ctrl.dead = true;
             _bcControllers.delete(ctrl);
         });
+        // Size the Butterchurn output: set the canvas DRAWING BUFFER to the
+        // device-pixel render size AND report that same size, so buffer ==
+        // on-screen viewport == full fill. Butterchurn never sizes the output
+        // canvas itself; the previous code set only CSS size, leaving the buffer
+        // at the 300x150 default -> the viz showed a stretched lower-left corner
+        // (worse the larger the panel). Ratio reuses the highway's DPR budget.
+        function _bcApplySize(cssW, cssH) {
+            if (!(cssW > 0 && cssH > 0)) return;
+            ctrl.lastW = cssW; ctrl.lastH = cssH;
+            const ratio = Math.min(window.devicePixelRatio || 1, 1.5);
+            const bw = Math.max(1, Math.round(cssW * ratio)), bh = Math.max(1, Math.round(cssH * ratio));
+            if (canvas.width !== bw) canvas.width = bw;
+            if (canvas.height !== bh) canvas.height = bh;
+            const wpx = cssW + 'px', hpx = cssH + 'px';
+            // Confine ALL layers to exactly the highway-canvas rect so the opaque
+            // backdrop can't bleed over the transport bar above the highway.
+            [ctrl.canvas, ctrl.backdrop, ctrl.scrim, ctrl.tint].forEach((el) => {
+                if (el) { el.style.width = wpx; el.style.height = hpx; el.style.right = 'auto'; el.style.bottom = 'auto'; }
+            });
+            if (ctrl.viz && ctrl.viz.setRendererSize) { try { ctrl.viz.setRendererSize(bw, bh); } catch (e) {} }
+        }
         return {
             applySettings() { ctrl.applySettings(); },
             dead() { return ctrl.dead; },
@@ -612,18 +644,11 @@
                 if (!ctrl.viz || !s.enabled) return; // skip GPU work when the bg is off
                 const sz = sizeProvider && sizeProvider();
                 if (sz && sz.w > 0 && sz.h > 0 && (sz.w !== ctrl.lastW || sz.h !== ctrl.lastH)) {
-                    ctrl.lastW = sz.w; ctrl.lastH = sz.h;
-                    const wpx = sz.w + 'px', hpx = sz.h + 'px';
-                    // Confine ALL layers to exactly the highway-canvas rect so the opaque
-                    // backdrop can't bleed over the transport bar above the highway.
-                    [ctrl.canvas, ctrl.backdrop, ctrl.scrim, ctrl.tint].forEach((el) => {
-                        if (el) { el.style.width = wpx; el.style.height = hpx; el.style.right = 'auto'; el.style.bottom = 'auto'; }
-                    });
-                    try { ctrl.viz.setRendererSize(sz.w, sz.h); } catch (e) {}
+                    _bcApplySize(sz.w, sz.h);
                 }
                 try { ctrl.viz.render(); } catch (e) {}
             },
-            resize(w, h) { if (ctrl.viz && ctrl.viz.setRendererSize) { try { ctrl.viz.setRendererSize(w, h); } catch (e) {} ctrl.lastW = w; ctrl.lastH = h; } },
+            resize(w, h) { _bcApplySize(w, h); },
             destroy() {
                 ctrl.dead = true;
                 _bcControllers.delete(ctrl);
@@ -2595,10 +2620,51 @@
     }
     const FRET_NUMBER_GHOST_SCOPE_IDS = ['chords', 'all'];
 
+    /**
+     * localStorage panel key for per-panel background settings ('main' or
+     * 'panel<index>'). Defensive on the splitscreen global-name rename in flight,
+     * and throw-safe on panelIndexFor — same as _freeCamFor — so a misbehaving
+     * splitscreen build can't take down background-settings resolution. Only a
+     * non-negative integer index yields a 'panel<N>' key; anything else (null,
+     * NaN, negative, non-integer) falls back to 'main' so a bad index can never
+     * mint a bogus "panelNaN"-style key.
+     * @param {HTMLCanvasElement} canvas this renderer's highway canvas
+     * @returns {string} 'main' or 'panel<index>'
+     */
     function _bgPanelKey(canvas) {
-        const ss = window.feedBackSplitscreen;
-        const idx = (ss && typeof ss.panelIndexFor === 'function') ? ss.panelIndexFor(canvas) : null;
-        return (idx == null) ? 'main' : 'panel' + idx;
+        const ss = window.feedBackSplitscreen || window.slopsmithSplitscreen;
+        let idx = null;
+        if (ss && typeof ss.panelIndexFor === 'function') {
+            try { idx = ss.panelIndexFor(canvas); } catch (e) { idx = null; }
+        }
+        return (Number.isInteger(idx) && idx >= 0) ? 'panel' + idx : 'main';
+    }
+
+    /**
+     * Camera Director bridge resolver. Prefers THIS panel's per-panel camera under
+     * splitscreen (window.__h3dCamCtlPanels[panelIndex]) and falls back to the
+     * single global (window.__h3dCamCtl); returns null when Camera Director is
+     * absent → 100% stock framing. Defensive on the splitscreen global-name rename
+     * in flight (feedBackSplitscreen vs slopsmithSplitscreen); throw-safe on
+     * panelIndexFor. Mirrors the panel resolution in _bgPanelKey.
+     * @param {HTMLCanvasElement} canvas this renderer's highway canvas
+     * @returns {object|null} the resolved free-camera bridge, or null
+     */
+    function _freeCamFor(canvas) {
+        const map = window.__h3dCamCtlPanels;
+        if (map) {
+            const ss = window.feedBackSplitscreen || window.slopsmithSplitscreen;
+            if (ss && typeof ss.panelIndexFor === 'function') {
+                try {
+                    const i = ss.panelIndexFor(canvas);
+                    // Only a non-negative integer indexes the map (same hardening
+                    // as _bgPanelKey) — a non-int / negative / string index must not
+                    // resolve an unintended/inherited property; fall through then.
+                    if (Number.isInteger(i) && i >= 0 && map[i]) return map[i];
+                } catch (e) { /* ignore */ }
+            }
+        }
+        return window.__h3dCamCtl || null;
     }
     // In-memory fallback for when localStorage is blocked (private mode,
     // sandboxed iframes, some test runners). _bgWriteGlobal stages the
@@ -14664,7 +14730,10 @@
             // suppressed while the Camera Director owns the view (it wins).
             const _startAspect = (_tune && Number.isFinite(_tune.startAspect) && _tune.startAspect > 0)
                 ? _tune.startAspect : HORPLUS_START_ASPECT;
-            const _dirActive = !!(window.__h3dCamCtl && window.__h3dCamCtl.enabled);
+            // Resolve the Camera Director bridge once (per-panel under splitscreen,
+            // else global). Used both for the wide-pane gate and the transforms below.
+            const _freeCam = _freeCamFor(highwayCanvas);
+            const _dirActive = !!(_freeCam && _freeCam.enabled);
             const _wide = !!(_tune && _paneAspect > _startAspect) && !_dirActive;
             const _poseHMul = (_wide && Number.isFinite(_tune.heightMul)) ? _tune.heightMul : 1;
             const _poseDMul = (_wide && Number.isFinite(_tune.distMul)) ? _tune.distMul : 1;
@@ -14691,13 +14760,16 @@
             if (_poseHMul !== 1) _camY *= _poseHMul;
             if (_poseDMul !== 1) _camZ *= _poseDMul;
             // ── Free-camera user tweaks (orbit / height / zoom / pan) ──
-            // Driven by the Camera Director plugin via window.__h3dCamCtl.
+            // Driven by the Camera Director plugin via the camera bridge:
+            // window.__h3dCamCtlPanels[panelIndexFor(canvas)] when split (this
+            // panel's own camera), falling back to the global window.__h3dCamCtl.
             // Layered ON TOP of the auto-framing so note tracking still works.
             // The bridge is read once into _freeCam and reused for both the
             // position and the look-at transforms; every field is coerced to a
             // finite number before use so a malformed object can never feed NaN
             // into cam.position / cam.lookAt.
-            const _freeCam = window.__h3dCamCtl;
+            // _freeCam resolved above via _freeCamFor(highwayCanvas): the
+            // per-panel __h3dCamCtlPanels entry, else global __h3dCamCtl, else null.
             const _lookAtZ = -FOCUS_D * 0.35 * _poseLookZMul;
             if (_freeCam && _freeCam.enabled) {
                 const _distMul = Number.isFinite(_freeCam.distMul) ? _freeCam.distMul : 1;

plugins/keys_highway_3d/README.md

@@ -3,13 +3,34 @@
 RS+-style falling-note 3D piano highway for [Slopsmith](https://github.com/got-feedback/feedback), fed by the **Sloppak Notation Format** (sloppak-spec §5.3) — part of the piano/keys first-class epic (slopsmith#828, plugin workstream slopsmith#824).
 
 - Consumes the `notation_info` / `notation_measures` highway-WS stream over a private per-instance socket and flattens measure → staff → voice → beat → note into `{midi, t, durSec, hand}` (durations derived from written `dur`/`dot`/`tu` at the running tempo; ties extend; overlap-clamped).
-- 3D perspective highway to a vanishing point with a real white/black-key keyboard; per-key **pitch-class colours** (Synthesia convention — C red, D yellow, E blue, …) with hand (rh/lh) as a secondary brightness cue. Selectable **note-colour palettes** (settings → Note colours, `keys3d_bg_palette`, default the per-octave scheme): a per-octave rainbow (each octave its own hue, darker sharps), the original per-pitch "Rainbow" table, vivid/pastel per-pitch variants, and single-hue two-tone palettes (uniform naturals, darker sharps) for players who want "black key coming" to read at a glance; notes, key glow, lane guides and hit flames all follow the pick live.
+- 3D perspective highway to a vanishing point with a real white/black-key keyboard; per-key **pitch-class colors** (Synthesia convention — C red, D yellow, E blue, …) with hand (rh/lh) as a secondary brightness cue. Selectable **note-color palettes** (settings → Note colors, `keys3d_bg_palette`, default the per-octave scheme): a per-octave rainbow (each octave its own hue, darker sharps), the original per-pitch "Rainbow" table, vivid/pastel per-pitch variants, and single-hue two-tone palettes (uniform naturals, darker sharps) for players who want "black key coming" to read at a glance; notes, key glow, lane guides and hit flames all follow the pick live.
 - Full RS+ visual treatment: key **letter glyphs** printed on the active-range key tops (cached CanvasTextures), **bevelled gem-style note blocks** (ExtrudeGeometry, geometry/material caches keyed by size and pitch-class×hand), **floating bar numbers** scrolling with the notes, **active-range lane dimming** so the playable span pops, and a **glowing pulsing hit-line** (layered additive gradient planes — no postprocessing).
 - Performance discipline: no per-frame allocations or DOM queries in `draw()`. Chart-scoped resources — note geometries/materials, bar-number and glow textures — are cached and disposed on chart teardown; the key-letter glyph `CanvasTexture`s live in a shared module-level cache that survives teardown and is reused across instances.
 - Auto-selected for arrangements with notation via `matchesArrangement(songInfo.has_notation)`; capability-native `visualization` provider declaration.
 - **Camera settings**: camera-rig presets (`keys3d_bg_camera` — classic low rig / elevated / overhead; default overhead, applied live, adaptive pan-zoom preserved) with base-rig fine-tune sliders for height, distance and tilt (`keys3d_bg_camHeight` / `camDist` / `camTilt`) that nudge the vantage point the follow-motion orbits. Numeric FX keys clamp to per-key declared ranges (`FX_RANGES`, default 0–1).
+- **Highway-layout options** (settings → Highway layout). **Sharps & flats**
+  (`keys3d_bg_sharpMode`, string; default `realistic`) picks the sharp layout:
+  `floating` (original raised-plane sharps, white-only lanes); `flat` (one plane,
+  zero-overlap piano-shaped tiled lanes — white lanes trimmed where a sharp adjoins
+  them, and each sharp leaned toward the edge natural beside it so the naturals come
+  out close to even: C/D/E/F/B equal, G/A a hair smaller since G# can't lean; pure
+  `laneSpanFlat()`); `realistic` (one plane, bars sized like the physical keys — full
+  naturals always rendered full, full black keys drawn on top and only occluding a
+  natural where a sharp note actually coincides in time; pure `laneSpanReal()`).
+  **Lane color opacity** (`keys3d_bg_laneOpacity`, 0–1, default 0) fades the
+  pitch-class lane tint; at 0 (default) the strips are a dark floor with guide lines
+  only at the key-block boundaries (E→F and each octave B→C), so each block is bounded
+  rather than every lane — the notes keep their colors; toward 1 it fills in full,
+  vivid colored lanes. The strips, per-lane separators and block lines crossfade with
+  this value. **Octave separators** (`keys3d_bg_octaveGaps`, default on) widens the
+  gap a touch at each B→C octave boundary. **Octave line contrast**
+  (`keys3d_bg_octaveContrast`, 0–1, default 0.5) scales how hard the B→C octave line
+  reads; it is drawn as a dark layer (scaled by lane opacity) plus a bright layer
+  (scaled by its inverse), so it auto-shifts dark→bright as the lanes fade — no mode
+  switch needed. All are geometry-time — applied on the next chart build via
+  `init()`'s re-read.
 - **Web MIDI input scoring**: module-level MIDI singleton (one access per tab, focused-instance routing) with device auto-connect by saved id+name, loopback blocklist, channel filter, transpose and CC64 sustain (`keys3d_` localStorage prefix; `window.keysH3d*` settings API). Hit detection matches played MIDI against the flattened chart notes within ±0.10 s with per-note dedupe and a missed-note sweep (only while a device is connected — never retroactive across a mid-song connect).
-- **Live hit feedback on the MIDI path** (not the chart): key depress (~4° back-edge pivot, ~120 ms spring; the key letter rides along), wrong-note red key flash, and a vertical flame flare on hits (pooled additive sprites, white-hot base fading into the pitch-class colour, ~400 ms).
+- **Live hit feedback on the MIDI path** (not the chart): key depress (~4° back-edge pivot, ~120 ms spring; the key letter rides along), wrong-note red key flash, and a vertical flame flare on hits (pooled additive sprites, white-hot base fading into the pitch-class color, ~400 ms).
 - **End-of-run stats**: POSTs `/api/stats` `{filename, arrangement, score, accuracy}` exactly once per run with the same formula as the guitar notedetect path (`accuracy = hits / max(1, hits+misses)`, `score = round(hits·100·accuracy)`), then notifies the progression core when present.
 - **Capability wiring** (all guarded for servers without the hosts): registers as a note-detection `midi` provider (`keys-midi`, `verify.target`), opens a per-song binding scoped to the chart's keys range, reports hit/miss observability events, and exposes Web MIDI inputs to the audio-input domain with pseudonymized labels (`midi-input-1`, …) via `source.enumerate/describe/open/close`.
 - Headless test hook: `window.__keysHwTest = { injectNoteOn(midi, when), getScore() }`.

plugins/keys_highway_3d/plugin.json

@@ -1,7 +1,7 @@
 {
   "id": "keys_highway_3d",
   "name": "Keys Highway 3D",
-  "version": "0.1.2",
+  "version": "0.2.1",
   "description": "RS+-style 3D falling-note piano highway fed by the Sloppak Notation Format, with Web MIDI input scoring.",
   "type": "visualization",
   "bundled": true,

plugins/keys_highway_3d/screen.js

@@ -9,7 +9,7 @@
 //
 // Visual contract is the frame analysis on slopsmith#824 (RS+ reference):
 // 3D perspective highway to a vanishing point, notes landing on a real 3D
-// keyboard, per-key Synthesia-style PITCH-CLASS colours (hand is only a
+// keyboard, per-key Synthesia-style PITCH-CLASS colors (hand is only a
 // secondary brightness cue), active-range key highlighting with letters,
 // a glowing hit-line, bevelled cuboid notes sized by durSec, floating bar
 // numbers, and key-depress + flame feedback driven by the LIVE MIDI input
@@ -59,7 +59,7 @@
     // World scroll speed (units / second) — matches the sibling highways.
     const TS = 130 * K;
 
-    // Per-pitch-class colours (Synthesia convention observed in the RS+
+    // Per-pitch-class colors (Synthesia convention observed in the RS+
     // reference frames: C=red, D=yellow, E=blue, F=light blue-grey, …).
     // Index = midi % 12 (C, C#, D, …, B). Sharps take a dimmed blend of
     // their neighbours so black-key notes stay distinguishable.
@@ -79,11 +79,11 @@
     ];
 
     // Hand cue is SECONDARY (slopsmith#824 design call): right hand renders
-    // at full brightness, left hand slightly darkened — colour stays the
+    // at full brightness, left hand slightly darkened — color stays the
     // pitch class.
     const HAND_BRIGHTNESS = { rh: 1.0, lh: 0.72 };
 
-    // Selectable note-colour palettes. Index = midi % 12, same contract as
+    // Selectable note-color palettes. Index = midi % 12, same contract as
     // PITCH_CLASS_COLORS — which stays byte-identical as the 'classic'
     // entry, so anyone who never touches the setting sees the stock look.
     // Two palette families:
@@ -151,7 +151,7 @@
         ],
     };
 
-    // Octave-based colour scheme ('octaves'): every octave gets a distinct
+    // Octave-based color scheme ('octaves'): every octave gets a distinct
     // hue that steps like a rainbow (clear, uniform sections — NOT a smooth
     // blend — so each octave is uniquely identifiable, but neighbouring
     // octaves stay close so the change isn't jarring). Loops if a song runs
@@ -181,7 +181,80 @@
     function _isBlackPc(midi) {
         return [1, 3, 6, 8, 10].indexOf(((midi % 12) + 12) % 12) !== -1;
     }
-    // Colour (24-bit int) for a midi note under the octave scheme: hue by
+    // Which way a sharp leans to even out the naturals: toward the EDGE
+    // natural next to it. +1 = up (toward the higher natural), −1 = down, 0 =
+    // centred. C#/F# sit below an inner natural so they lean down to C/F;
+    // D#/A# lean up to E/B; G# has an inner natural on both sides, so it can't
+    // lean and stays put.
+    function _sharpLeanDir(pc) {
+        if (pc === 1 || pc === 6) return -1;   // C#, F#
+        if (pc === 3 || pc === 10) return 1;   // D#, A#
+        return 0;                              // G#
+    }
+    // Floor span [left,right] of a key's lane in the FLAT (piano-shaped)
+    // layout, in world units, given the key's centre x (`cx`). Pure/isolated
+    // on purpose — this ONE function defines the layout, so a variant is a
+    // one-function swap. Zero-overlap tiling: a white lane is trimmed by
+    // `sharpHalf` wherever it meets a sharp, and the sharp fills that gap. Each
+    // sharp is nudged `shift` toward the edge natural beside it (see
+    // _sharpLeanDir), which steals a sliver from that edge natural and widens
+    // the squeezed inner natural — at shift = sharpHalf/3 the C-D-E-F-B
+    // naturals come out equal. Lanes still tile edge-to-edge (no overlap, no
+    // gap). With `gaps`, each B→C octave boundary opens an extra `octGap`
+    // divider by shaving half of it off the B and the C (naturals only).
+    // `range`, when given, gates the trim to a neighbouring sharp that is
+    // itself inside `range.activeLow..range.activeHigh`. A white key at the
+    // active-range boundary (see the `midi < range.activeLow ||
+    // midi > range.activeHigh` skip around the lane-strip loop) may sit next
+    // to a sharp pitch-class that falls just outside the active range — that
+    // sharp's lane is never drawn, so trimming the white key's edge for it
+    // leaves a dark, unfilled sliver. Gating on range keeps that edge full
+    // while leaving the normal (fully in-range) zero-overlap tiling intact.
+    // Callers that don't pass `range` (e.g. the unit tests exercising raw
+    // tiling geometry) keep the unconditional trim.
+    function laneSpanFlat(midi, black, cx, dims, gaps, range) {
+        const { whiteW, sharpHalf, shift, octGap } = dims;
+        if (black) {
+            const c = cx + _sharpLeanDir(((midi % 12) + 12) % 12) * shift;
+            return { left: c - sharpHalf, right: c + sharpHalf };
+        }
+        const neighborActive = (m) => !range || (m >= range.activeLow && m <= range.activeHigh);
+        // White: each side that meets a sharp is trimmed to that (leaned) sharp's
+        // near edge; a side that meets another white keeps the half-slot edge.
+        let left = cx - whiteW / 2;
+        let right = cx + whiteW / 2;
+        if (_isBlackPc(midi - 1) && neighborActive(midi - 1)) {
+            const bc = (cx - whiteW / 2) + _sharpLeanDir(((midi - 1) % 12 + 12) % 12) * shift;
+            left = bc + sharpHalf;
+        }
+        if (_isBlackPc(midi + 1) && neighborActive(midi + 1)) {
+            const bc = (cx + whiteW / 2) + _sharpLeanDir(((midi + 1) % 12 + 12) % 12) * shift;
+            right = bc - sharpHalf;
+        }
+        const pc = ((midi % 12) + 12) % 12;
+        if (gaps) {
+            if (pc === 11) right -= octGap / 2; // B: gap on its right (→ C)
+            if (pc === 0) left += octGap / 2;   // C: gap on its left (← B)
+        }
+        return { left, right };
+    }
+    // 'realistic' layout span: every bar sized to the physical key it lands on.
+    // Naturals are the same full width (2·natHalf) centred on the key; sharps are
+    // the full black-key width (2·sharpHalf) at their standard half-slot, which
+    // makes them overlap — the caller draws sharps on top. A natural therefore
+    // always renders full and is only covered where a sharp note actually
+    // coincides in time. `gaps` widens the B→C divider (naturals only).
+    function laneSpanReal(midi, black, cx, dims, gaps) {
+        const half = black ? dims.sharpHalf : dims.natHalf;
+        let left = cx - half, right = cx + half;
+        if (gaps && !black) {
+            const pc = ((midi % 12) + 12) % 12;
+            if (pc === 11) right -= dims.octGap / 2;
+            if (pc === 0) left += dims.octGap / 2;
+        }
+        return { left, right };
+    }
+    // Color (24-bit int) for a midi note under the octave scheme: hue by
     // octave, darker for sharps. Pure (no THREE) so it is unit-testable.
     function octaveNoteColor(midi) {
         const oct = Math.floor(midi / 12) - 1;      // C1..B1 => 1
@@ -210,8 +283,8 @@
     // Gem vertical gradient (bottom shade → top highlight), baked per-vertex into
     // the note geometry so a block reads as a lit 3D gem instead of a flat fill —
     // same approach as the bundled guitar highway_3d (`gNoteGrad`). The ramp is
-    // greyscale so one geometry serves every pitch-class colour; the material
-    // multiplies its colour by it via vertexColors.
+    // greyscale so one geometry serves every pitch-class color; the material
+    // multiplies its color by it via vertexColors.
     const GEM_SHADE_BOT = 0.12, GEM_SHADE_TOP = 1.1; // strong gem gradient (top slightly blows toward a highlight)
 
     const NOTE_NAMES = ['C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#', 'A', 'A#', 'B'];
@@ -740,20 +813,36 @@
         _writeStore(STORE_KEYS.midiPick, JSON.stringify({ id: id || '', name: name || '', key: key || '' }));
     }
 
-    function _midiAutoConnect(allowFallback) {
-        // Recovery (sources-changed after unplug) passes false: never switch to a
-        // fallback input, because _midiConnect persists the pick and that would
-        // overwrite the user's saved device on a transient multi-device unplug
-        // (the original returns on replug and reconnects then).
-        if (allowFallback === undefined) allowFallback = true;
-        const inputs = _midiSources();
-        if (!inputs.length) return;
-        const saved = _readSavedPick();
-        // Explicit "None" opt-out.
-        if (saved && saved.id === '' && saved.name === '') return;
-        // Prefer the globally-unique logicalSourceKey, then the legacy bare
-        // sourceId, then case-insensitive name (Chrome on Linux regenerates ids
-        // per page load), then first non-loopback.
+    // Pure decision logic (exported via __test): pick which device to
+    // auto-connect to from the current source list, the domain-wide selection
+    // (`globalKey`, from Settings → Input Setup), and this plugin's own legacy
+    // saved pick. Returns null for "connect to nothing" (explicit None opt-out,
+    // or the configured device currently absent during hotplug recovery).
+    //
+    // The domain-wide selection is the SOURCE OF TRUTH (checked first): a device
+    // configured globally must never be overridden by a stale plugin-local pick
+    // or an arbitrary first-device fallback — that override was the bug. The
+    // local pick is retained only as a fallback BELOW the global (and for
+    // name-recovery when the global's logicalSourceKey went stale, e.g. a
+    // browser that regenerates MIDI port ids across reloads). Auto-connect no
+    // longer writes the local pick, so it only ever holds a value an explicit
+    // selection put there (or a stale one from a pre-fix build — the global
+    // still wins over it).
+    function _pickMidiTarget(inputs, saved, globalKey, allowFallback) {
+        if (!inputs.length) return null;
+        const notBlocked = (i) => !!i && !_MIDI_BLOCKLIST_RE.test(i.name || '');
+        // Explicit "None" opt-out (set only via the device-select API).
+        if (saved && saved.id === '' && saved.name === '') return null;
+
+        // 1. Domain-wide selection (Settings → Input Setup) — source of truth.
+        if (globalKey) {
+            const g = inputs.find(i => i.key === globalKey);
+            if (notBlocked(g)) return g;
+        }
+
+        // 2. Legacy plugin-local pick, as a fallback below the global. Prefer the
+        // globally-unique logicalSourceKey, then the legacy bare sourceId, then
+        // case-insensitive name (Chrome on Linux regenerates ids per page load).
         let target = null;
         if (saved && saved.key) target = inputs.find(i => i.key === saved.key) || null;
         if (!target && saved && saved.id) target = inputs.find(i => i.id === saved.id) || null;
@@ -761,23 +850,50 @@
             const n = saved.name.toLowerCase();
             target = inputs.find(i => (i.name || '').toLowerCase() === n) || null;
         }
-        // Never honour a saved pick that's a loopback / "Midi Through" port — it
-        // carries no device input, so a stale pick silently eats every note. The
-        // saved-pick lookups above bypass the block-list; re-apply it here.
-        if (target && _MIDI_BLOCKLIST_RE.test(target.name || '')) target = null;
-        if (!target) {
-            // Skip the substitute ONLY when a saved pick exists but is currently
-            // absent (recovery: preserve it, don't clobber on a transient unplug).
-            // With no saved pick at all, a fallback is the intended first-hotplug
-            // auto-connect — allow it even in recovery.
-            const hasSavedPick = !!(saved && (saved.key || saved.id || saved.name));
-            if (!allowFallback && hasSavedPick) return;
-            target = inputs.find(i => !_MIDI_BLOCKLIST_RE.test(i.name || '')) || inputs[0];
-        }
+        // Never honour a saved pick that resolves to a loopback / "Midi Through"
+        // port — it carries no device input, so it silently eats every note.
+        if (target && !notBlocked(target)) target = null;
+        if (target) return target;
+
+        // 3. Nothing configured resolved to a present device. In recovery
+        // (allowFallback=false) with a configured preference — a global pick or a
+        // saved pick — that's currently absent, preserve it rather than switching
+        // to an arbitrary device on a transient multi-device unplug. With no
+        // preference at all, a first-device grab is the intended first-hotplug
+        // auto-connect, allowed even in recovery.
+        const hasPreference = !!(globalKey || (saved && (saved.key || saved.id || saved.name)));
+        if (!allowFallback && hasPreference) return null;
+        // Connect to nothing rather than a loopback: if every present device is
+        // blocklisted, a first-device grab would attach to a "Midi Through"/IAC
+        // port that carries no input and silently eats every note.
+        return inputs.find(notBlocked) || null;
+    }
+
+    function _midiAutoConnect(allowFallback) {
+        // Recovery (sources-changed after unplug) passes false: never switch to a
+        // fallback input on a transient multi-device unplug (the configured
+        // device returns on replug and reconnects then). Auto-connect is
+        // non-persisting (persist omitted → false): it opens the resolved device
+        // for this session WITHOUT writing the plugin-local pick or the shared
+        // domain selection, so opening this highway can't clobber the user's
+        // globally-configured device.
+        if (allowFallback === undefined) allowFallback = true;
+        const inputs = _midiSources();
+        const saved = _readSavedPick();
+        const mi = _mi();
+        const globalKey = mi && typeof mi.getSelected === 'function' ? mi.getSelected() : null;
+        const target = _pickMidiTarget(inputs, saved, globalKey, allowFallback);
+        if (!target) return;
         _midiConnect(target.id, target.name, target.key);
     }
 
-    async function _midiConnect(id, name, key) {
+    // `persist` gates the two preference writes. Only an EXPLICIT device
+    // selection (the device-select API) persists: it writes the plugin-local
+    // pick AND the shared domain selection (`mi.select`, so the user's choice
+    // becomes the global default). Auto-connect and programmatic opens pass
+    // falsy — they open the resolved device for this session only, never
+    // touching either store, so they can't clobber a globally-configured device.
+    async function _midiConnect(id, name, key, persist) {
         // Capture our generation AFTER _midiDetach()'s own bump, so a later
         // detach (device removal / new connect / opt-out) reliably supersedes us.
         _midiDetach();
@@ -788,7 +904,7 @@
         for (const inst of _instances) {
             if (inst && typeof inst._releaseAllHeld === 'function') inst._releaseAllHeld();
         }
-        _writeSavedPick(id || '', name || '', key || '');
+        if (persist) _writeSavedPick(id || '', name || '', key || '');
         const mi = _mi();
         if ((id || key) && mi) {
             // Prefer the globally-unique logicalSourceKey so two providers that
@@ -801,13 +917,19 @@
                 const lkey = src.key || ('web-midi::' + src.id);
                 _midiInput = { id: src.id, name: src.name, key: lkey };
                 _midiJustConnected = true;
+                // Only an explicit selection writes the shared global default;
+                // open takes the logicalSourceKey directly, so select() is not
+                // needed to open — it exists purely to set the global. Persist it
+                // BEFORE the no-instance early return so a settings-panel pick with
+                // no live renderer still updates the shared default (best-effort:
+                // a select hiccup must not abort the connect).
+                if (persist) { try { await mi.select(lkey); } catch (_) { /* best-effort */ } }
                 // No live renderer to consume OR release a session — don't hold one
                 // open (settings-only ensure-init, or the last instance was torn
-                // down during async discovery). The pick is saved; a later renderer
-                // mount re-runs auto-connect and opens for real, releasing on destroy.
+                // down during async discovery). A later renderer mount re-runs
+                // auto-connect and opens for real, releasing on destroy.
                 if (_instances.size === 0) { _midiNotifyDeviceListChanged(); return; }
                 try {
-                    await mi.select(lkey);
                     const res = await mi.open({ requester: PLUGIN_ID, logicalSourceKey: lkey });
                     // A newer _midiConnect (device switch / None / replug) ran while
                     // we awaited open — discard this stale session so we don't wire a
@@ -966,10 +1088,11 @@
     window.keysH3dGetMidiInputId = function () { return _midiInput ? _midiInput.id : ''; };
     window.keysH3dSetMidiInput = function (id) {
         // `id` may be a logicalSourceKey (new host calls) or a legacy sourceId.
+        // Explicit user selection → persist (local pick + shared global default).
         const src = id
             ? (_midiSources().find(s => s.key === id) || _midiSources().find(s => s.id === id))
             : null;
-        _midiConnect(src ? src.id : (id || ''), src ? src.name : '', src ? src.key : '');
+        _midiConnect(src ? src.id : (id || ''), src ? src.name : '', src ? src.key : '', true);
         return true;
     };
     window.keysH3dGetMidiChannel = function () { return _cfg.midiChannel; };
@@ -1026,6 +1149,14 @@
         scoreFx: true,    // 2D overlay: +N pops, combo rings, streak-break wash
         bgIntensity: 0.5, // background-ambience density/strength
         bgReactive: true, // background reacts to the audio analyser
+        // Highway-layout options (apply on the next chart build via init()'s
+        // fx re-read). The sharp LAYOUT is a separate string setting
+        // (keys3d_bg_sharpMode); these two are the booleans.
+        octaveGaps: true,      // ON: wider divider gap at each B→C octave boundary
+        laneOpacity: 0.0,      // 0–1: lane-color strength. 0 (default) = dark floor +
+        //                        block guide lines (E→F, B→C); 1 = full colored lanes; crossfades.
+        octaveContrast: 0.5,   // 0–1: how strongly the B→C octave line stands out. It
+        //                        auto-darkens with lane opacity and brightens as it fades.
         // Camera base-rig fine-tune. These shift the BASE vantage point the
         // auto-pan/zoom follow-motion is built on (they multiply/offset the
         // active CAM_PRESET before the per-frame pan + dolly), so the camera
@@ -1223,7 +1354,7 @@
         } catch (_) { /* dispatch unavailable — persisted value applies next init */ }
     };
 
-    // Note-colour palette id — string-valued like the theme, so it gets its
+    // Note-color palette id — string-valued like the theme, so it gets its
     // own validated key + setter rather than an FX_DEFAULTS slot.
     const FX_LS_PALETTE = 'keys3d_bg_palette';
     function readPaletteSetting() {
@@ -1231,7 +1362,7 @@
             const id = localStorage.getItem(FX_LS_PALETTE);
             if (id && PALETTE_IDS.indexOf(id) !== -1) return id;
         } catch (_) {}
-        // Default: the octave scheme (each octave its own colour, darker
+        // Default: the octave scheme (each octave its own color, darker
         // sharps) — the plug-and-play piano look. Emerald/classic/etc. remain
         // selectable.
         return 'octaves';
@@ -1244,6 +1375,30 @@
         } catch (_) { /* dispatch unavailable — persisted value applies next init */ }
     };
 
+    // Sharp-display layout id — string-valued (3-way), its own validated key +
+    // setter. 'floating' = the original raised-plane sharps with white-only
+    // lanes; 'flat' = every note on one plane with piano-shaped tiled lanes
+    // (sharps leaned to even the naturals); 'realistic'
+    // = one plane with note bars sized like the physical keys (full naturals,
+    // full sharps overlapping on top). Geometry-time — applied on the next chart
+    // build via init()'s re-read.
+    const FX_LS_SHARPMODE = 'keys3d_bg_sharpMode';
+    const SHARP_MODES = ['floating', 'flat', 'realistic'];
+    function readSharpModeSetting() {
+        try {
+            const id = localStorage.getItem(FX_LS_SHARPMODE);
+            if (id && SHARP_MODES.indexOf(id) !== -1) return id;
+        } catch (_) {}
+        return 'realistic'; // default layout: physical-key-sized bars on one plane
+    }
+    window.keys3dSetSharpMode = function (id) {
+        if (SHARP_MODES.indexOf(id) === -1) return;
+        try { localStorage.setItem(FX_LS_SHARPMODE, id); } catch (_) {}
+        try {
+            window.dispatchEvent(new CustomEvent('keys3d:settings', { detail: { sharpMode: id } }));
+        } catch (_) { /* dispatch unavailable — persisted value applies next init */ }
+    };
+
     // Camera-rig presets. 'classic' is the original low, near-telephoto rig
     // (numerically identical to the historical constants, so 'classic' with the
     // neutral camTilt default reproduces the exact stock framing). y/z/lookY/lookZ
@@ -1442,6 +1597,8 @@
 
     function _aiOpen(req) {
         // Opening a MIDI source connects the corresponding Web MIDI input.
+        // Programmatic open (audio-input source.open) — non-persisting: it must
+        // not rewrite the user's saved pick or the shared global default.
         const idx = _aiIndexFor(req && (req.sourceId || req.logicalSourceKey));
         const inputs = _midiSources();   // carries .key (logicalSourceKey), unlike _midiListInputs()
         if (idx == null || idx >= inputs.length) {
@@ -1495,6 +1652,41 @@
         _aiRegisteredCount = 0;
     }
 
+    /* ======================================================================
+     *  Camera Director bridge resolver (pure — exported via createFactory.__test)
+     * ====================================================================== */
+
+    /**
+     * The active splitscreen API, defensive on the global-name rename in flight
+     * (feedBackSplitscreen is canonical; slopsmithSplitscreen is the legacy alias).
+     * @returns {object|null} the splitscreen API, or null when not present
+     */
+    function _ssApi() { return window.feedBackSplitscreen || window.slopsmithSplitscreen || null; }
+
+    /**
+     * Resolve the Camera Director camera for a canvas: this panel's camera under
+     * splitscreen, else the global, else null (Camera Director absent → 100% stock
+     * framing). Throw-safe on panelIndexFor so a misbehaving splitscreen build
+     * can't break framing.
+     * @param {HTMLCanvasElement} canvas this renderer's highway canvas
+     * @param {object|null} ss the splitscreen API (see _ssApi)
+     * @param {object|null} panelsMap window.__h3dCamCtlPanels (per-panel cameras by index)
+     * @param {object|null} globalCam window.__h3dCamCtl (single global camera)
+     * @returns {object|null} the resolved free-camera bridge, or null
+     */
+    function _resolveFreeCam(canvas, ss, panelsMap, globalCam) {
+        if (panelsMap && ss && typeof ss.panelIndexFor === 'function') {
+            try {
+                const i = ss.panelIndexFor(canvas);
+                // Only a non-negative integer indexes the panel map — a non-int /
+                // negative / string index (or a prototype key) must not resolve an
+                // unintended/inherited property; fall through to the global then.
+                if (Number.isInteger(i) && i >= 0 && panelsMap[i]) return panelsMap[i];
+            } catch (e) { /* ignore */ }
+        }
+        return globalCam || null;
+    }
+
     /* ======================================================================
      *  Renderer factory
      * ====================================================================== */
@@ -1561,6 +1753,7 @@
         // _applyTheme / _applyCinematic / the glow slider retune them live).
         let _theme = readThemeSetting();
         let _palette = readPaletteSetting();
+        let _sharpMode = readSharpModeSetting(); // 'floating' | 'flat' | 'realistic'
         let ambLight = null, dirLight = null;
         let _floorMat = null;
         const _railMats = [];      // lane-edge rail materials (theme laneDim)
@@ -1628,7 +1821,7 @@
             return (NOTE_PALETTES[_palette] || PITCH_CLASS_COLORS)[pc];
         }
 
-        // Base colour (24-bit int, no hand dimming) for a midi note under the
+        // Base color (24-bit int, no hand dimming) for a midi note under the
         // active palette — the octave scheme is procedural, every other
         // palette is a 12-entry pitch-class table.
         function _noteHex(midi) {
@@ -1664,6 +1857,41 @@
         const WHITE_W = 12 * K, WHITE_L = 46 * K, WHITE_H = 5 * K;
         const BLACK_W = 6.4 * K, BLACK_L = 28 * K, BLACK_H = 6.5 * K;
         const HIGHWAY_LEN = 1150 * K; // longer runway → ~8.8s of lookahead visible
+        // 'flat' piano-shaped-lane geometry (see laneSpanFlat). Zero-overlap tiling:
+        // white lanes are trimmed by FLAT_SHARP_HALF where they meet a sharp and
+        // the sharp fills the gap, so nothing overlaps. To keep the naturals
+        // even, each sharp is nudged FLAT_SHARP_SHIFT toward the EDGE natural
+        // beside it (C#→C, D#→E, F#→F, A#→B; G# stays centred, no edge to lean
+        // on) — that steals a sliver from the edge natural and hands it to the
+        // squeezed inner natural. At shift = sharpHalf/3 the C-D-E-F-B naturals
+        // come out exactly equal; G/A land a hair smaller (G# can't lean). The
+        // sharps ride the same flat plane (no lift — they never overlap a
+        // natural). OCT_GAP is the extra divider opened at each octave boundary
+        // when the octaveGaps option is on.
+        const FLAT_SHARP_HALF = 2.2 * K;                 // sharp half-width (4.4K wide)
+        const FLAT_SHARP_SHIFT = FLAT_SHARP_HALF / 3;    // sharp lean that evens the naturals
+        const OCT_GAP = 0.9 * K;
+        const LANE_DIMS_FLAT = {
+            whiteW: WHITE_W, sharpHalf: FLAT_SHARP_HALF, shift: FLAT_SHARP_SHIFT, octGap: OCT_GAP,
+        };
+        // 'realistic' layout (laneSpanReal): every note bar is the size of the
+        // physical key it lands on — naturals the full white-key width (always
+        // rendered full, only occluded where a sharp note actually overlaps in
+        // time) and sharps the full black-key width at their standard positions,
+        // drawn on top with a hair of REAL_SHARP_LIFT (anti z-fight).
+        const REAL_NAT_HALF = WHITE_W * 0.47;   // natural bar ≈ physical white key (~11.3K)
+        const REAL_SHARP_HALF = BLACK_W / 2;    // sharp bar = physical black key (6.4K)
+        const REAL_SHARP_LIFT = 0.3 * K;
+        const LANE_DIMS_REAL = { natHalf: REAL_NAT_HALF, sharpHalf: REAL_SHARP_HALF, octGap: OCT_GAP };
+        // Lane span for the active non-floating sharp mode. `range`
+        // (activeLow/activeHigh) is optional and only consulted by the flat
+        // layout, to gate the boundary-key edge trim (see laneSpanFlat).
+        const _flatMode = () => _sharpMode === 'flat' || _sharpMode === 'realistic';
+        function laneSpanFor(midi, black, cx, gaps, range) {
+            return _sharpMode === 'realistic'
+                ? laneSpanReal(midi, black, cx, LANE_DIMS_REAL, gaps)
+                : laneSpanFlat(midi, black, cx, LANE_DIMS_FLAT, gaps, range);
+        }
 
         // Camera — the default 'classic' preset is a low, near-telephoto rig
         // (RS+-style): a narrow FOV from low and back gives a deep receding
@@ -1708,7 +1936,19 @@
             _rigOut.lookZ = _camPreset.lookZ;
             return _rigOut;
         }
-        // Per-key approach glow: a key lights in its pitch-class colour ONLY while a
+
+        /**
+         * Camera Director bridge for THIS panel — delegates to the pure, unit-
+         * tested _resolveFreeCam / _ssApi (resolver block above the factory).
+         * Reads the live globals: per-panel map __h3dCamCtlPanels → this panel's
+         * camera, else the global __h3dCamCtl, else null (stock framing).
+         * @param {HTMLCanvasElement} canvas this panel's highway canvas
+         * @returns {object|null} the resolved free-camera bridge, or null
+         */
+        function _freeCamFor(canvas) {
+            return _resolveFreeCam(canvas, _ssApi(), window.__h3dCamCtlPanels, window.__h3dCamCtl);
+        }
+        // Per-key approach glow: a key lights in its pitch-class color ONLY while a
         // note is heading for it, ramping up the closer that note gets to the hit-line.
         const KEY_GLOW_AHEAD = 2.0;      // seconds before the hit-line a key starts to light
         const KEY_GLOW_STRENGTH = 1.15;  // peak emissive intensity (note at the hit-line)
@@ -2297,9 +2537,9 @@
             });
             // Extrusion spans z ∈ [-bevel, depth + bevel]; centre it.
             geo.translate(0, 0, -depth / 2);
-            // Bake a vertical brightness ramp into vertex colours (bottom shade →
+            // Bake a vertical brightness ramp into vertex colors (bottom shade →
             // top highlight) so the gem reads 3D; the material multiplies its
-            // pitch-class colour by this (vertexColors).
+            // pitch-class color by this (vertexColors).
             geo.computeBoundingBox();
             const y0 = geo.boundingBox.min.y, yr = (geo.boundingBox.max.y - y0) || 1;
             const pos = geo.attributes.position;
@@ -2314,10 +2554,10 @@
             return geo;
         }
 
-        // Glossy note material, cached per resolved colour. Keying by the
-        // final colour int (hand brightness already baked in by noteColor)
+        // Glossy note material, cached per resolved color. Keying by the
+        // final color int (hand brightness already baked in by noteColor)
         // works for every palette — including 'octaves', where two notes of
-        // the same pitch class in different octaves are DIFFERENT colours and
+        // the same pitch class in different octaves are DIFFERENT colors and
         // must not share a material (a pitch-class key would collide them).
         function _noteMaterial(midi, hand) {
             const col = noteColor(midi, hand);
@@ -2333,7 +2573,7 @@
             // share one shader program.)
             mat = new T.MeshPhysicalMaterial({
                 color: col,
-                vertexColors: true,         // multiply colour by the baked gem ramp
+                vertexColors: true,         // multiply color by the baked gem ramp
                 emissive: col,
                 emissiveIntensity: NOTE_EMISSIVE_BASE * _glowMul(),
                 roughness: 0.32,
@@ -2355,7 +2595,10 @@
             return 0.72 + 0.22 * Math.min(1, Math.max(0, fx.vibrancy));
         }
         function _laneGuideOpacity() {
-            return 0.10 + 0.12 * Math.min(1, Math.max(0, fx.vibrancy));
+            // Vibrancy sets the ceiling (much brighter than the old subtle
+            // 0.10–0.22 range); the laneOpacity slider then scales 0 → ceiling.
+            const vib = 0.32 + 0.52 * Math.min(1, Math.max(0, fx.vibrancy)); // ~0.32..0.84
+            return vib * Math.min(1, Math.max(0, fx.laneOpacity));
         }
 
         // Live vibrancy slider: retint everything already built — the
@@ -2371,13 +2614,13 @@
             for (const m of _laneGuideMats) m.opacity = lop;
         }
 
-        // Live palette switch: recolour everything already built — cached
+        // Live palette switch: recolor everything already built — cached
         // note materials (future clones), per-note clones, key emissives
         // (incl. the wrong-flash restore state), lane guides — and drop the
         // pitch-class flame textures so the next spawn bakes the new hues.
         // Same no-rebuild approach as _applyVibrancy.
         function _applyPalette() {
-            // The base-material cache is keyed by resolved colour, so old
+            // The base-material cache is keyed by resolved color, so old
             // entries are simply stale under a new palette — drop them and let
             // the next build re-cache. The live per-note clones below are
             // retinted directly from each note's midi (palette-correct).
@@ -2441,10 +2684,10 @@
         }
 
         // Vertical flame texture for hit flares / held-key halos: white-hot
-        // base fading up into the note's colour, with a horizontal falloff.
-        // Cached per resolved colour (bounded — 12 for pitch-class palettes,
+        // base fading up into the note's color, with a horizontal falloff.
+        // Cached per resolved color (bounded — 12 for pitch-class palettes,
         // up to ~one-per-octave for 'octaves'), so a flare always matches the
-        // struck note's colour whatever the palette.
+        // struck note's color whatever the palette.
         function _flameTexture(midi) {
             const c = _noteHex(midi);
             let tex = _flameTexCache.get(c);
@@ -2624,9 +2867,9 @@
                 }
             }
 
-            // Lane guides: a faint colour strip running up the runway from each
-            // active key, in that key's pitch-class colour. A falling note shares
-            // its target key's colour, so the player can trace it straight down
+            // Lane guides: a faint color strip running up the runway from each
+            // active key, in that key's pitch-class color. A falling note shares
+            // its target key's color, so the player can trace it straight down
             // its lane to the right key even when it sits near the frame edge.
             //
             // The lanes sit at the NOTES' travel height (coplanar), not on the
@@ -2636,29 +2879,87 @@
             // lane, perfectly aligned with the lane and its key.
             const guideLen = HIGHWAY_LEN - WHITE_L;
             const laneY = WHITE_H + NOTE_H / 2 + 0.5 * K; // == white-note travel height
+            const gaps = fx.octaveGaps;
+            const floating = _sharpMode === 'floating';
+            const t = Math.min(1, Math.max(0, fx.laneOpacity));       // lane-color opacity
+            const octC = Math.min(1, Math.max(0, fx.octaveContrast)); // 0..1 line-contrast
+            const themeLaneDim = (() => { const c = _bgThemeColors(_theme); return c.laneDim != null ? c.laneDim : 0x2a2a3e; })();
+            // A vertical guide line running the full runway at world x (skips
+            // near-transparent lines so the crossfade never builds dead meshes).
+            const addLine = (x, color, opacity, wpx, trackTheme) => {
+                if (opacity < 0.02) return;
+                const m = new T.MeshBasicMaterial({ color, transparent: true, opacity, depthWrite: false });
+                if (trackTheme) _railMats.push(m); // theme retint tracks these; fixed guides stay put
+                const line = new T.Mesh(new T.PlaneGeometry(wpx, guideLen), m);
+                line.rotation.x = -Math.PI / 2;
+                line.position.set(x, laneY + 0.06 * K, hitZ - guideLen / 2);
+                keyboardGroup.add(line);
+            };
             for (const [midi, entry] of layout) {
                 if (midi < range.activeLow || midi > range.activeHigh) continue;
-                if (entry.black) continue; // one strip per semitone-slot lands on whites
-                const gmat = new T.MeshBasicMaterial({
-                    color: noteColor(midi, 'rh'), transparent: true,
-                    opacity: _laneGuideOpacity(), depthWrite: false,
-                });
-                gmat.userData.midi = midi; // palette retint needs the lane's pitch
-                _laneGuideMats.push(gmat);
-                const strip = new T.Mesh(new T.PlaneGeometry(WHITE_W * 0.84, guideLen), gmat);
-                strip.rotation.x = -Math.PI / 2;
-                strip.position.set(keyX(entry, whiteCount), laneY, hitZ - guideLen / 2);
-                keyboardGroup.add(strip);
-                // Thin brighter rails at the lane edges for crisp separation.
-                const railMat = new T.MeshBasicMaterial({
-                    color: (() => { const c = _bgThemeColors(_theme); return c.laneDim != null ? c.laneDim : 0x2a2a3e; })(),
-                    transparent: true, opacity: 0.5, depthWrite: false,
-                });
-                _railMats.push(railMat);
-                const rail = new T.Mesh(new T.PlaneGeometry(0.6 * K, guideLen), railMat);
-                rail.rotation.x = -Math.PI / 2;
-                rail.position.set(keyX(entry, whiteCount) - WHITE_W / 2, laneY + 0.05 * K, hitZ - guideLen / 2);
-                keyboardGroup.add(rail);
+                // Floating: white-only lanes (blacks float, lane-less). Flat/
+                // realistic: every key gets a piano-shaped lane.
+                if (entry.black && floating) continue;
+                // Lane footprint per mode.
+                let left, right, stripY = laneY;
+                if (floating) {
+                    const cx = keyX(entry, whiteCount);
+                    left = cx - WHITE_W / 2; right = cx + WHITE_W / 2;
+                    if (gaps) {
+                        const pc = ((midi % 12) + 12) % 12;
+                        if (pc === 11) right -= OCT_GAP / 2; // B → C boundary
+                        if (pc === 0) left += OCT_GAP / 2;
+                    }
+                } else {
+                    const span = laneSpanFor(midi, entry.black, keyX(entry, whiteCount), gaps, range);
+                    left = span.left; right = span.right;
+                    if (_sharpMode === 'realistic' && entry.black) stripY = laneY + REAL_SHARP_LIFT;
+                }
+                const center = (left + right) / 2;
+                // Colored lane strip + a subtle per-lane separator — fade in with
+                // lane opacity. (As lanes fade, the block/octave lines below take
+                // over as the guide.)
+                if (t > 0.02) {
+                    // Floating keeps the historical 0.84-wide white strip; the
+                    // piano-shaped lanes inset a touch for a dark separator.
+                    const stripW = floating ? (right - left) - WHITE_W * 0.16 : (right - left) * 0.9;
+                    const gmat = new T.MeshBasicMaterial({
+                        color: noteColor(midi, 'rh'), transparent: true,
+                        opacity: _laneGuideOpacity(), depthWrite: false, // includes lane opacity
+                    });
+                    gmat.userData.midi = midi; // palette retint needs the lane's pitch
+                    _laneGuideMats.push(gmat);
+                    const strip = new T.Mesh(new T.PlaneGeometry(stripW, guideLen), gmat);
+                    strip.rotation.x = -Math.PI / 2;
+                    strip.position.set(center, stripY, hitZ - guideLen / 2);
+                    keyboardGroup.add(strip);
+                    // Per-lane separator, fading with the strips. Skip realistic
+                    // sharps (they overlap the white columns).
+                    if (!(entry.black && _sharpMode === 'realistic')) {
+                        addLine(left, themeLaneDim, 0.5 * t, 0.6 * K, true);
+                    }
+                }
+            }
+            // Structural divider lines: ONE per "block" boundary — E→F and B→C —
+            // so each block of keys (C-D-E, F-G-A-B) is bounded, not every lane.
+            // They crossfade IN as the lanes fade OUT. The B→C octave line is a
+            // dark layer (reads over bright lanes, scales with lane opacity) plus
+            // a bright layer (reads over the dark floor, scales with the inverse),
+            // so it auto-shifts dark→bright as you fade lanes; octaveContrast
+            // scales the whole thing.
+            for (let midi = range.activeLow; midi <= range.activeHigh; midi++) {
+                const pc = ((midi % 12) + 12) % 12;
+                const isEF = pc === 4;   // E → F block boundary
+                const isBC = pc === 11;  // B → C octave boundary
+                if (!isEF && !isBC) continue;
+                const boundaryX = keyX(layout.get(midi), whiteCount) + WHITE_W / 2;
+                if (isBC) {
+                    addLine(boundaryX, 0x05060a, octC * 0.92 * t, 1.1 * K, false);              // dark, over lanes
+                    addLine(boundaryX, 0xd8dcec, (0.42 + octC * 0.5) * (1 - t), 1.1 * K, false); // bright, over floor
+                } else {
+                    // E→F block divider — a guide that appears as the lanes fade.
+                    addLine(boundaryX, 0x6a6a7a, 0.5 * (1 - t), 0.8 * K, false);
+                }
             }
 
             // Keys (whites first so blacks overlay). Geometries are shared
@@ -2678,7 +2979,7 @@
                 const inRange = midi >= range.activeLow && midi <= range.activeHigh;
                 const material = new T.MeshStandardMaterial({
                     color: black ? 0x070708 : 0xe8e8ee,
-                    // Pitch-class colour preset on emissive but OFF at rest — the key
+                    // Pitch-class color preset on emissive but OFF at rest — the key
                     // is neutral until a note approaches, when updateScene ramps the
                     // intensity up by proximity.
                     emissive: noteColor(midi, 'rh'),
@@ -2764,11 +3065,31 @@
                 const entry = layout.get(note.midi);
                 if (!entry) continue;
                 const len = Math.max(4 * K, note.durSec * TS);
-                const w = (entry.black ? BLACK_W : WHITE_W * 0.94) * 0.9;
+                // Non-floating layouts: notes ride the naturals' plane and take
+                // their piano-shaped lane's width/centre. Floating (default):
+                // original elevated sharps, key-centred bars.
+                let w, x, y;
+                if (_flatMode()) {
+                    const span = laneSpanFor(
+                        note.midi, entry.black, keyX(entry, whiteCount), fx.octaveGaps, range);
+                    // 'realistic' bars are full (physical-key size); 'flat' bars are
+                    // inset a touch for a dark separator in the tight tiling.
+                    const inset = _sharpMode === 'realistic' ? 1.0 : 0.9;
+                    w = (span.right - span.left) * inset;
+                    x = (span.left + span.right) / 2;
+                    // Coplanar; in 'realistic' the sharps ride a hair proud so they
+                    // draw over the naturals they overlap without z-fighting.
+                    const lift = (_sharpMode === 'realistic' && entry.black) ? REAL_SHARP_LIFT : 0;
+                    y = WHITE_H + NOTE_H / 2 + 0.5 * K + lift;
+                } else {
+                    w = (entry.black ? BLACK_W : WHITE_W * 0.94) * 0.9;
+                    x = keyX(entry, whiteCount);
+                    y = (entry.black ? BLACK_H + WHITE_H : WHITE_H) + NOTE_H / 2 + 0.5 * K;
+                }
                 // Clone per note so each can glow independently while being consumed.
                 const mesh = new T.Mesh(_noteGeometry(w, len), _noteMaterial(note.midi, note.hand).clone());
-                mesh.position.x = keyX(entry, whiteCount);
-                mesh.position.y = (entry.black ? BLACK_H + WHITE_H : WHITE_H) + NOTE_H / 2 + 0.5 * K;
+                mesh.position.x = x;
+                mesh.position.y = y;
                 mesh.visible = false;
                 notesGroup.add(mesh);
                 // Note-name label: a camera-facing sprite (readable at this low camera
@@ -3037,7 +3358,33 @@
             }
             _camX += (_camTargetX - _camX) * CAM_PAN_LERP;
             _camZoom += (_camTargetZoom - _camZoom) * CAM_ZOOM_LERP;
-            { const r = _rig(); cam.position.set(_camX, r.y * K * _camZoom, r.z * K * _camZoom); cam.lookAt(_camX, r.lookY * K * _camZoom, r.lookZ * K * _camZoom); }
+            {
+                const r = _rig();
+                let _cx = _camX, _cy = r.y * K * _camZoom, _cz = r.z * K * _camZoom;
+                let _lx = _camX, _ly = r.lookY * K * _camZoom, _lz = r.lookZ * K * _camZoom;
+                // Camera Director free-cam offsets (per-panel-aware), layered on top
+                // of the auto-framing so pan/zoom-follow still works. Dolly/height/
+                // orbit act on the camera-from-target vector; pan/pitch shift the
+                // look target. NaN-safe; null/disabled bridge → stock.
+                const _fc = _freeCamFor(highwayCanvas);
+                if (_fc && _fc.enabled) {
+                    const _dm = Number.isFinite(_fc.distMul) ? _fc.distMul : 1;
+                    const _hm = Number.isFinite(_fc.heightMul) ? _fc.heightMul : 1;
+                    const _yaw = Number.isFinite(_fc.yaw) ? _fc.yaw : 0;
+                    let _vx = _cx - _lx, _vy = _cy - _ly, _vz = _cz - _lz;
+                    _vx *= _dm; _vy *= _dm; _vz *= _dm;   // dolly (zoom)
+                    _vy *= _hm;                            // height
+                    const _cyw = Math.cos(_yaw), _syw = Math.sin(_yaw);
+                    const _rx = _vx * _cyw - _vz * _syw, _rz = _vx * _syw + _vz * _cyw; // orbit around Y
+                    _cx = _lx + _rx; _cy = _ly + _vy; _cz = _lz + _rz;
+                    const _px = Number.isFinite(_fc.panX) ? _fc.panX : 0;
+                    const _py = Number.isFinite(_fc.panY) ? _fc.panY : 0;
+                    const _pt = Number.isFinite(_fc.pitch) ? _fc.pitch : 0;
+                    _lx += _px * K; _ly += (_pt + _py) * K;
+                }
+                cam.position.set(_cx, _cy, _cz);
+                cam.lookAt(_lx, _ly, _lz);
+            }
 
             for (const km of keyMeshes.values()) km.userData.glow = 0;
             for (const { mesh, note, len, label } of noteMeshes) {
@@ -3483,6 +3830,7 @@
                 // listening (e.g. changed on the Settings screen, where the live
                 // viz is torn down) must not come up stale on a later init().
                 _palette = readPaletteSetting();
+                _sharpMode = readSharpModeSetting();
                 _camPreset = CAM_PRESETS[readCameraSetting()] || CAM_PRESETS.classic;
                 _theme = readThemeSetting();
                 _bgStyle = readBgStyleSetting();
@@ -3533,6 +3881,10 @@
                             _palette = d.palette;
                             _applyPalette();
                         }
+                        if (d && d.sharpMode && SHARP_MODES.indexOf(d.sharpMode) !== -1) {
+                            // Geometry-time — takes effect on the next chart build.
+                            _sharpMode = d.sharpMode;
+                        }
                         if (d && d.camera && CAM_PRESETS[d.camera]) {
                             _camPreset = CAM_PRESETS[d.camera];
                             // Position/lookAt re-derive next frame; only the
@@ -3733,6 +4085,8 @@
     };
     // Pure data-layer + scoring hooks for headless tests.
     window.slopsmithViz_keys_highway_3d.__test = {
+        _resolveFreeCam,
+        _ssApi,
         beatDurSec,
         flattenNotation,
         keyRange,
@@ -3749,6 +4103,8 @@
         readBgStyleSetting,
         readPaletteSetting,
         readCameraSetting,
+        readSharpModeSetting,
+        SHARP_MODES,
         _bgThemeColors,
         BG_THEMES,
         BG_STYLE_IDS,
@@ -3757,10 +4113,14 @@
         PALETTE_IDS,
         OCTAVE_HUES,
         octaveNoteColor,
+        _isBlackPc,
+        laneSpanFlat,
+        laneSpanReal,
         CAM_PRESETS,
         FX_DEFAULTS,
         FX_RANGES,
         _classifyTiming,
+        _pickMidiTarget,
     };
 
     // Headless verification hook: lets Playwright drive synthetic note-ons

plugins/keys_highway_3d/settings.html

@@ -12,11 +12,11 @@
     <div class="mt-3">
         <h4 class="text-xs font-medium text-gray-300 mb-2">Graphics</h4>
 
-        <label for="keysh3d-fx-palette" class="text-xs font-medium text-gray-400 mb-1 block">Note colours</label>
+        <label for="keysh3d-fx-palette" class="text-xs font-medium text-gray-400 mb-1 block">Note colors</label>
         <select id="keysh3d-fx-palette"
             onchange="window.keys3dSetPalette && window.keys3dSetPalette(this.value)"
             class="w-full bg-dark-700 border border-gray-800 rounded-lg px-3 py-2 text-xs text-gray-300 outline-none">
-            <option value="octaves" selected>Octaves (colour per octave, darker sharps)</option>
+            <option value="octaves" selected>Octaves (color per octave, darker sharps)</option>
             <option value="emerald">Emerald (green, darker sharps)</option>
             <option value="ice">Ice (blue, darker sharps)</option>
             <option value="classic">Rainbow (per-pitch)</option>
@@ -24,7 +24,7 @@
             <option value="pastel">Pastel (per-pitch, soft)</option>
         </select>
         <p class="text-xs text-gray-500 mt-1 mb-3">
-            Choose the colour scheme for the falling notes, key glow, lane
+            Choose the color scheme for the falling notes, key glow, lane
             guides and hit flames. Each option is described in its own label.
         </p>
 
@@ -46,8 +46,8 @@
         </select>
         <p class="text-xs text-gray-500 mt-1 mb-3">
             Background gradient, floor and lane rails — the same theme names
-            as the guitar highway. Note colours come from the
-            "Note colours" palette above.
+            as the guitar highway. Note colors come from the
+            "Note colors" palette above.
         </p>
 
         <label for="keysh3d-fx-camera" class="text-xs font-medium text-gray-400 mb-1 block">Camera angle</label>
@@ -101,6 +101,64 @@
             aims higher up the runway or down toward the keys. 0 = neutral.
         </p>
 
+        <h4 class="text-xs font-medium text-gray-300 mb-2 mt-4">Highway layout</h4>
+
+        <label for="keysh3d-fx-sharpmode" class="text-xs font-medium text-gray-400 mb-1 block">Sharps &amp; flats</label>
+        <select id="keysh3d-fx-sharpmode"
+            onchange="window.keys3dSetSharpMode && window.keys3dSetSharpMode(this.value)"
+            class="w-full bg-dark-700 border border-gray-800 rounded-lg px-3 py-2 text-xs text-gray-300 outline-none">
+            <option value="floating">Floating</option>
+            <option value="flat">Non-floating</option>
+            <option value="realistic" selected>Realistic key sizes (default — best with no colored lanes)</option>
+        </select>
+        <p class="text-xs text-gray-500 mt-1 mb-3">
+            How sharps and flats are drawn. <em>Floating</em>: they ride a raised
+            plane above the naturals. <em>Non-floating</em>: everything on one
+            plane, each key its own even piano-shaped lane. <em>Realistic key
+            sizes</em>: one plane, bars sized like the real keys (full naturals,
+            full black keys on top). Applies next time you open a song.
+        </p>
+
+        <label for="keysh3d-fx-laneopacity" class="text-xs font-medium text-gray-400 mb-1 block">
+            Lane color opacity <span id="keysh3d-fx-laneopacity-val" class="text-gray-500 font-mono">0.00</span>
+        </label>
+        <input type="range" id="keysh3d-fx-laneopacity"
+            min="0" max="1" step="0.05" value="0"
+            oninput="window.keys3dSetFx && window.keys3dSetFx('laneOpacity', this.value); document.getElementById('keysh3d-fx-laneopacity-val').textContent = parseFloat(this.value).toFixed(2)"
+            class="w-full">
+        <p class="text-xs text-gray-500 mt-1 mb-3">
+            How strongly each lane is tinted its note color. 0.00 (default) is a
+            dark floor with plain guide lines only between the key blocks (at E–F
+            and each octave); the notes keep their colors and pop off the floor.
+            Raise toward 1.00 for full, vivid colored lanes. Applies next time you
+            open a song.
+        </p>
+
+        <label for="keysh3d-fx-octavegaps" class="flex items-center gap-2 text-xs text-gray-300 cursor-pointer mt-3">
+            <input type="checkbox" id="keysh3d-fx-octavegaps" checked
+                onchange="window.keys3dSetFx && window.keys3dSetFx('octaveGaps', this.checked)">
+            Octave separators
+        </label>
+        <p class="text-xs text-gray-500 mt-1 mb-3">
+            Widen the gap a little at each octave boundary (every B to the C
+            above it) so octaves are easier to read. Applies next time you open
+            a song.
+        </p>
+
+        <label for="keysh3d-fx-octavecontrast" class="text-xs font-medium text-gray-400 mb-1 mt-3 block">
+            Octave line contrast <span id="keysh3d-fx-octavecontrast-val" class="text-gray-500 font-mono">0.50</span>
+        </label>
+        <input type="range" id="keysh3d-fx-octavecontrast"
+            min="0" max="1" step="0.05" value="0.5"
+            oninput="window.keys3dSetFx && window.keys3dSetFx('octaveContrast', this.value); document.getElementById('keysh3d-fx-octavecontrast-val').textContent = parseFloat(this.value).toFixed(2)"
+            class="w-full">
+        <p class="text-xs text-gray-500 mt-1 mb-3">
+            How strongly the octave line (every B to C) stands out. It adapts to
+            the lane color opacity automatically — darkening the line against
+            bright lanes and brightening it as you fade them toward the dark
+            floor. Applies next time you open a song.
+        </p>
+
         <label for="keysh3d-fx-cinematic" class="flex items-center gap-2 text-xs text-gray-300 cursor-pointer">
             <input type="checkbox" id="keysh3d-fx-cinematic" checked
                 onchange="window.keys3dSetFx && window.keys3dSetFx('cinematic', this.checked)">
@@ -184,7 +242,7 @@
         <label for="keysh3d-fx-timing" class="flex items-center gap-2 text-xs text-gray-300 cursor-pointer mt-3">
             <input type="checkbox" id="keysh3d-fx-timing" checked
                 onchange="window.keys3dSetFx && window.keys3dSetFx('timingFx', this.checked)">
-            Timing colours
+            Timing colors
         </label>
         <p class="text-xs text-gray-500 mt-1">
             Tint the sparks by timing — on-time green, early cyan, late
@@ -247,6 +305,9 @@
             hydrateFxBool('cinematic', 'keysh3d-fx-cinematic');
             hydrateFxBool('bgReactive', 'keysh3d-fx-bgreactive');
             hydrateFxBool('scoreFx', 'keysh3d-fx-scorefx');
+            // Highway-layout: octaveGaps defaults ON (bool); laneOpacity /
+            // octaveContrast are 0-1 sliders hydrated with hydrateFxRange below.
+            hydrateFxBool('octaveGaps', 'keysh3d-fx-octavegaps');
             const hydrateFxRange = (key, elId, valId) => {
                 const n = parseFloat(localStorage.getItem('keys3d_bg_' + key));
                 if (!Number.isFinite(n)) return;
@@ -258,6 +319,8 @@
             hydrateFxRange('vibrancy', 'keysh3d-fx-vibrancy', 'keysh3d-fx-vibrancy-val');
             hydrateFxRange('glow', 'keysh3d-fx-glow', 'keysh3d-fx-glow-val');
             hydrateFxRange('bgIntensity', 'keysh3d-fx-bgintensity', 'keysh3d-fx-bgintensity-val');
+            hydrateFxRange('laneOpacity', 'keysh3d-fx-laneopacity', 'keysh3d-fx-laneopacity-val');
+            hydrateFxRange('octaveContrast', 'keysh3d-fx-octavecontrast', 'keysh3d-fx-octavecontrast-val');
             // Camera fine-tune sliders live outside 0-1 — clamp to the
             // control's own min/max (mirrors screen.js FX_RANGES).
             const hydrateFxRangeIn = (key, elId, valId) => {
@@ -291,6 +354,11 @@
             if (storedPalette && Array.from(paletteSel.options).some(o => o.value === storedPalette)) {
                 paletteSel.value = storedPalette;
             }
+            const storedSharp = localStorage.getItem('keys3d_bg_sharpMode');
+            const sharpSel = document.getElementById('keysh3d-fx-sharpmode');
+            if (storedSharp && Array.from(sharpSel.options).some(o => o.value === storedSharp)) {
+                sharpSel.value = storedSharp;
+            }
         } catch (e) {
             console.warn('[Keys-Hwy3D settings] hydration failed:', e);
         }

plugins/keys_highway_3d/tests/camera_bridge.test.js

@@ -0,0 +1,78 @@
+// Camera Director bridge resolver tests: per-panel select, global fallback,
+// null-when-absent, throw-safety, and the splitscreen global-name alias. Loads
+// screen.js in a bare vm window and exercises the __test exports (no DOM/WebGL).
+const { test } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+const vm = require('node:vm');
+
+function load() {
+    const window = {
+        console,
+        location: { protocol: 'http:', host: 'localhost' },
+        slopsmith: {},
+    };
+    window.window = window;
+    window.globalThis = window;
+    const context = vm.createContext(window);
+    const src = fs.readFileSync(path.join(__dirname, '..', 'screen.js'), 'utf8');
+    vm.runInContext(src, context, { filename: 'screen.js' });
+    return { window, __test: window.slopsmithViz_keys_highway_3d.__test };
+}
+
+test('_resolveFreeCam: per-panel camera under splitscreen', () => {
+    const { __test } = load();
+    const c0 = {}, c1 = {};
+    const ss = { panelIndexFor: (c) => (c === c0 ? 0 : 1) };
+    const map = { 0: { id: 'p0' }, 1: { id: 'p1' } };
+    assert.equal(__test._resolveFreeCam(c0, ss, map, { id: 'g' }).id, 'p0');
+    assert.equal(__test._resolveFreeCam(c1, ss, map, { id: 'g' }).id, 'p1');
+});
+
+test('_resolveFreeCam: falls back to global when there is no panel map', () => {
+    const { __test } = load();
+    const g = { id: 'global' };
+    assert.equal(__test._resolveFreeCam({}, { panelIndexFor: () => 0 }, null, g), g);
+});
+
+test('_resolveFreeCam: falls back to global when the panel has no map entry', () => {
+    const { __test } = load();
+    const g = { id: 'global' };
+    const ss = { panelIndexFor: () => 3 };            // index 3 absent from map
+    assert.equal(__test._resolveFreeCam({}, ss, { 0: {} }, g), g);
+});
+
+test('_resolveFreeCam: null when Camera Director is absent (no global)', () => {
+    const { __test } = load();
+    assert.equal(__test._resolveFreeCam({}, null, null, null), null);
+    assert.equal(__test._resolveFreeCam({}, { panelIndexFor: () => 0 }, {}, undefined), null);
+});
+
+test('_resolveFreeCam: throw-safe on panelIndexFor → falls back to global', () => {
+    const { __test } = load();
+    const g = { id: 'global' };
+    const ss = { panelIndexFor: () => { throw new Error('boom'); } };
+    assert.equal(__test._resolveFreeCam({}, ss, { 0: {} }, g), g);
+});
+
+test('_resolveFreeCam: NaN/negative/float/string index → falls back to global', () => {
+    const { __test } = load();
+    const g = { id: 'global' };
+    assert.equal(__test._resolveFreeCam({}, { panelIndexFor: () => NaN }, { 0: {} }, g), g);
+    assert.equal(__test._resolveFreeCam({}, { panelIndexFor: () => -1 }, { 0: {} }, g), g);
+    assert.equal(__test._resolveFreeCam({}, { panelIndexFor: () => 0.5 }, { 0: {} }, g), g);
+    // A string/prototype key must not resolve an inherited property (e.g. toString).
+    assert.equal(__test._resolveFreeCam({}, { panelIndexFor: () => 'toString' }, {}, g), g);
+});
+
+test('_ssApi: null when neither global set; slopsmith alias; feedBack canonical wins', () => {
+    const { window, __test } = load();
+    assert.equal(__test._ssApi(), null);
+    const legacy = { panelIndexFor: () => 0 };
+    window.slopsmithSplitscreen = legacy;
+    assert.equal(__test._ssApi(), legacy);            // legacy alias picked up
+    const current = { panelIndexFor: () => 1 };
+    window.feedBackSplitscreen = current;
+    assert.equal(__test._ssApi(), current);           // canonical name takes precedence
+});

plugins/keys_highway_3d/tests/data_layer.test.js

@@ -188,3 +188,99 @@ test('measureMarkers extracts idx/t pairs', () => {
         [{ idx: 1, t: 0 }, { idx: 2, t: 2.5 }],
     );
 });
+
+test('_pickMidiTarget: no plugin-local pick defers to the domain-wide selection, not "first device"', () => {
+    const { _pickMidiTarget } = load();
+    const inputs = [
+        { id: 'a', name: 'Device A', key: 'web-midi::a' },
+        { id: 'b', name: 'Device B', key: 'web-midi::b' },
+    ];
+    // Fresh install / never picked here — must use the Input Setup global,
+    // NOT fall through to inputs[0].
+    const target = _pickMidiTarget(inputs, null, 'web-midi::b', true);
+    assert.equal(target.id, 'b');
+});
+
+test('_pickMidiTarget: the domain-wide selection is the source of truth — it wins over a stale plugin-local pick', () => {
+    const { _pickMidiTarget } = load();
+    const inputs = [
+        { id: 'a', name: 'Device A', key: 'web-midi::a' },
+        { id: 'b', name: 'Device B', key: 'web-midi::b' },
+    ];
+    // A stale local pick (e.g. left by a pre-fix build's auto-connect) must
+    // NOT override the device the user configured in Settings → Input Setup.
+    const target = _pickMidiTarget(inputs, { id: 'a', name: 'Device A', key: 'web-midi::a' }, 'web-midi::b', true);
+    assert.equal(target.id, 'b');
+});
+
+test('_pickMidiTarget: local pick is used as a fallback when no global is configured', () => {
+    const { _pickMidiTarget } = load();
+    const inputs = [
+        { id: 'a', name: 'Device A', key: 'web-midi::a' },
+        { id: 'b', name: 'Device B', key: 'web-midi::b' },
+    ];
+    const target = _pickMidiTarget(inputs, { id: 'a', name: 'Device A', key: 'web-midi::a' }, null, true);
+    assert.equal(target.id, 'a');
+});
+
+test('_pickMidiTarget: local pick name-recovers when its logicalSourceKey went stale (id regeneration)', () => {
+    const { _pickMidiTarget } = load();
+    // Same physical device, new id/key across a reload; the saved key/id miss
+    // but the name still matches.
+    const inputs = [{ id: 'a2', name: 'Device A', key: 'web-midi::a2' }];
+    const target = _pickMidiTarget(inputs, { id: 'a1', name: 'Device A', key: 'web-midi::a1' }, null, true);
+    assert.equal(target.id, 'a2');
+});
+
+test('_pickMidiTarget: domain-wide selection is ignored if it names a blocklisted loopback port', () => {
+    const { _pickMidiTarget } = load();
+    const inputs = [
+        { id: 'thru', name: 'IAC Driver Bus 1', key: 'web-midi::thru' },
+        { id: 'b', name: 'Device B', key: 'web-midi::b' },
+    ];
+    const target = _pickMidiTarget(inputs, null, 'web-midi::thru', true);
+    assert.equal(target.id, 'b'); // falls through to the first non-loopback device
+});
+
+test('_pickMidiTarget: when every present device is a loopback, connect to nothing (never a dead port)', () => {
+    const { _pickMidiTarget } = load();
+    const inputs = [
+        { id: 'thru', name: 'MIDI Through Port-0', key: 'web-midi::thru' },
+        { id: 'iac', name: 'IAC Driver Bus 1', key: 'web-midi::iac' },
+    ];
+    // No non-loopback device exists — must NOT fall back to inputs[0] (a port
+    // that carries no input and would silently eat every note).
+    const target = _pickMidiTarget(inputs, null, null, true);
+    assert.equal(target, null);
+});
+
+test('_pickMidiTarget: explicit "None" opt-out still wins over any global default', () => {
+    const { _pickMidiTarget } = load();
+    const inputs = [{ id: 'a', name: 'Device A', key: 'web-midi::a' }];
+    const target = _pickMidiTarget(inputs, { id: '', name: '' }, 'web-midi::a', true);
+    assert.equal(target, null);
+});
+
+test('_pickMidiTarget: a present global wins even during hotplug recovery', () => {
+    const { _pickMidiTarget } = load();
+    const inputs = [{ id: 'b', name: 'Device B', key: 'web-midi::b' }];
+    // The configured global device is present — reconnect to it, don't bail.
+    const target = _pickMidiTarget(inputs, null, 'web-midi::b', false);
+    assert.equal(target.id, 'b');
+});
+
+test('_pickMidiTarget: recovery (allowFallback=false) preserves an absent configured device instead of grabbing a random one', () => {
+    const { _pickMidiTarget } = load();
+    const inputs = [{ id: 'b', name: 'Device B', key: 'web-midi::b' }];
+    // The configured device ('x', global) is currently unplugged; a transient
+    // recovery must NOT switch to the unrelated device that is present.
+    const target = _pickMidiTarget(inputs, null, 'web-midi::x', false);
+    assert.equal(target, null);
+});
+
+test('_pickMidiTarget: recovery with no preference at all still allows a first-hotplug grab', () => {
+    const { _pickMidiTarget } = load();
+    const inputs = [{ id: 'b', name: 'Device B', key: 'web-midi::b' }];
+    const target = _pickMidiTarget(inputs, null, null, false);
+    assert.equal(target.id, 'b');
+});

plugins/keys_highway_3d/tests/fx_settings.test.js

@@ -397,3 +397,156 @@ test('keys3dSetCamera: persists + dispatches valid ids, ignores unknown', () =>
     assert.equal(readCameraSetting(), 'overhead');
 });
 
+/* ── Flat-sharps / piano-shaped lanes (feat/keys3d-flat-lanes) ───────── */
+
+test('FX defaults: octave separators on, lanes off (minimal default look)', () => {
+    const { FX_DEFAULTS } = load().slopsmithViz_keys_highway_3d.__test;
+    assert.equal(FX_DEFAULTS.octaveGaps, true);   // octave separators ship on
+    assert.equal(FX_DEFAULTS.laneOpacity, 0.0);   // dark floor + guide lines by default
+    assert.equal(FX_DEFAULTS.octaveContrast, 0.5);
+    // Sharp LAYOUT is a string setting, not an FX bool.
+    assert.equal('flatSharps' in FX_DEFAULTS, false);
+    assert.equal('laneColors' in FX_DEFAULTS, false); // superseded by laneOpacity
+});
+
+test('keys3dSetFx: highway-layout controls persist (bool + sliders)', () => {
+    const store = {};
+    const win = load({
+        localStorage: {
+            getItem: (k) => (k in store ? store[k] : null),
+            setItem: (k, v) => { store[k] = v; },
+        },
+        dispatchEvent: () => true,
+        CustomEvent: class { constructor(t, o) { this.type = t; this.detail = o && o.detail; } },
+    });
+    win.keys3dSetFx('octaveGaps', true);
+    assert.equal(store.keys3d_bg_octaveGaps, '1');
+    // laneOpacity / octaveContrast are 0-1 numbers, persisted verbatim + clamped.
+    win.keys3dSetFx('laneOpacity', 0.35);
+    assert.equal(store.keys3d_bg_laneOpacity, '0.35');
+    win.keys3dSetFx('laneOpacity', 5); // clamps to the 0-1 range
+    assert.equal(store.keys3d_bg_laneOpacity, '1');
+    win.keys3dSetFx('octaveContrast', 0.8);
+    assert.equal(store.keys3d_bg_octaveContrast, '0.8');
+});
+
+test('sharpMode: realistic default, validated ids, persists + dispatches', () => {
+    const bare = load().slopsmithViz_keys_highway_3d.__test;
+    assert.deepEqual([...bare.SHARP_MODES], ['floating', 'flat', 'realistic']);
+    assert.equal(bare.readSharpModeSetting(), 'realistic'); // no localStorage → default
+    const store = {};
+    const events = [];
+    const win = load({
+        localStorage: {
+            getItem: (k) => (k in store ? store[k] : null),
+            setItem: (k, v) => { store[k] = v; },
+        },
+        dispatchEvent: (ev) => { events.push(ev); return true; },
+        CustomEvent: class { constructor(t, o) { this.type = t; this.detail = o && o.detail; } },
+    });
+    win.keys3dSetSharpMode('flat'); // a non-default id, to exercise persistence
+    assert.equal(store.keys3d_bg_sharpMode, 'flat');
+    assert.equal(events[0].detail.sharpMode, 'flat');
+    assert.equal(win.slopsmithViz_keys_highway_3d.__test.readSharpModeSetting(), 'flat');
+    // Unknown id ignored (no write, no event).
+    win.keys3dSetSharpMode('bogus');
+    assert.equal(store.keys3d_bg_sharpMode, 'flat');
+    assert.equal(events.length, 1);
+});
+
+test('laneSpanFlat (V5): lanes tile with zero overlap and even the naturals', () => {
+    const { laneSpanFlat, _isBlackPc } = load().slopsmithViz_keys_highway_3d.__test;
+    const sh = 2.2, shift = 2.2 / 3;
+    const dims = { whiteW: 12, sharpHalf: sh, shift, octGap: 0.9 }; // mirrors shipped LANE_DIMS_FLAT
+    // cx for one octave: whites on integer slots, blacks on half-slots — the
+    // same slot geometry keyLayout/keyX produce (cx = slot * whiteW=12).
+    const CX = {
+        60: 0, 61: 6, 62: 12, 63: 18, 64: 24, 65: 36, 66: 42,
+        67: 48, 68: 54, 69: 60, 70: 66, 71: 72, 72: 84,
+    };
+    const midis = [60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72];
+    const spans = midis.map((m) => laneSpanFlat(m, _isBlackPc(m), CX[m], dims, false));
+    const wOf = (s) => s.right - s.left;
+    const w = (m) => wOf(spans[midis.indexOf(m)]);
+    // Zero-overlap tiling: every lane abuts the previous one (no gap, no overlap).
+    for (let i = 1; i < spans.length; i++) {
+        assert.ok(Math.abs(spans[i].left - spans[i - 1].right) < 1e-9, 'lane ' + midis[i] + ' abuts');
+    }
+    // Sharps are all the same width.
+    for (const m of [61, 63, 66, 68, 70]) {
+        assert.ok(Math.abs(w(m) - 2 * sh) < 1e-9, 'sharp ' + m + ' width');
+    }
+    // The lean evens the naturals: C, D, E, F, B all come out equal.
+    for (const m of [62, 64, 65, 71]) {
+        assert.ok(Math.abs(w(m) - w(60)) < 1e-9, 'natural ' + m + ' == C (evened)');
+    }
+    // G and A are the only slightly-smaller naturals (G# can't lean) — still
+    // clearly wider than a sharp, and MUCH closer to the rest than plain V2
+    // (which would leave D at 12−2·sh, far below C's 12−sh).
+    assert.ok(Math.abs(w(67) - w(69)) < 1e-9, 'G == A');
+    assert.ok(w(67) < w(60) && w(67) > 2 * sh, 'G/A a touch smaller, still wider than a sharp');
+    assert.ok(w(60) - w(67) < sh, 'natural spread is under one sharp-width');
+});
+
+test('laneSpanReal (V4): naturals uniform, sharps full-width and overlapping', () => {
+    const { laneSpanReal } = load().slopsmithViz_keys_highway_3d.__test;
+    const dims = { natHalf: 5.64, sharpHalf: 3.2, octGap: 0.9 }; // mirrors LANE_DIMS_REAL
+    const wOf = (s) => s.right - s.left;
+    // Every natural is the same full width, whatever its neighbours.
+    for (const [midi, slot] of [[60, 0], [62, 1], [64, 2], [67, 4], [71, 6]]) {
+        assert.ok(Math.abs(wOf(laneSpanReal(midi, false, slot * 12, dims, false)) - 2 * 5.64) < 1e-9,
+            'natural ' + midi + ' uniform');
+    }
+    // Sharps are the full (wider) black-key width and overlap their naturals.
+    const C = laneSpanReal(60, false, 0, dims, false);
+    const Cs = laneSpanReal(61, true, 6, dims, false);
+    assert.ok(Math.abs(wOf(Cs) - 2 * 3.2) < 1e-9, 'sharp full width');
+    assert.ok(Cs.left < C.right, 'sharp overlaps (tucks over) the natural');
+});
+
+test('laneSpanFlat (V5): octaveGaps widens B→C by octGap, sharps unaffected', () => {
+    const { laneSpanFlat } = load().slopsmithViz_keys_highway_3d.__test;
+    const dims = { whiteW: 12, sharpHalf: 2.2, shift: 2.2 / 3, octGap: 0.9 };
+    const gapOff = laneSpanFlat(72, false, 84, dims, false).left - laneSpanFlat(71, false, 72, dims, false).right;
+    const gapOn = laneSpanFlat(72, false, 84, dims, true).left - laneSpanFlat(71, false, 72, dims, true).right;
+    assert.ok(Math.abs((gapOn - gapOff) - dims.octGap) < 1e-9, 'B→C divider grows by octGap');
+    // Sharps are unaffected by the octave-gap option.
+    const s = laneSpanFlat(61, true, 6, dims, true);
+    assert.ok(Math.abs((s.right - s.left) - 2 * dims.sharpHalf) < 1e-9, 'sharp width unchanged by gaps');
+});
+
+test('laneSpanFlat (V5): active-range boundary key is NOT trimmed by an out-of-range neighbor sharp', () => {
+    const { laneSpanFlat } = load().slopsmithViz_keys_highway_3d.__test;
+    const dims = { whiteW: 12, sharpHalf: 2.2, shift: 2.2 / 3, octGap: 0.9 }; // mirrors LANE_DIMS_FLAT
+    // F (midi 65, cx 36): its upper neighbor F# (66) is a sharp. When F sits
+    // at range.activeHigh and F# is excluded from the active range, F# never
+    // gets a lane drawn (see the activeLow/activeHigh skip around the
+    // lane-strip loop) — trimming F's right edge for it would leave a dark,
+    // unfilled sliver. The edge should stay full instead.
+    const highBoundary = { activeLow: 60, activeHigh: 65 };
+    const fAtBoundary = laneSpanFlat(65, false, 36, dims, false, highBoundary);
+    assert.ok(Math.abs(fAtBoundary.right - (36 + dims.whiteW / 2)) < 1e-9,
+        'F right edge stays full when F# is out of the active range');
+    // Same key, but now F# IS in the active range: normal zero-overlap
+    // tiling applies — the trim matches the ungated (no-range) call exactly,
+    // so in-range geometry is unaffected by this fix.
+    const highIncluded = { activeLow: 60, activeHigh: 66 };
+    const fWithSharpInRange = laneSpanFlat(65, false, 36, dims, false, highIncluded);
+    const fUngated = laneSpanFlat(65, false, 36, dims, false);
+    assert.ok(Math.abs(fWithSharpInRange.right - fUngated.right) < 1e-9,
+        'F trims normally once F# is back in range');
+    assert.ok(fWithSharpInRange.right < fAtBoundary.right, 'in-range trim is narrower than the boundary full edge');
+
+    // Symmetric case on the low edge: D (midi 62, cx 12), lower neighbor C#
+    // (61) excluded when D sits at range.activeLow.
+    const lowBoundary = { activeLow: 62, activeHigh: 72 };
+    const dAtBoundary = laneSpanFlat(62, false, 12, dims, false, lowBoundary);
+    assert.ok(Math.abs(dAtBoundary.left - (12 - dims.whiteW / 2)) < 1e-9,
+        'D left edge stays full when C# is out of the active range');
+    const lowIncluded = { activeLow: 61, activeHigh: 72 };
+    const dWithSharpInRange = laneSpanFlat(62, false, 12, dims, false, lowIncluded);
+    const dUngated = laneSpanFlat(62, false, 12, dims, false);
+    assert.ok(Math.abs(dWithSharpInRange.left - dUngated.left) < 1e-9,
+        'D trims normally once C# is back in range');
+});
+

scripts/perf-baseline.mjs

@@ -0,0 +1,177 @@
+// Perf-baseline harness for the module-migration refactor (R0).
+//
+// Rerun this after every phase (R0 → R3c) to prove the split does not regress
+// screen-entry, frame-time, memory, or server latency. It writes a markdown
+// results block to stdout; paste it into docs/perf-baseline.md (or redirect).
+//
+// Usage:
+//   node scripts/perf-baseline.mjs --base http://127.0.0.1:8000 [--n 60] [--soak 30]
+//   node scripts/perf-baseline.mjs --base http://127.0.0.1:8300 --song "Arcturus ….feedpak"
+//
+// With --song, it additionally measures the 2D highway's PER-FRAME DRAW cost:
+// it wraps requestAnimationFrame before any page script runs, tags the frames
+// in which the highway actually painted (via highway.addDrawHook), starts
+// playback, and reports draw-frame p50/p95/p99 over --frames seconds. Tagging
+// matters — roughly half the rAF callbacks belong to other cheap loops, and
+// averaging them in hides a renderer regression behind ~0.1 ms no-op frames.
+// This is the metric that gates the highway.js split (R3c); run it before AND
+// after each highway change on the same machine.
+//
+// Maintainer/CI-only dev tooling (uses the committed @playwright/test browser);
+// never part of the serve or Docker path. Metrics that need a seeded library
+// with charts (playback frame-time, screen-entry into a live highway) are
+// clearly labelled — run those against an environment with real songs.
+
+import { createRequire } from 'module';
+const require = createRequire(import.meta.url);
+const { chromium } = require('@playwright/test');
+
+const args = new Map();
+for (let i = 2; i < process.argv.length; i += 2) args.set(process.argv[i].replace(/^--/, ''), process.argv[i + 1]);
+const BASE = args.get('base') || 'http://127.0.0.1:8000';
+const N = parseInt(args.get('n') || '60', 10);
+const SOAK_S = parseInt(args.get('soak') || '30', 10);
+const SONG = args.get('song') || null;
+const FRAME_S = parseInt(args.get('frames') || '10', 10);
+const RUNS = parseInt(args.get('runs') || '3', 10);   // repeat frame sampling to show spread
+
+const pct = (xs, p) => {
+    if (!xs.length) return null;
+    const s = [...xs].sort((a, b) => a - b);
+    return s[Math.min(s.length - 1, Math.floor((p / 100) * s.length))];
+};
+const ms = (x) => (x == null ? '—' : `${x.toFixed(1)}`);
+
+// ── Server latency: p50/p95/p99 over N requests per endpoint ──────────────────
+async function serverLatency(paths) {
+    const rows = [];
+    for (const path of paths) {
+        const t = [];
+        let status = 0;
+        for (let i = 0; i < N; i++) {
+            const t0 = performance.now();
+            try {
+                const r = await fetch(BASE + path);
+                status = r.status;
+                await r.arrayBuffer();
+            } catch { status = -1; }
+            t.push(performance.now() - t0);
+        }
+        rows.push({ path, status, p50: pct(t, 50), p95: pct(t, 95), p99: pct(t, 99) });
+    }
+    return rows;
+}
+
+// ── Client: cold boot-to-interactive + idle memory after a soak ───────────────
+async function clientMetrics() {
+    const browser = await chromium.launch();
+    const page = await browser.newPage();
+    const t0 = Date.now();
+    await page.goto(BASE, { waitUntil: 'networkidle', timeout: 60000 });
+    const bootMs = Date.now() - t0;
+
+    // performance.memory is Chromium-only; JS heap after settle.
+    const mem0 = await page.evaluate(() => (performance.memory ? performance.memory.usedJSHeapSize : null));
+    await page.waitForTimeout(SOAK_S * 1000);
+    const mem1 = await page.evaluate(() => (performance.memory ? performance.memory.usedJSHeapSize : null));
+
+    const scripts = await page.evaluate(() =>
+        document.querySelectorAll('script[data-plugin-id]').length);
+
+    await browser.close();
+    return { bootMs, memStartMB: mem0 && mem0 / 1048576, memSoakMB: mem1 && mem1 / 1048576, scripts };
+}
+
+// ── 2D highway per-frame draw cost (needs --song + a seeded library) ──────────
+async function frameTimeOnce(browser) {
+    const page = await browser.newPage();
+    let f, t2, notes;
+    try {
+        // Wrap rAF before any page script; mark frames the highway actually drew.
+        await page.addInitScript(() => {
+            window.__f = [];
+            window.__drew = false;
+            const raf = window.requestAnimationFrame.bind(window);
+            window.requestAnimationFrame = (cb) => raf((t) => {
+                window.__drew = false;
+                const t0 = performance.now();
+                try { cb(t); } finally { window.__f.push({ ms: performance.now() - t0, drew: window.__drew }); }
+            });
+        });
+        await page.goto(BASE, { waitUntil: 'networkidle', timeout: 60000 });
+        await page.evaluate(() => document.getElementById('v3-onboarding')?.remove());
+        await page.evaluate((s) => window.playSong(s), SONG);
+        await page.waitForFunction(() => (window.highway?.getNotes?.() || []).length >= 0 && window.highway?.getSongInfo?.(),
+            null, { timeout: 45000 }).catch(() => {});
+        await page.waitForFunction(() => (window.highway?.getNotes?.() || []).length > 0, null, { timeout: 45000 });
+        await page.evaluate(() => window.highway.addDrawHook(() => { window.__drew = true; }));
+        // Start playback so draw() leaves its paused-throttle path; confirm the clock advances.
+        await page.evaluate(async () => { const a = window.highway.getAudioElement?.(); if (a) a.muted = true; await a?.play?.(); });
+        await page.waitForTimeout(1500);
+        const t1 = await page.evaluate(() => window.highway.getTime());
+        await page.evaluate(() => { window.__f.length = 0; });
+        await page.waitForTimeout(FRAME_S * 1000);
+        ({ f, t2, notes } = await page.evaluate(() => ({
+            f: window.__f.slice(), t2: window.highway.getTime(), notes: window.highway.getNotes().length,
+        })));
+        if (!(t2 > t1 + 1)) throw new Error(`clock did not advance (${t1}→${t2}) — measured the paused path`);
+    } finally {
+        // Always close, even when an await above throws — otherwise a failing
+        // run leaks its page until the final browser.close().
+        await page.close();
+    }
+    const drew = f.filter((x) => x.drew).map((x) => x.ms);
+    return { drew, total: f.length, notes };
+}
+
+async function frameTime() {
+    const browser = await chromium.launch({ args: ['--autoplay-policy=no-user-gesture-required'] });
+    const rows = [];
+    for (let i = 0; i < RUNS; i++) {
+        try {
+            const r = await frameTimeOnce(browser);
+            rows.push({
+                p50: pct(r.drew, 50), p95: pct(r.drew, 95), p99: pct(r.drew, 99),
+                max: Math.max(...r.drew), n: r.drew.length, total: r.total, notes: r.notes,
+            });
+        } catch (e) { rows.push({ error: String(e.message || e) }); }
+    }
+    await browser.close();
+    return rows;
+}
+
+const server = await serverLatency([
+    '/api/version',
+    '/api/plugins',
+    '/api/library?limit=60',
+    '/api/library/artists',
+]);
+const client = await clientMetrics();
+
+const now = new Date().toISOString();
+let out = `\n<!-- generated by scripts/perf-baseline.mjs @ ${now} against ${BASE} (n=${N}, soak=${SOAK_S}s) -->\n\n`;
+out += `### Server latency (ms)\n\n| Endpoint | status | p50 | p95 | p99 |\n|---|---|---|---|---|\n`;
+for (const r of server) out += `| \`${r.path}\` | ${r.status} | ${ms(r.p50)} | ${ms(r.p95)} | ${ms(r.p99)} |\n`;
+out += `\n### Client\n\n| Metric | Value |\n|---|---|\n`;
+out += `| Cold boot → networkidle | ${client.bootMs} ms |\n`;
+out += `| JS heap after load | ${client.memStartMB ? client.memStartMB.toFixed(1) + ' MB' : '—'} |\n`;
+out += `| JS heap after ${SOAK_S}s idle soak | ${client.memSoakMB ? client.memSoakMB.toFixed(1) + ' MB' : '—'} |\n`;
+out += `| Plugin scripts injected | ${client.scripts} |\n`;
+if (SONG) {
+    const frames = await frameTime();
+    out += `\n### 2D highway per-frame draw cost — \`${SONG}\` (${RUNS} runs × ${FRAME_S}s)\n\n`;
+    out += `| run | draw frames | p50 | p95 | p99 | max |\n|---|---|---|---|---|---|\n`;
+    for (let i = 0; i < frames.length; i++) {
+        const r = frames[i];
+        if (r.error) { out += `| ${i + 1} | — | \`${r.error}\` | | | |\n`; continue; }
+        out += `| ${i + 1} | ${r.n}/${r.total} | ${ms(r.p50)} | ${ms(r.p95)} | ${ms(r.p99)} | ${ms(r.max)} |\n`;
+    }
+    const p95s = frames.filter((r) => !r.error).map((r) => r.p95);
+    if (p95s.length) out += `\n**p95 spread across runs: ${ms(Math.min(...p95s))}–${ms(Math.max(...p95s))} ms**\n`;
+} else {
+    out += `\n> **Requires a seeded library** (not captured by this run): playback frame-time p95\n`;
+    out += `> on the 2D highway — pass \`--song "<filename in DLC_DIR>"\` to capture it.\n`;
+    out += `> (3D highway_3d + screen-entry timings are a separate R4 concern.)\n`;
+}
+
+console.log(out);

static/app.js

@@ -1110,6 +1110,7 @@ const _LIB_VIEW_VALUES = new Set(['grid', 'tree', 'folder']);
 const _LIB_SORT_VALUES = new Set([
     'artist', 'artist-desc', 'title', 'title-desc',
     'recent', 'year-desc', 'year', 'tuning',
+    'difficulty', 'difficulty-desc',
 ]);
 const _LIB_FORMAT_VALUES = new Set(['', 'sloppak', 'loose']);
 // Tree-view expand/collapse persistence. Three states per tree:
@@ -2078,6 +2079,7 @@ function renderGridCards(songs, containerId = 'lib-grid', mode = 'replace') {
                     ${(() => { const _nm = _getArrangementNamingMode(); return (song.arrangements || []).map(a => _arrangementBadgeHtml(a, _nm)).join(''); })()}
                     ${tuning ? `<span class="px-1.5 py-0.5 rounded ${tuning === 'E Standard' ? 'bg-green-900/30 text-green-400' : 'bg-yellow-900/30 text-yellow-400'}">${esc(tuning)}</span>` : ''}
                     ${song.has_lyrics ? `<span class="px-1.5 py-0.5 bg-purple-900/30 rounded text-purple-300">Lyrics</span>` : ''}
+                    ${song.user_difficulty != null ? `<span class="px-1.5 py-0.5 bg-blue-900/30 rounded text-blue-300" title="Your difficulty rating">◆${esc(song.user_difficulty)}</span>` : ''}
                     ${duration ? `<span class="text-gray-600">${duration}</span>` : ''}
                 </div>
                 ${retuneBtn}
@@ -2277,6 +2279,8 @@ async function renderTreeInto(containerId, countId, stats, letter, q, favoritesO
                     html += `<span class="px-1.5 py-0.5 rounded ${tuning === 'E Standard' ? 'bg-green-900/30 text-green-400' : 'bg-yellow-900/30 text-yellow-400'}">${esc(tuning)}</span>`;
                 if (song.has_lyrics)
                     html += `<span class="px-1.5 py-0.5 bg-purple-900/30 rounded text-purple-300">Lyrics</span>`;
+                if (song.user_difficulty != null)
+                    html += `<span class="px-1.5 py-0.5 bg-blue-900/30 rounded text-blue-300" title="Your difficulty rating">◆${esc(song.user_difficulty)}</span>`;
                 if (duration)
                     html += `<span class="text-gray-600 w-10 text-right">${duration}</span>`;
                 if (stdRetune)
@@ -4860,6 +4864,47 @@ window.jucePlayer = jucePlayer;
     // (a network blip on /api/audio-local-path, an isAudioRunning() race
     // during a device restart) are deliberately NOT memoised so they retry.
     let _rerouteRejectedUrl = null;
+    // Exclusive-style output backends silence every other client on the
+    // endpoint — including our own <audio> element. The share mode IS the
+    // JUCE output device type: "Windows Audio (Exclusive Mode)" is a
+    // hardcoded, unlocalised JUCE type name; ASIO drivers typically hold
+    // the endpoint exclusively too. "Windows Audio (Low Latency Mode)" is
+    // shared and must NOT match.
+    function _isExclusiveOutputType(t) {
+        return t === 'Windows Audio (Exclusive Mode)' || t === 'ASIO';
+    }
+    // [feedpak-route] diagnostics: log the raw outputType string once per
+    // value change (this runs on a 350ms poll — logging every tick would
+    // flood the diagnostics buffer).
+    let _loggedOutputType;
+    async function _outputIsExclusive() {
+        if (typeof juceApi.getCurrentDevice !== 'function') {
+            if (_loggedOutputType !== '<no-getCurrentDevice>') {
+                _loggedOutputType = '<no-getCurrentDevice>';
+                console.warn('[feedpak-route] juceApi.getCurrentDevice missing — cannot detect exclusive output');
+            }
+            return false;
+        }
+        try {
+            const dev = await juceApi.getCurrentDevice();
+            const t = dev?.outputType || dev?.type || '';
+            const excl = _isExclusiveOutputType(t);
+            if (t !== _loggedOutputType) {
+                _loggedOutputType = t;
+                console.log('[feedpak-route] outputType=', JSON.stringify(t), '→ exclusive=', excl);
+            }
+            return excl;
+        } catch (e) {
+            if (_loggedOutputType !== '<getCurrentDevice-failed>') {
+                _loggedOutputType = '<getCurrentDevice-failed>';
+                console.warn('[feedpak-route] getCurrentDevice failed:', e);
+            }
+            return false;
+        }
+    }
+    // highway.js's initial song-load routing consults this for the same
+    // feedpak-under-exclusive decision the watcher makes below.
+    window._juceOutputIsExclusive = _outputIsExclusive;
     // Returns true when window._currentSongAudio no longer references the exact
     // snapshot object captured at reroute entry — i.e. the song was swapped (or
     // cleared) mid-flight. Staleness is detected by object-reference identity,
@@ -4900,8 +4945,12 @@ window.jucePlayer = jucePlayer;
         audio.pause();
         try {
             const res = await fetch(`/api/audio-local-path?url=${encodeURIComponent(url)}`);
-            if (!res.ok) throw new Error('HTTP ' + res.status);
+            if (!res.ok) {
+                console.warn('[feedpak-route] audio-local-path HTTP', res.status, 'for', url);
+                throw new Error('HTTP ' + res.status);
+            }
             const { path } = await res.json();
+            console.log('[feedpak-route] audio-local-path resolved:', (typeof path === 'string' && path.split(/[\\/]/).pop()) || '<missing>');
             if (_isStale(songAudio)) return 'stale';   // song changed mid-fetch
             const ok = await juceApi.loadBackingTrack(path);
             if (ok === false) {
@@ -5119,8 +5168,12 @@ window.jucePlayer = jucePlayer;
     async function _reevaluateJuceRouting() {
         if (_rerouteInFlight) return;
         const songAudio = window._currentSongAudio;
-        // Only /audio/ songs are JUCE-routable; sloppak stems stay on HTML5.
-        if (!songAudio || !songAudio.juceEligible) return;
+        // /audio/ songs are always JUCE-routable. A feedpak full-mix
+        // (single-mix pack, no stems) is routable ONLY under an
+        // exclusive-style output — in shared mode it must stay on HTML5 so
+        // the stem mixer / WebAudio path keeps working. Sloppak stem URLs
+        // are never routable (per-stem mix can't ride a single transport).
+        if (!songAudio || (!songAudio.juceEligible && !songAudio.feedpakFullMix)) return;
         // Don't race highway.js's own initial song-load routing: it owns
         // _juceMode until _juceRoutingPromise settles. Re-running our switch
         // concurrently would double-call loadBackingTrack for the same URL.
@@ -5138,13 +5191,30 @@ window.jucePlayer = jucePlayer;
             try { running = await juceApi.isAudioRunning(); }
             catch (_) { return; }
             if (_isStale(songAudio)) return;               // song changed during IPC
-            if (!!running === !!window._juceMode) return;  // routing already consistent
-
-            const wantJuce = running && !window._juceMode;
+            // Eligibility is evaluated per tick, not snapshotted at song load:
+            // the output share mode can change mid-song (device switch in the
+            // Audio Engine panel), and a feedpak full-mix must follow it —
+            // exclusive → ride the engine; back to shared → return to HTML5.
+            let eligible = !!songAudio.juceEligible;
+            if (!eligible && songAudio.feedpakFullMix && running) {
+                eligible = await _outputIsExclusive();
+                if (_isStale(songAudio)) return;           // song changed during IPC
+            }
+            const wantJuce = !!(running && eligible);
+            // [feedpak-route] diagnostics: one line per decision change (the
+            // watcher polls at 350ms; steady state must not spam the buffer).
+            const _decision = 'running=' + running + ' eligible=' + eligible
+                + ' feedpakFullMix=' + !!songAudio.feedpakFullMix
+                + ' juceMode=' + !!window._juceMode + ' url=' + songAudio.url;
+            if (_decision !== window._lastFeedpakRouteDecision) {
+                window._lastFeedpakRouteDecision = _decision;
+                console.log('[feedpak-route] watcher:', _decision);
+            }
+            if (wantJuce === !!window._juceMode) return;   // routing already consistent
             // Don't keep retrying a track JUCE explicitly rejected.
             if (wantJuce && songAudio.url === _rerouteRejectedUrl) return;
 
-            if (running) {
+            if (wantJuce) {
                 const outcome = await _switchHtml5ToJuce(songAudio);
                 // Memoise ONLY an explicit hard JUCE reject. A successful
                 // switch clears the memo; a 'stale' abort (song changed
@@ -5159,9 +5229,10 @@ window.jucePlayer = jucePlayer;
                 // outcome === 'stale': leave _rerouteRejectedUrl as-is.
             } else {
                 await _switchJuceToHtml5(songAudio);
-                // The engine just stopped. Clear any hard-reject memo so a
-                // later engine restart re-evaluates the track at least once —
-                // the rejection may have been a transient device/decoder state.
+                // The engine stopped (or a feedpak's output left exclusive
+                // mode). Clear any hard-reject memo so a later engine restart
+                // or mode change re-evaluates the track at least once — the
+                // rejection may have been a transient device/decoder state.
                 _rerouteRejectedUrl = null;
             }
         } catch (e) {
@@ -5193,6 +5264,209 @@ window.jucePlayer = jucePlayer;
     }, 350);
 })();
 
+// Renderer-audio bus feeder (desktop Phase 2): when the engine holds the
+// output endpoint in an exclusive-style mode, Chromium cannot reach the
+// device, so any song audio still played by the renderer goes silent. The
+// Phase 1 watcher above already migrates what a single-file transport can
+// carry (loose /audio/ songs, feedpak full-mixes) onto the native backing
+// transport. This feeder covers the rest — the stems plugin's multi-stem
+// WebAudio graph, plus <audio>-element songs the native transport could not
+// take (e.g. a codec loadBackingTrack rejected).
+//
+// Mechanism: capture the renderer-side master with an AudioWorklet tap,
+// re-point the owning AudioContext at a null sink so it keeps rendering
+// without a device, and push ~10 ms chunks over IPC into the engine's
+// renderer bus, where they are mixed into the exclusive output like a
+// backing track (~10-20 ms added latency on song audio only; the guitar
+// monitoring path is untouched). Validated by the fix12 tester spike:
+// null-sink rendering works, clocks hold (drift → 0), no overflow.
+//
+// Docker sphere: window.feedBackDesktop is undefined → this whole block is
+// inert. Shared-mode desktop: the bus stays disabled (no double audio) and
+// captured contexts keep/regain their default sink.
+(function _installRendererBusFeeder() {
+    const api = window.feedBackDesktop?.audio;
+    if (!api || typeof api.setRendererBus !== 'function'
+             || typeof api.pushRendererAudio !== 'function') return;
+
+    const TAP_WORKLET = `
+        class FeedbackBusTap extends AudioWorkletProcessor {
+            process(inputs) {
+                const inp = inputs[0];
+                if (inp && inp[0]) {
+                    const L = inp[0], R = inp[1] || inp[0];
+                    const out = new Float32Array(L.length * 2);
+                    for (let i = 0; i < L.length; i++) { out[i*2] = L[i]; out[i*2+1] = R[i]; }
+                    this.port.postMessage(out, [out.buffer]);
+                }
+                return true;
+            }
+        }
+        registerProcessor('feedback-bus-tap', FeedbackBusTap);
+    `;
+    const _tapModuleUrl = URL.createObjectURL(new Blob([TAP_WORKLET], { type: 'application/javascript' }));
+    const _tapModuleLoaded = new WeakSet();   // AudioContexts with the module added
+
+    // One tap per captured graph. `active` gates the push (the worklet keeps
+    // running when inactive — it's silent bookkeeping, not audio).
+    function _makeTap(ctx) {
+        const state = { node: null, active: false, batch: [], batchFrames: 0 };
+        state.attach = async (sourceNode) => {
+            if (!_tapModuleLoaded.has(ctx)) {
+                await ctx.audioWorklet.addModule(_tapModuleUrl);
+                _tapModuleLoaded.add(ctx);
+            }
+            if (!state.node) {
+                state.node = new AudioWorkletNode(ctx, 'feedback-bus-tap', { numberOfInputs: 1, channelCount: 2 });
+                const BATCH = Math.round(ctx.sampleRate / 100);   // ~10 ms
+                state.node.port.onmessage = (e) => {
+                    if (!state.active) { state.batch = []; state.batchFrames = 0; return; }
+                    state.batch.push(e.data);
+                    state.batchFrames += e.data.length / 2;
+                    if (state.batchFrames >= BATCH) {
+                        const merged = new Float32Array(state.batchFrames * 2);
+                        let o = 0;
+                        for (const c of state.batch) { merged.set(c, o); o += c.length; }
+                        api.pushRendererAudio(merged, ctx.sampleRate);
+                        state.batch = []; state.batchFrames = 0;
+                    }
+                };
+            }
+            sourceNode.connect(state.node);
+            // No onward connection: the tap is a sink-side observer; audibility
+            // in shared mode comes from the graph's own destination path.
+        };
+        state.detach = (sourceNode) => {
+            state.active = false;
+            state.batch = []; state.batchFrames = 0;
+            if (state.node && sourceNode) {
+                try { sourceNode.disconnect(state.node); } catch (_) { /* already gone */ }
+            }
+        };
+        return state;
+    }
+
+    // ── Core <audio> element capture ─────────────────────────────────────────
+    // createMediaElementSource permanently reroutes the element into its
+    // context, so it is created lazily — only the first time an exclusive
+    // device actually needs it — and never torn down. From then on the element
+    // always plays through _elCtx; sink toggling routes it to the speakers
+    // (shared mode) or the null sink + bus (exclusive mode).
+    let _elCtx = null, _elSource = null, _elTap = null;
+    async function _ensureElementCapture() {
+        if (_elCtx) return;
+        const el = document.getElementById('audio');
+        if (!el) throw new Error('no core audio element');
+        _elCtx = new AudioContext();
+        _elSource = _elCtx.createMediaElementSource(el);
+        _elSource.connect(_elCtx.destination);
+        _elTap = _makeTap(_elCtx);
+        await _elTap.attach(_elSource);
+    }
+
+    // ── Engagement state machine ─────────────────────────────────────────────
+    // 'off' | 'element' | 'stems'
+    let _mode = 'off';
+    let _stemsGraph = null;   // { context, masterNode } snapshot while engaged
+    let _stemsTap = null;
+    const _stemsTaps = new WeakMap();  // context → tap (stems ctx is reused across songs)
+    let _busy = false;
+
+    async function _setSink(ctx, exclusive) {
+        if (typeof ctx.setSinkId !== 'function') throw new Error('setSinkId unsupported');
+        await ctx.setSinkId(exclusive ? { type: 'none' } : '');
+        if (ctx.state !== 'running') await ctx.resume().catch(() => {});
+    }
+
+    async function _disengage() {
+        if (_mode === 'off') return;
+        const prev = _mode;
+        _mode = 'off';
+        try { await api.setRendererBus(false, 0); } catch (_) { /* engine gone */ }
+        if (prev === 'element' && _elCtx) {
+            _elTap.active = false;
+            await _setSink(_elCtx, false).catch(() => {});
+        } else if (prev === 'stems' && _stemsGraph) {
+            if (_stemsTap) _stemsTap.detach(_stemsGraph.masterNode);
+            await _setSink(_stemsGraph.context, false).catch(() => {});
+            _stemsGraph = null; _stemsTap = null;
+        }
+        console.log('[renderer-bus] disengaged (' + prev + ')');
+    }
+
+    async function _engageStems(graph) {
+        await _setSink(graph.context, true);
+        let tap = _stemsTaps.get(graph.context);
+        if (!tap) { tap = _makeTap(graph.context); _stemsTaps.set(graph.context, tap); }
+        await tap.attach(graph.masterNode);
+        await api.setRendererBus(true, 1.0);
+        tap.active = true;
+        _stemsGraph = graph; _stemsTap = tap;
+        _mode = 'stems';
+        console.log('[renderer-bus] engaged: stems graph → engine bus');
+    }
+
+    async function _engageElement() {
+        await _ensureElementCapture();
+        await _setSink(_elCtx, true);
+        await api.setRendererBus(true, 1.0);
+        _elTap.active = true;
+        _mode = 'element';
+        console.log('[renderer-bus] engaged: <audio> element → engine bus');
+    }
+
+    async function _reevaluate() {
+        if (_busy) return;
+        _busy = true;
+        try {
+            let running = false, exclusive = false;
+            try {
+                running = await api.isAudioRunning();
+            } catch (_) { /* engine unreachable → treat as not running */ }
+            if (running) {
+                // Reuse the Phase 1 predicate installed by the routing watcher
+                // (getCurrentDevice + exclusive-type check with change-logged
+                // diagnostics). Fail closed if it is somehow absent.
+                exclusive = !!(await window._juceOutputIsExclusive?.());
+            }
+
+            // The stems plugin publishes its live graph while a multi-stem
+            // song is loaded (and removes it on teardown).
+            const stems = (window.feedBack || window.slopsmith)?.stems?.audioGraph || null;
+            // Element songs: a song is loaded, it is NOT riding the native
+            // transport (Phase 1 owns those), and the stems graph is not the
+            // player. Covers native-transport rejects (codec) in exclusive
+            // mode — without this they would be silent.
+            const songAudio = window._currentSongAudio;
+            const elementSong = !!songAudio && !window._juceMode && !stems;
+
+            let want = 'off';
+            if (running && exclusive) {
+                if (stems) want = 'stems';
+                else if (elementSong) want = 'element';
+            }
+
+            const stemsGraphChanged = _mode === 'stems' && stems !== _stemsGraph;
+            if (want !== _mode || stemsGraphChanged) {
+                await _disengage();
+                if (want === 'stems') await _engageStems(stems);
+                else if (want === 'element') await _engageElement();
+            }
+        } catch (e) {
+            console.warn('[renderer-bus] reevaluate failed (will retry):', e);
+            _mode = 'off';
+        } finally {
+            _busy = false;
+        }
+    }
+
+    // Same cadence/rationale as the routing watcher above. Also re-check on
+    // visibility return so a device switch made while hidden is reconciled.
+    setInterval(() => { if (!document.hidden) void _reevaluate(); }, 500);
+    document.addEventListener('visibilitychange', () => { if (!document.hidden) void _reevaluate(); });
+    window._reevaluateRendererBus = _reevaluate;
+})();
+
 // Desktop JUCE backing uses an empty <audio> element; plugins such as Section Map
 // still seek via audio.currentTime / pause / play. Mirror those onto jucePlayer
 // while _juceMode is active. Same-tick pause+seek coalesce into a single seek
@@ -11563,6 +11837,14 @@ async function loadPlugins() {
                         // URL ?v=mtime convention elsewhere in this file).
                         const v = encodeURIComponent(wantedVersion);
                         script.src = `/api/plugins/${plugin.id}/screen.js${v ? `?v=${v}` : ''}`;
+                        // Module-migration (R0): a migrated plugin declares
+                        // scriptType:"module" and its screen.js is `import
+                        // './src/main.js'`. A <script type="module"> fires load
+                        // only after its whole static-import graph evaluates, so
+                        // the await-onload completion + _loadingPluginId contract
+                        // below is preserved (a classic-IIFE dynamic import()
+                        // would not). Classic plugins are unaffected.
+                        if (plugin.script_type === 'module') script.type = 'module';
                         script.dataset.pluginId = plugin.id;
                         script.dataset.pluginVersion = wantedVersion;
                         window.feedBack._loadingPluginId = plugin.id;

static/highway.js

@@ -3409,21 +3409,57 @@ function createHighway() {
                                 if (msg.audio_url) {
                                     const audio = document.getElementById('audio');
                                     const audioFilename = msg.audio_url.split('/').pop();
-                                    // Only attempt JUCE routing for /audio/ URLs — sloppak stems
-                                    // (/api/sloppak/…) are not resolvable via audio-local-path.
+                                    // /audio/ URLs are always JUCE-routable. A feedpak full-mix
+                                    // (single-mix pack: original audio, no stems) is routable too,
+                                    // but ONLY under an exclusive-style output — the actual
+                                    // exclusive check happens at routing time (app.js watcher /
+                                    // the async block below), not here, because the share mode
+                                    // can change while the song is loaded. Sloppak stem URLs are
+                                    // never routable.
                                     const isAudioUrl = msg.audio_url.startsWith('/audio/');
+                                    // "Full mix" covers BOTH single-mix pack shapes:
+                                    //  - stem-less packs (original_audio: in the manifest,
+                                    //    audio_url == original_audio_url), and
+                                    //  - single-stem packs (stems: [full.ogg] only) — the server
+                                    //    puts the full mix in the stems list, has_original_audio
+                                    //    is false, and audio_url points at the one stem. With one
+                                    //    stem there is no per-stem mix to preserve, so routing it
+                                    //    natively loses nothing. Real multi-stem (>1) stays out
+                                    //    until Phase 2.
+                                    const isFeedpakFullMix = !isAudioUrl
+                                        && msg.audio_url.startsWith('/api/sloppak/')
+                                        && ((!!msg.has_original_audio && !msg.has_stems)
+                                            || (msg.stems || []).length === 1);
                                     // Record the loaded song's audio so app.js can re-route it
                                     // between the HTML5 and JUCE paths if the audio engine is
                                     // started/stopped after the song is already loaded. Set this
                                     // unconditionally (not just on reload): when alreadyLoaded is
                                     // true the watcher must still see correct, current metadata.
-                                    window._currentSongAudio = { url: msg.audio_url, juceEligible: isAudioUrl };
+                                    window._currentSongAudio = {
+                                        url: msg.audio_url,
+                                        juceEligible: isAudioUrl,
+                                        feedpakFullMix: isFeedpakFullMix,
+                                    };
                                     const alreadyLoaded = window._juceMode
                                         ? window._juceAudioUrl === msg.audio_url
                                         : (audio.src && audio.src.includes(audioFilename));
+                                    // [feedpak-route] diagnostics: every eligibility input in one
+                                    // line — shows up in the exported diagnostics bundle. If
+                                    // has_stems is true the pack is multi-stem and Phase 1
+                                    // deliberately does not route it (Phase 2 work).
+                                    console.log('[feedpak-route] song-load:',
+                                        'url=', msg.audio_url,
+                                        'isAudioUrl=', isAudioUrl,
+                                        'isFeedpakFullMix=', isFeedpakFullMix,
+                                        'has_stems=', !!msg.has_stems,
+                                        'stems=', (msg.stems || []).length,
+                                        'has_original_audio=', !!msg.has_original_audio,
+                                        'format=', msg.format,
+                                        'alreadyLoaded=', alreadyLoaded,
+                                        'juceApi=', !!window.feedBackDesktop?.audio);
                                     if (!alreadyLoaded) {
                                         const juceApi = window.feedBackDesktop?.audio;
-                                        if (isAudioUrl && juceApi) {
+                                        if ((isAudioUrl || isFeedpakFullMix) && juceApi) {
                                             // Run JUCE routing off the critical message-processing chain
                                             // so subsequent notes/chords/ready messages aren't blocked
                                             // waiting for IPC + HTTP round-trips. The 'ready' handler
@@ -3466,7 +3502,24 @@ function createHighway() {
                                                         clearTimeout(barrierTimer);
                                                         if (gen !== _wsGen) return; // navigated away during the wait
                                                     }
-                                                    if (await juceApi.isAudioRunning()) {
+                                                    // Feedpak full-mix rides the engine ONLY under an
+                                                    // exclusive-style output (shared mode falls through to
+                                                    // the HTML5 fallback below, keeping the WebAudio path
+                                                    // fully working). /audio/ songs route whenever the
+                                                    // engine runs, as before. If the share mode changes
+                                                    // later, the app.js watcher re-evaluates and migrates.
+                                                    let routeToJuce = await juceApi.isAudioRunning();
+                                                    console.log('[feedpak-route] initial-load: engineRunning=', routeToJuce);
+                                                    if (routeToJuce) {
+                                                        if (gen !== _wsGen) return; // stale
+                                                        if (isFeedpakFullMix) {
+                                                            const exclFn = window._juceOutputIsExclusive;
+                                                            routeToJuce = !!(await exclFn?.());
+                                                            console.log('[feedpak-route] initial-load: feedpak exclusive check →',
+                                                                routeToJuce, '(predicate installed=', typeof exclFn === 'function', ')');
+                                                        }
+                                                    }
+                                                    if (routeToJuce) {
                                                         if (gen !== _wsGen) return; // stale
                                                         const res = await fetch(`/api/audio-local-path?url=${encodeURIComponent(audioUrl)}`);
                                                         if (!res.ok) throw new Error('HTTP ' + res.status);

static/index.html

@@ -119,6 +119,8 @@
                         <option value="year-desc">Year (newest)</option>
                         <option value="year">Year (oldest)</option>
                         <option value="tuning">Tuning</option>
+                        <option value="difficulty">Difficulty (easiest first)</option>
+                        <option value="difficulty-desc">Difficulty (hardest first)</option>
                     </select>
                     <!-- Format filter (shared) -->
                     <select id="lib-format" onchange="sortLibrary()"

static/v3/songs.js

@@ -38,6 +38,9 @@
         // Mastery = best accuracy across arrangements (song_stats); unscored songs
         // sort last either way. Ascending surfaces what needs work; never default.
         ['mastery', 'Needs practice first'], ['mastery-desc', 'Most mastered first'],
+        // Personal difficulty (song_user_meta.user_difficulty, 1-5); unrated
+        // songs sort last either way.
+        ['difficulty', 'Difficulty (easiest first)'], ['difficulty-desc', 'Difficulty (hardest first)'],
     ];
     const FORMATS = [['', 'All formats'], ['sloppak', 'Feedpak'], ['loose', 'Folder']];
     const ARRANGEMENTS = ['Lead', 'Rhythm', 'Bass', 'Combo', 'Vocals'];

tests/js/juce_engine_reroute.test.js

@@ -40,7 +40,7 @@ function extractWatcherIIFE(src) {
 
 // Build a sandbox with fakes and run the watcher IIFE inside it. Returns the
 // sandbox so tests can drive window._reevaluateJuceRouting and inspect state.
-function makeSandbox({ isAudioRunning, loadBackingTrack }) {
+function makeSandbox({ isAudioRunning, loadBackingTrack, outputType = 'Windows Audio' }) {
     const calls = { loadBackingTrack: [], jucePlay: 0, jucePause: 0, audioPlay: 0 };
 
     const audio = {
@@ -65,6 +65,7 @@ function makeSandbox({ isAudioRunning, loadBackingTrack }) {
     const juceApi = {
         isAudioRunning: () => Promise.resolve(isAudioRunning()),
         loadBackingTrack: (p) => { calls.loadBackingTrack.push(p); return Promise.resolve(loadBackingTrack()); },
+        getCurrentDevice: () => Promise.resolve({ outputType: typeof outputType === 'function' ? outputType() : outputType }),
         getBackingDuration: () => Promise.resolve(180),
         seekBacking: () => Promise.resolve(),
         startBacking: () => Promise.resolve(),
@@ -152,6 +153,87 @@ test('non-JUCE-eligible song (sloppak stems) is never rerouted', async () => {
     assert.equal(sb.__calls.loadBackingTrack.length, 0);
 });
 
+test('feedpak full-mix + exclusive output → migrates to JUCE', async () => {
+    const sb = makeSandbox({
+        isAudioRunning: () => true,
+        loadBackingTrack: () => true,
+        outputType: 'Windows Audio (Exclusive Mode)',
+    });
+    sb.window._juceMode = false;
+    sb.window._currentSongAudio = {
+        url: '/api/sloppak/song.sloppak/file/stems/full.ogg',
+        juceEligible: false,
+        feedpakFullMix: true,
+    };
+
+    await sb.window._reevaluateJuceRouting();
+
+    assert.equal(sb.window._juceMode, true, 'feedpak full-mix rides the engine under exclusive output');
+    assert.equal(sb.__calls.loadBackingTrack.length, 1);
+});
+
+test('feedpak full-mix + ASIO output → migrates to JUCE', async () => {
+    const sb = makeSandbox({
+        isAudioRunning: () => true,
+        loadBackingTrack: () => true,
+        outputType: 'ASIO',
+    });
+    sb.window._juceMode = false;
+    sb.window._currentSongAudio = {
+        url: '/api/sloppak/song.sloppak/file/stems/full.ogg',
+        juceEligible: false,
+        feedpakFullMix: true,
+    };
+
+    await sb.window._reevaluateJuceRouting();
+
+    assert.equal(sb.window._juceMode, true, 'ASIO is exclusive-style; feedpak rides the engine');
+});
+
+test('feedpak full-mix + shared output → stays on HTML5 (stem mixer untouched)', async () => {
+    for (const shared of ['Windows Audio', 'Windows Audio (Low Latency Mode)', 'DirectSound']) {
+        const sb = makeSandbox({
+            isAudioRunning: () => true,
+            loadBackingTrack: () => true,
+            outputType: shared,
+        });
+        sb.window._juceMode = false;
+        sb.window._currentSongAudio = {
+            url: '/api/sloppak/song.sloppak/file/stems/full.ogg',
+            juceEligible: false,
+            feedpakFullMix: true,
+        };
+
+        await sb.window._reevaluateJuceRouting();
+
+        assert.equal(sb.window._juceMode, false, `stays on HTML5 for shared type "${shared}"`);
+        assert.equal(sb.__calls.loadBackingTrack.length, 0);
+    }
+});
+
+test('feedpak on JUCE + output leaves exclusive mode → migrates back to HTML5', async () => {
+    let type = 'Windows Audio (Exclusive Mode)';
+    const sb = makeSandbox({
+        isAudioRunning: () => true,
+        loadBackingTrack: () => true,
+        outputType: () => type,
+    });
+    const url = '/api/sloppak/song.sloppak/file/stems/full.ogg';
+    sb.window._juceMode = true;
+    sb.window._juceAudioUrl = url;
+    sb.window._currentSongAudio = { url, juceEligible: false, feedpakFullMix: true };
+
+    // Still exclusive: routing is consistent, no switch.
+    await sb.window._reevaluateJuceRouting();
+    assert.equal(sb.window._juceMode, true, 'consistent while exclusive');
+
+    // Device switched to shared mid-song: must return to HTML5.
+    type = 'Windows Audio';
+    await sb.window._reevaluateJuceRouting();
+    assert.equal(sb.window._juceMode, false, 'returned to HTML5 after leaving exclusive mode');
+    assert.equal(sb.audio.src, url, 'HTML5 element re-pointed at the song');
+});
+
 test('JUCE hard-reject is memoised → not retried on the next poll', async () => {
     const sb = makeSandbox({ isAudioRunning: () => true, loadBackingTrack: () => false });
     sb.window._juceMode = false;

tests/js/plugin_loader_script_type.test.js

@@ -0,0 +1,59 @@
+// Guards the R0 module-migration loader change in static/app.js: a migrated
+// plugin (manifest scriptType:"module", surfaced as plugin.script_type) must be
+// injected as <script type="module"> so its screen.js `import './src/main.js'`
+// graph loads, while classic plugins stay untouched.
+//
+// The injection is a single line inside the large async loadPlugins() closure
+// (it depends on loadedScripts, _removePluginScriptTags, and the
+// _loadingPluginId completion window), so a faithful behavioural harness would
+// need to stub the whole loader. Instead this asserts the *structural*
+// contract in source — the guard exists, is gated (not unconditional), and sits
+// inside the screen.js injection block before appendChild. The behavioural proof
+// is the R0 end-to-end live-edit check (a real module plugin booting in-browser).
+
+const { test } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+
+const APP_JS = path.join(__dirname, '..', '..', 'static', 'app.js');
+const src = fs.readFileSync(APP_JS, 'utf8');
+
+// Isolate the screen.js <script> injection block: from where its src is built
+// to where the element is appended.
+function injectionBlock() {
+    const start = src.indexOf('/api/plugins/${plugin.id}/screen.js');
+    assert.ok(start !== -1, 'screen.js injection src not found — loader moved?');
+    const end = src.indexOf('document.body.appendChild(script)', start);
+    assert.ok(end !== -1, 'appendChild(script) not found after screen.js src');
+    return src.slice(start, end);
+}
+
+test('module plugins are injected as <script type="module">', () => {
+    const block = injectionBlock();
+    assert.match(
+        block,
+        /if\s*\(\s*plugin\.script_type\s*===\s*['"]module['"]\s*\)\s*script\.type\s*=\s*['"]module['"]\s*;/,
+        'expected a guarded `script.type = "module"` keyed on plugin.script_type === "module"',
+    );
+});
+
+test('the module type is gated, never set unconditionally', () => {
+    const block = injectionBlock();
+    // Every assignment of script.type in the block must be on the same line as
+    // the plugin.script_type guard (i.e. no bare `script.type = 'module'`).
+    for (const line of block.split('\n')) {
+        if (/script\.type\s*=/.test(line)) {
+            assert.match(line, /plugin\.script_type\s*===\s*['"]module['"]/,
+                `unguarded script.type assignment: ${line.trim()}`);
+        }
+    }
+});
+
+test('the module guard sits before appendChild, after the src assignment', () => {
+    const guardAt = src.indexOf('script.type = \'module\'');
+    const srcAt = src.indexOf('/api/plugins/${plugin.id}/screen.js');
+    const appendAt = src.indexOf('document.body.appendChild(script)', srcAt);
+    assert.ok(guardAt > srcAt && guardAt < appendAt,
+        'the module guard must live inside the screen.js injection block');
+});

tests/js/renderer_bus_feeder.test.js

@@ -0,0 +1,195 @@
+// Behavioral tests for the renderer-audio bus feeder in static/app.js.
+//
+// The feeder (an IIFE, `_installRendererBusFeeder`) captures renderer-side
+// song audio (stems-plugin WebAudio master, or the core <audio> element) and
+// pushes it into the desktop engine's renderer bus while the output device is
+// exclusive-style — the Phase 2 path for audio the native backing transport
+// cannot carry. These tests extract that IIFE from source and exercise
+// `window._reevaluateRendererBus` against fakes, covering: stems engagement
+// under exclusive output, disengagement on return to shared mode, inertness
+// in shared mode / while the native transport owns the song, and the
+// element-capture fallback.
+
+const { test } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+const vm = require('node:vm');
+
+const APP_JS = path.join(__dirname, '..', '..', 'static', 'app.js');
+
+function extractFeederIIFE(src) {
+    const marker = '(function _installRendererBusFeeder() {';
+    const start = src.indexOf(marker);
+    assert.ok(start !== -1, 'feeder IIFE not found in app.js');
+    const openBrace = src.indexOf('{', start);
+    let depth = 1;
+    let i = openBrace + 1;
+    while (i < src.length && depth > 0) {
+        const ch = src[i];
+        if (ch === '{') depth++;
+        else if (ch === '}') depth--;
+        i++;
+    }
+    assert.ok(depth === 0, 'unbalanced braces in feeder IIFE');
+    const tail = src.slice(i, i + 5);
+    assert.match(tail, /^\)\(\)/, 'feeder IIFE not immediately invoked');
+    return src.slice(start, i) + ')();';
+}
+
+function makeFakeContext(sampleRate = 48000) {
+    const ctx = {
+        sampleRate,
+        state: 'running',
+        sinkIdCalls: [],
+        destination: { isDestination: true },
+        setSinkId(v) { this.sinkIdCalls.push(v); return Promise.resolve(); },
+        resume() { this.state = 'running'; return Promise.resolve(); },
+        audioWorklet: { addModule: () => Promise.resolve() },
+        createMediaElementSource(el) {
+            this.mediaSourceEl = el;
+            return { connect() {}, disconnect() {} };
+        },
+    };
+    return ctx;
+}
+
+function makeSandbox({ isAudioRunning = () => true, exclusive = () => true } = {}) {
+    const calls = { setRendererBus: [], pushRendererAudio: [] };
+
+    const api = {
+        isAudioRunning: () => Promise.resolve(isAudioRunning()),
+        setRendererBus: (en, g) => { calls.setRendererBus.push([en, g]); return Promise.resolve(); },
+        pushRendererAudio: (buf, rate) => { calls.pushRendererAudio.push([buf.length, rate]); },
+    };
+
+    class FakeWorkletNode {
+        constructor() { this.port = { onmessage: null }; }
+        connect() {}
+        disconnect() {}
+    }
+
+    const sandbox = {
+        console: { log() {}, warn() {}, error() {} },
+        URL: { createObjectURL: () => 'blob:tap', revokeObjectURL() {} },
+        Blob: class { constructor() {} },
+        AudioWorkletNode: FakeWorkletNode,
+        AudioContext: function () { const c = makeFakeContext(); sandbox.__createdContexts.push(c); return c; },
+        WeakSet, WeakMap, Promise, Float32Array, Math,
+        setInterval: () => 0,
+        document: {
+            hidden: false,
+            addEventListener() {},
+            getElementById: () => sandbox.__audioEl,
+        },
+        __createdContexts: [],
+        __audioEl: { id: 'audio' },
+        __calls: calls,
+        window: null,
+    };
+    sandbox.window = {
+        feedBackDesktop: { audio: api },
+        _juceOutputIsExclusive: () => Promise.resolve(exclusive()),
+        _juceMode: false,
+        _currentSongAudio: null,
+        feedBack: { stems: {} },
+    };
+    sandbox.globalThis = sandbox;
+
+    const src = fs.readFileSync(APP_JS, 'utf8');
+    vm.createContext(sandbox);
+    vm.runInContext(extractFeederIIFE(src), sandbox);
+    assert.equal(typeof sandbox.window._reevaluateRendererBus, 'function',
+        'feeder must expose window._reevaluateRendererBus');
+    return sandbox;
+}
+
+function makeStemsGraph() {
+    return {
+        context: makeFakeContext(),
+        masterNode: { connect() {}, disconnect() {} },
+    };
+}
+
+test('stems graph + exclusive output → bus enabled, stems ctx null-sinked', async () => {
+    const sb = makeSandbox({ exclusive: () => true });
+    const graph = makeStemsGraph();
+    sb.window.feedBack.stems.audioGraph = graph;
+
+    await sb.window._reevaluateRendererBus();
+
+    assert.deepEqual(sb.__calls.setRendererBus.at(-1), [true, 1.0], 'bus enabled');
+    assert.equal(graph.context.sinkIdCalls.at(-1)?.type, 'none', 'stems ctx re-pointed at null sink');
+});
+
+test('output returns to shared → bus disabled, sink restored', async () => {
+    let excl = true;
+    const sb = makeSandbox({ exclusive: () => excl });
+    const graph = makeStemsGraph();
+    sb.window.feedBack.stems.audioGraph = graph;
+
+    await sb.window._reevaluateRendererBus();
+    excl = false;
+    await sb.window._reevaluateRendererBus();
+
+    assert.deepEqual(sb.__calls.setRendererBus.at(-1), [false, 0], 'bus disabled');
+    assert.equal(graph.context.sinkIdCalls.at(-1), '', 'default sink restored');
+});
+
+test('stems graph + shared output → feeder stays off (no double audio)', async () => {
+    const sb = makeSandbox({ exclusive: () => false });
+    sb.window.feedBack.stems.audioGraph = makeStemsGraph();
+
+    await sb.window._reevaluateRendererBus();
+
+    assert.equal(sb.__calls.setRendererBus.length, 0, 'bus never touched in shared mode');
+});
+
+test('element song + exclusive → element captured into bus', async () => {
+    const sb = makeSandbox({ exclusive: () => true });
+    sb.window._currentSongAudio = { url: '/api/sloppak/x.sloppak/file/stems/full.ogg' };
+    sb.window._juceMode = false;
+
+    await sb.window._reevaluateRendererBus();
+
+    assert.equal(sb.__createdContexts.length, 1, 'capture context created');
+    assert.equal(sb.__createdContexts[0].mediaSourceEl, sb.__audioEl, 'element source captured');
+    assert.deepEqual(sb.__calls.setRendererBus.at(-1), [true, 1.0], 'bus enabled');
+});
+
+test('song riding the native transport (_juceMode) → feeder stays off', async () => {
+    const sb = makeSandbox({ exclusive: () => true });
+    sb.window._currentSongAudio = { url: '/audio/song.ogg' };
+    sb.window._juceMode = true;
+
+    await sb.window._reevaluateRendererBus();
+
+    assert.equal(sb.__calls.setRendererBus.length, 0, 'native transport owns the song');
+    assert.equal(sb.__createdContexts.length, 0, 'no capture context created');
+});
+
+test('stems graph replaced mid-engagement → re-engages on the new graph', async () => {
+    const sb = makeSandbox({ exclusive: () => true });
+    const g1 = makeStemsGraph();
+    sb.window.feedBack.stems.audioGraph = g1;
+    await sb.window._reevaluateRendererBus();
+
+    const g2 = makeStemsGraph();
+    sb.window.feedBack.stems.audioGraph = g2;
+    await sb.window._reevaluateRendererBus();
+
+    assert.equal(g2.context.sinkIdCalls.at(-1)?.type, 'none', 'new graph null-sinked');
+    assert.deepEqual(sb.__calls.setRendererBus.at(-1), [true, 1.0], 're-enabled for new graph');
+});
+
+test('engine stops → bus disabled', async () => {
+    let running = true;
+    const sb = makeSandbox({ isAudioRunning: () => running, exclusive: () => true });
+    sb.window.feedBack.stems.audioGraph = makeStemsGraph();
+    await sb.window._reevaluateRendererBus();
+
+    running = false;
+    await sb.window._reevaluateRendererBus();
+
+    assert.deepEqual(sb.__calls.setRendererBus.at(-1), [false, 0], 'bus disabled after engine stop');
+});

tests/test_appstate.py

@@ -0,0 +1,153 @@
+"""The router seam (`appstate.py`).
+
+The load-bearing assertion here is `test_server_wires_the_seam`: that `server`
+actually calls `appstate.configure(...)`. Every other test in this file would
+pass just fine against a seam nothing ever wires up — the same class of silent
+no-op that bit the frontend refactor twice when a scripted `setHostHooks` edit
+stopped matching its anchor. Unit tests cannot see wiring unless you make them
+look at it.
+"""
+
+import importlib
+import sys
+
+import pytest
+
+import appstate
+
+
+def _close_server_dbs(mod):
+    conn = getattr(getattr(mod, "meta_db", None), "conn", None)
+    if conn is not None:
+        getattr(mod, "_join_background_db_threads", lambda: None)()
+        conn.close()
+    ae_conn = getattr(getattr(mod, "audio_effect_mappings", None), "conn", None)
+    if ae_conn is not None:
+        ae_conn.close()
+
+
+@pytest.fixture()
+def isolated_server(tmp_path, monkeypatch):
+    """A freshly imported `server` bound to a throwaway CONFIG_DIR.
+
+    Importing `server` constructs `MetadataDB` + `AudioEffectsMappingDB` at
+    module level, so it MUST be re-imported under a patched CONFIG_DIR — an
+    unguarded `import server` would create/mutate the developer's real
+    `~/.local/share/feedback` databases. Same idiom as the other ~49
+    server-importing suites.
+
+    Teardown restores the appstate slots as well as closing the connections:
+    leaving `appstate.meta_db` published but pointing at a closed sqlite handle
+    would hand a later test (or router) a live-looking, dead singleton.
+    """
+    previous = (appstate.meta_db, appstate.audio_effect_mappings)
+    monkeypatch.setenv("CONFIG_DIR", str(tmp_path))
+    sys.modules.pop("server", None)
+    mod = importlib.import_module("server")
+    yield mod
+    _close_server_dbs(mod)
+    # Leave no half-torn-down `server` behind: the next fixture re-imports it.
+    sys.modules.pop("server", None)
+    appstate.configure(meta_db=previous[0], audio_effect_mappings=previous[1])
+
+
+def test_import_is_side_effect_free():
+    """`import appstate` must construct nothing and touch no disk.
+
+    This is why the ~49 fixtures that `sys.modules.pop("server")` and re-import
+    (to rebuild `meta_db` under a patched CONFIG_DIR) keep working untouched:
+    server owns construction, appstate only mirrors it. A singleton *owned*
+    here would survive that pop and go stale.
+    """
+    sys.modules.pop("appstate", None)
+    fresh = importlib.import_module("appstate")
+    try:
+        assert fresh.meta_db is None
+        assert fresh.audio_effect_mappings is None
+    finally:
+        sys.modules["appstate"] = appstate
+
+
+def test_configure_publishes_known_slots():
+    sentinel = object()
+    original = appstate.meta_db
+    try:
+        appstate.configure(meta_db=sentinel)
+        assert appstate.meta_db is sentinel
+    finally:
+        appstate.configure(meta_db=original)
+
+
+def test_configure_is_idempotent():
+    """server re-imports call configure() again; the last write must win."""
+    original = appstate.meta_db
+    try:
+        appstate.configure(meta_db="first")
+        appstate.configure(meta_db="second")
+        assert appstate.meta_db == "second"
+    finally:
+        appstate.configure(meta_db=original)
+
+
+def test_configure_rejects_an_unknown_slot():
+    """A typo'd or stale keyword must raise, not silently create a global that
+    nothing reads. A seam whose wiring can no-op undetected is worse than none."""
+    with pytest.raises(TypeError, match="unknown slot"):
+        appstate.configure(met_db="typo")
+    assert not hasattr(appstate, "met_db")
+
+
+def test_late_bound_read_sees_a_later_configure():
+    """Routers must read `appstate.meta_db`, never `from appstate import meta_db`.
+    This pins the property that makes that rule work."""
+    def router_style_read():
+        return appstate.meta_db          # module attribute, resolved at call time
+
+    original = appstate.meta_db
+    try:
+        appstate.configure(meta_db="before")
+        assert router_style_read() == "before"
+        appstate.configure(meta_db="after")
+        assert router_style_read() == "after"
+    finally:
+        appstate.configure(meta_db=original)
+
+
+def test_server_wires_the_seam(isolated_server):
+    """The one that catches a dropped `appstate.configure(...)` call.
+
+    Identity, not truthiness, so a stray re-assignment or a half-applied edit
+    fails here rather than in some router months later.
+    """
+    assert appstate.meta_db is isolated_server.meta_db
+    assert appstate.audio_effect_mappings is isolated_server.audio_effect_mappings
+    assert appstate.meta_db is not None
+
+
+def test_reimporting_server_republishes_the_fresh_singletons(
+    isolated_server, tmp_path, monkeypatch
+):
+    """The 49-fixture contract, exercised end to end.
+
+    Those fixtures `sys.modules.pop("server")` + re-import to rebuild `meta_db`
+    under a new CONFIG_DIR, and know nothing about appstate. So the seam must
+    re-publish on that second import. This is the test that would fail if
+    `appstate` ever *owned* the singletons: a module-level `meta_db` there
+    survives the pop and the assertions below would still see the FIRST DB.
+    """
+    first_db = isolated_server.meta_db
+    assert appstate.meta_db is first_db
+    assert str(tmp_path) in first_db.db_path
+
+    second_config = tmp_path / "second"
+    monkeypatch.setenv("CONFIG_DIR", str(second_config))
+    sys.modules.pop("server", None)
+    second_server = importlib.import_module("server")
+    try:
+        assert second_server.meta_db is not first_db          # genuinely rebuilt
+        assert str(second_config) in second_server.meta_db.db_path
+        assert appstate.meta_db is second_server.meta_db      # ...and re-published
+        assert appstate.audio_effect_mappings is second_server.audio_effect_mappings
+    finally:
+        _close_server_dbs(second_server)
+        sys.modules.pop("server", None)

tests/test_audio_local_path.py

@@ -103,12 +103,98 @@ def test_returns_404_for_nonexistent_file(client_and_server):
     assert "error" in r.json()
 
 
-# ── rejected non-/audio/ inputs ───────────────────────────────────────────────
+# ── sloppak URLs (feedpak full-mix, desktop exclusive-mode routing) ──────────
 
-def test_rejects_sloppak_url(client_and_server):
+@pytest.fixture()
+def dlc_client(tmp_path, monkeypatch):
+    """Loopback TestClient with a temp DLC_DIR for sloppak resolution."""
+    dlc = tmp_path / "dlc"
+    dlc.mkdir()
+    monkeypatch.setenv("DLC_DIR", str(dlc))
+    monkeypatch.setenv("CONFIG_DIR", str(tmp_path / "cfg"))
+    monkeypatch.setenv("FEEDBACK_SYNC_STARTUP", "1")
+    sys.modules.pop("server", None)
+    server = importlib.import_module("server")
+    # Module-level sloppak source-dir cache survives re-import; clear it so a
+    # prior test's filename key can't shadow this test's temp DLC_DIR.
+    server.sloppak_mod._source_cache.clear()
+    monkeypatch.setattr(server, "load_plugins", lambda *a, **kw: None)
+    monkeypatch.setattr(server, "startup_scan", lambda: None)
+    static_tmp = tmp_path / "static"
+    static_tmp.mkdir()
+    monkeypatch.setattr(server, "STATIC_DIR", static_tmp)
+    tc = TestClient(server.app, client=("127.0.0.1", 50000))
+    try:
+        yield tc, server, dlc
+    finally:
+        tc.close()
+        meta_db = getattr(server, "meta_db", None)
+        conn = getattr(meta_db, "conn", None)
+        if conn is not None:
+            getattr(__import__("sys").modules.get("server"), "_join_background_db_threads", lambda: None)()
+            conn.close()
+
+
+def _make_sloppak(dlc, name="song.sloppak"):
+    """Create a minimal directory-form sloppak with a full-mix file."""
+    pak = dlc / name
+    (pak / "stems").mkdir(parents=True)
+    (pak / "stems" / "full.ogg").write_bytes(b"OggS-fake")
+    return pak
+
+
+def test_sloppak_url_resolves_to_local_path(dlc_client):
+    tc, _server, dlc = dlc_client
+    pak = _make_sloppak(dlc)
+    r = tc.get(
+        "/api/audio-local-path",
+        params={"url": "/api/sloppak/song.sloppak/file/stems/full.ogg"},
+    )
+    assert r.status_code == 200, r.text
+    assert r.json()["path"] == str((pak / "stems" / "full.ogg").resolve())
+
+
+def test_sloppak_url_percent_encoded_segments_decode(dlc_client):
+    tc, _server, dlc = dlc_client
+    _make_sloppak(dlc, name="My Song.sloppak")
+    r = tc.get(
+        "/api/audio-local-path",
+        params={"url": "/api/sloppak/My%20Song.sloppak/file/stems/full.ogg"},
+    )
+    assert r.status_code == 200, r.text
+
+
+def test_sloppak_url_rel_traversal_is_403(dlc_client):
+    tc, _server, dlc = dlc_client
+    _make_sloppak(dlc)
+    (dlc / "secret.txt").write_text("top secret")
+    r = tc.get(
+        "/api/audio-local-path",
+        params={"url": "/api/sloppak/song.sloppak/file/..%2Fsecret.txt"},
+    )
+    assert r.status_code == 403, r.text
+
+
+def test_sloppak_url_filename_traversal_is_403(dlc_client):
+    tc, _server, _dlc = dlc_client
+    r = tc.get(
+        "/api/audio-local-path",
+        params={"url": "/api/sloppak/..%2F..%2F..%2Fetc/file/passwd"},
+    )
+    assert r.status_code == 403, r.text
+
+
+def test_sloppak_url_without_dlc_configured_is_404(client_and_server):
+    """No DLC_DIR in the base fixture — resolver reports 'not configured'."""
     client, _ = client_and_server
-    r = client.get("/api/audio-local-path", params={"url": "/api/sloppak/mysong/file/stems/full.ogg"})
-    assert r.status_code == 400
+    r = client.get(
+        "/api/audio-local-path",
+        params={"url": "/api/sloppak/mysong/file/stems/full.ogg"},
+    )
+    assert r.status_code == 404
+
+
+# ── rejected non-/audio/ inputs ───────────────────────────────────────────────
 
 
 def test_rejects_empty_url(client_and_server):

tests/test_gp2rs.py

@@ -121,7 +121,10 @@ def _converter_ebeats(converter, numerator, denominator, tempo_changes=None):
 def _assert_ebeats(converter, numerator, denominator, expected_times, tempo_changes=None):
     ebeats = _converter_ebeats(converter, numerator, denominator, tempo_changes)
 
-    assert [ebeat.get("time") for ebeat in ebeats] == expected_times
+    # Compare by value, not string: beat times are written at 6-decimal
+    # (microsecond) precision so the derived per-bar tempo matches the authored
+    # GP value, but these tests only care about the spacing, not the format.
+    assert [float(ebeat.get("time")) for ebeat in ebeats] == [float(t) for t in expected_times]
     assert [ebeat.get("measure") for ebeat in ebeats] == [
         "1",
         *["-1"] * (len(expected_times) - 1),

tests/test_gp2rs_drums.py

@@ -223,15 +223,15 @@ def test_unmapped_percussion_silently_skipped(monkeypatch):
 
 def test_unmapped_percussion_reported_via_out_unmapped(monkeypatch):
     """Opting in via out_unmapped records the dropped MIDI notes (count +
-    times) so a caller can surface a warning / mapping UI."""
+    times + velocities) so a caller can surface a warning / mapping UI."""
     _setup(monkeypatch)
     track = _fake_track(
         string_midis=[56, 36, 54],
         beats=[
-            (0.0, [_fake_note(string_idx=1)]),   # cowbell — drop
-            (1.0, [_fake_note(string_idx=2)]),   # kick — keep
-            (1.5, [_fake_note(string_idx=3)]),   # tambourine — drop
-            (2.0, [_fake_note(string_idx=1)]),   # cowbell again — drop
+            (0.0, [_fake_note(string_idx=1, velocity=88)]),  # cowbell — drop
+            (1.0, [_fake_note(string_idx=2)]),               # kick — keep
+            (1.5, [_fake_note(string_idx=3, velocity=25)]),  # tambourine — drop
+            (2.0, [_fake_note(string_idx=1, velocity=44)]),  # cowbell again — drop
         ],
     )
     song = SimpleNamespace(tracks=[track])
@@ -247,6 +247,44 @@ def test_unmapped_percussion_reported_via_out_unmapped(monkeypatch):
     # Times are captured (rounded to 3 dp).
     assert unmapped[56]["times"] == [0.0, 2.0]
     assert unmapped[54]["times"] == [1.5]
+    # Velocities ride index-aligned with times — the mapping UI can carry
+    # the source dynamics through instead of flattening to a default.
+    assert unmapped[56]["velocities"] == [88, 44]
+    assert unmapped[54]["velocities"] == [25]
+
+
+def test_unmapped_velocities_sort_in_lockstep_with_times(monkeypatch):
+    """Multi-voice measures can capture times out of order; the final sort
+    must reorder velocities WITH their times, not leave them behind."""
+    _setup(monkeypatch)
+    track = _fake_track(
+        string_midis=[56],
+        beats=[
+            # Deliberately reversed chronology within the measure.
+            (2.0, [_fake_note(string_idx=1, velocity=44)]),
+            (0.0, [_fake_note(string_idx=1, velocity=88)]),
+        ],
+    )
+    song = SimpleNamespace(tracks=[track])
+    unmapped: dict[int, dict] = {}
+    gp2rs.convert_drum_track_to_drumtab(song, 0, out_unmapped=unmapped)
+    assert unmapped[56]["times"] == [0.0, 2.0]
+    assert unmapped[56]["velocities"] == [88, 44], \
+        "velocity must follow its time through the sort"
+
+
+def test_unmapped_out_of_range_velocity_falls_back_to_default(monkeypatch):
+    """A corrupt/zero GP velocity records the 100 import default rather
+    than poisoning the aligned list."""
+    _setup(monkeypatch)
+    track = _fake_track(
+        string_midis=[56],
+        beats=[(0.0, [_fake_note(string_idx=1, velocity=0)])],
+    )
+    song = SimpleNamespace(tracks=[track])
+    unmapped: dict[int, dict] = {}
+    gp2rs.convert_drum_track_to_drumtab(song, 0, out_unmapped=unmapped)
+    assert unmapped[56]["velocities"] == [100]
 
 
 def test_zero_velocity_omitted_from_wire(monkeypatch):

tests/test_highway_ws_authors.py

@@ -16,6 +16,8 @@ import pytest
 import yaml
 from fastapi.testclient import TestClient
 
+from routers.ws_highway import _sanitize_authors
+
 
 # ── _sanitize_authors unit tests ────────────────────────────────────────────
 
@@ -35,7 +37,7 @@ def server_mod(monkeypatch, tmp_path):
 
 
 def test_sanitize_authors_valid(server_mod):
-    out = server_mod._sanitize_authors(
+    out = _sanitize_authors(
         {
             "authors": [
                 {"name": "Azure", "role": "charter", "email": "a@b.c", "url": "x"},
@@ -53,7 +55,7 @@ def test_sanitize_authors_valid(server_mod):
 
 
 def test_sanitize_authors_skips_malformed(server_mod):
-    out = server_mod._sanitize_authors(
+    out = _sanitize_authors(
         {
             "authors": [
                 {"name": ""},          # blank name → skipped
@@ -69,7 +71,7 @@ def test_sanitize_authors_skips_malformed(server_mod):
 
 @pytest.mark.parametrize("manifest", [None, {}, {"authors": None}, {"authors": "x"}, "nope"])
 def test_sanitize_authors_absent_or_nonlist(server_mod, manifest):
-    assert server_mod._sanitize_authors(manifest) == []
+    assert _sanitize_authors(manifest) == []
 
 
 # ── song_info WS integration ────────────────────────────────────────────────
@@ -118,6 +120,9 @@ def make_client(tmp_path, monkeypatch):
         monkeypatch.setattr(server, "load_plugins", lambda *a, **kw: None)
         monkeypatch.setattr(server, "startup_scan", lambda: None)
         monkeypatch.setattr(server, "SLOPPAK_CACHE_DIR", tmp_path / "cache")
+        # ws_highway reads the cache dir through the appstate seam now.
+        import appstate as _appstate
+        monkeypatch.setattr(_appstate, "sloppak_cache_dir", tmp_path / "cache")
         return server
 
     (tmp_path / "dlc").mkdir()

tests/test_highway_ws_instrument_routing.py

@@ -96,6 +96,9 @@ def make_client(tmp_path, monkeypatch):
         monkeypatch.setattr(server, "load_plugins", lambda *a, **kw: None)
         monkeypatch.setattr(server, "startup_scan", lambda: None)
         monkeypatch.setattr(server, "SLOPPAK_CACHE_DIR", tmp_path / "cache")
+        # ws_highway reads the cache dir through the appstate seam now.
+        import appstate as _appstate
+        monkeypatch.setattr(_appstate, "sloppak_cache_dir", tmp_path / "cache")
         return server
 
     (tmp_path / "dlc").mkdir()

tests/test_highway_ws_notation.py

@@ -123,6 +123,9 @@ def make_client(tmp_path, monkeypatch):
         monkeypatch.setattr(server, "load_plugins", lambda *a, **kw: None)
         monkeypatch.setattr(server, "startup_scan", lambda: None)
         monkeypatch.setattr(server, "SLOPPAK_CACHE_DIR", tmp_path / "cache")
+        # ws_highway reads the cache dir through the appstate seam now.
+        import appstate as _appstate
+        monkeypatch.setattr(_appstate, "sloppak_cache_dir", tmp_path / "cache")
         return server
 
     (tmp_path / "dlc").mkdir()

tests/test_library_filters.py

@@ -293,6 +293,45 @@ def test_year_sort_asc_oldest_first(client, seeded):
     assert files == ["b.archive", "a.archive", "f.archive", "d.sloppak", "c.sloppak", "e.sloppak"]
 
 
+def test_difficulty_sort_pushes_unrated_to_bottom(client, server_mod):
+    """Personal difficulty (song_user_meta.user_difficulty) sorts like
+    mastery: an unrated (NULL) row must fall to the bottom in BOTH
+    directions rather than colliding with a real 1..5 rating at either
+    end."""
+    _put(server_mod, filename="easy.archive", title="Easy", artist="A",
+         arrangements=[{"index": 0, "name": "Lead", "notes": 1}])
+    _put(server_mod, filename="hard.archive", title="Hard", artist="B",
+         arrangements=[{"index": 0, "name": "Lead", "notes": 1}])
+    _put(server_mod, filename="unrated.archive", title="Unrated", artist="C",
+         arrangements=[{"index": 0, "name": "Lead", "notes": 1}])
+    server_mod.meta_db.set_song_user_meta("easy.archive", user_difficulty=1)
+    server_mod.meta_db.set_song_user_meta("hard.archive", user_difficulty=5)
+
+    asc = [s["filename"] for s in _get(client, sort="difficulty")["songs"]]
+    assert asc == ["easy.archive", "hard.archive", "unrated.archive"]
+
+    desc = [s["filename"] for s in _get(client, sort="difficulty-desc")["songs"]]
+    assert desc == ["hard.archive", "easy.archive", "unrated.archive"]
+
+
+def test_tree_view_songs_carry_user_difficulty(client, server_mod):
+    """`/api/library/artists` (the classic tree view's `query_artists`) must
+    batch-attach `user_difficulty` the same way `query_page` does for the
+    grid — otherwise the tree view's difficulty badge silently never
+    renders (song.user_difficulty stays undefined for every row)."""
+    _put(server_mod, filename="rated.archive", title="Rated", artist="A",
+         arrangements=[{"index": 0, "name": "Lead", "notes": 1}])
+    _put(server_mod, filename="unrated.archive", title="Unrated", artist="A",
+         arrangements=[{"index": 0, "name": "Lead", "notes": 1}])
+    server_mod.meta_db.set_song_user_meta("rated.archive", user_difficulty=4)
+
+    data = client.get("/api/library/artists").json()
+    songs = data["artists"][0]["albums"][0]["songs"]
+    by_filename = {s["filename"]: s for s in songs}
+    assert by_filename["rated.archive"]["user_difficulty"] == 4
+    assert by_filename["unrated.archive"]["user_difficulty"] is None
+
+
 def test_tuning_sort_down_tuned_before_up_tuned_at_same_distance(client, server_mod):
     """Within an ABS(tuning_sort_key) tier, the down-tuned variant
     must come before the up-tuned one so the order matches the chart's

tests/test_loops_concurrency.py

@@ -0,0 +1,84 @@
+"""Concurrent unnamed loop saves must get unique names.
+
+`save_loop` auto-names an unnamed loop `Loop {count+1}`. If the `COUNT(*)` runs
+outside the DB lock (as it did before the fix), two simultaneous unnamed POSTs
+read the same count and both mint the same name. A `threading.Barrier` releases
+all workers into `save_loop` at once to force that interleave.
+
+Single-user app, so this race is unlikely in practice — but the fix is one lock
+scope, and the test pins it.
+"""
+
+import threading
+
+import pytest
+
+import appstate
+from metadata_db import MetadataDB
+from routers import loops
+
+
+@pytest.fixture()
+def meta_db(tmp_path):
+    prev = appstate.meta_db
+    db = MetadataDB(tmp_path)
+    appstate.configure(meta_db=db)
+    yield db
+    db.conn.close()
+    appstate.configure(meta_db=prev)
+
+
+def test_concurrent_unnamed_saves_get_unique_names(meta_db):
+    workers = 16
+    barrier = threading.Barrier(workers)
+    names, errors = [], []
+    lock = threading.Lock()
+
+    def save():
+        try:
+            barrier.wait()                       # release all at once
+            r = loops.save_loop({"filename": "song.feedpak", "start": 0.0, "end": 1.0})
+            with lock:
+                names.append(r["name"])
+        except Exception as e:                   # noqa: BLE001 — surface any thread error
+            with lock:
+                errors.append(e)
+
+    threads = [threading.Thread(target=save) for _ in range(workers)]
+    for t in threads:
+        t.start()
+    for t in threads:
+        t.join()
+
+    assert not errors, errors
+    assert len(names) == workers
+    # The load-bearing assertion: no two auto-named loops collide.
+    assert len(set(names)) == workers, f"duplicate loop names: {sorted(names)}"
+    # And the DB agrees — every insert landed.
+    stored = meta_db.conn.execute(
+        "SELECT COUNT(*) FROM loops WHERE filename = ?", ("song.feedpak",)
+    ).fetchone()[0]
+    assert stored == workers
+
+
+def test_list_and_save_do_not_error_under_interleave(meta_db):
+    """A read overlapping writes must not raise (shared connection, one lock)."""
+    stop = threading.Event()
+    errors = []
+
+    def reader():
+        while not stop.is_set():
+            try:
+                loops.list_loops("song.feedpak")
+            except Exception as e:               # noqa: BLE001
+                errors.append(e)
+
+    r = threading.Thread(target=reader)
+    r.start()
+    try:
+        for i in range(40):
+            loops.save_loop({"filename": "song.feedpak", "name": f"n{i}", "start": 0.0, "end": 1.0})
+    finally:
+        stop.set()
+        r.join()
+    assert not errors, errors

tests/test_midi_import_drums.py

@@ -185,18 +185,18 @@ def test_unmapped_drum_note_skipped(tmp_path):
 
 def test_unmapped_drum_note_reported_via_out_unmapped(tmp_path):
     """Opting in via out_unmapped records the dropped MIDI notes (count +
-    times) so a caller can surface a warning / mapping UI."""
+    times + velocities) so a caller can surface a warning / mapping UI."""
     mid = mido.MidiFile(type=1, ticks_per_beat=480)
     track = mido.MidiTrack()
     mid.tracks.append(track)
     track.append(mido.MetaMessage("set_tempo", tempo=500000, time=0))
-    track.append(mido.Message("note_on",  channel=9, note=56, velocity=100, time=0))    # cowbell — drop
+    track.append(mido.Message("note_on",  channel=9, note=56, velocity=88,  time=0))    # cowbell — drop
     track.append(mido.Message("note_off", channel=9, note=56, velocity=0,   time=240))
     track.append(mido.Message("note_on",  channel=9, note=36, velocity=100, time=0))    # kick — keep
     track.append(mido.Message("note_off", channel=9, note=36, velocity=0,   time=240))
-    track.append(mido.Message("note_on",  channel=9, note=54, velocity=100, time=0))    # tambourine — drop
+    track.append(mido.Message("note_on",  channel=9, note=54, velocity=25,  time=0))    # tambourine — drop
     track.append(mido.Message("note_off", channel=9, note=54, velocity=0,   time=240))
-    track.append(mido.Message("note_on",  channel=9, note=56, velocity=100, time=0))    # cowbell again — drop
+    track.append(mido.Message("note_on",  channel=9, note=56, velocity=44,  time=0))    # cowbell again — drop
     track.append(mido.Message("note_off", channel=9, note=56, velocity=0,   time=240))
 
     unmapped: dict[int, dict] = {}
@@ -209,6 +209,10 @@ def test_unmapped_drum_note_reported_via_out_unmapped(tmp_path):
     # Each unmapped MIDI carries the times at which it fired (rounded 3 dp).
     assert all(isinstance(t, float) for t in unmapped[56]["times"])
     assert len(unmapped[56]["times"]) == 2
+    # Velocities ride index-aligned with times — the mapping UI can carry
+    # the source dynamics through instead of flattening to a default.
+    assert unmapped[56]["velocities"] == [88, 44]
+    assert unmapped[54]["velocities"] == [25]
 
 
 def test_non_channel9_events_ignored(tmp_path):

tests/test_packaging.py

@@ -0,0 +1,112 @@
+"""Guard: every first-party module `server.py` imports must be one the packagers copy.
+
+feedback-desktop's `scripts/bundle-slopsmith.sh` copies a **hardcoded list** from
+core into the app bundle — `server.py`, `VERSION`, `lib/`, `data/`, `static/`,
+`plugins/__init__.py`. A new root-level module (say `appstate.py`) ships fine in
+Docker, imports fine under pytest, and is then *silently dropped* from the
+packaged desktop app, which dies at startup with:
+
+    File ".../Resources/slopsmith/server.py", line 71, in <module>
+        import appstate
+    ModuleNotFoundError: No module named 'appstate'
+
+That shipped once. This test is why it can't ship twice: it walks `server.py`'s
+module-level imports, keeps the ones that resolve inside this repo, and asserts
+each lives under a directory every packaging path already copies wholesale.
+
+If you add a first-party module for `server.py`, put it in `lib/` — the one core
+directory the Dockerfile (`COPY lib/`), `docker-compose.yml`, and the desktop
+bundler (`cp -r lib`) all copy, and that all three put on `sys.path`. If you
+genuinely need it at the repo root, you must also teach `bundle-slopsmith.sh`,
+the `Dockerfile`, `.dockerignore`, and `docker-compose.yml` about it — and then
+update `BUNDLED_ROOTS` below.
+"""
+
+import ast
+import importlib.util
+import pathlib
+
+import pytest
+
+REPO_ROOT = pathlib.Path(__file__).resolve().parent.parent
+
+# Directories every packaging path copies wholesale, plus the files copied by name.
+BUNDLED_ROOTS = ("lib", "plugins", "data", "static")
+BUNDLED_FILES = ("server.py", "main.py")
+
+
+def _server_toplevel_imports():
+    """Module names imported at `server.py`'s top level (not inside a function)."""
+    tree = ast.parse((REPO_ROOT / "server.py").read_text())
+    names = set()
+    for node in tree.body:                      # top level only — lazy imports are fine
+        if isinstance(node, ast.Import):
+            names.update(a.name.split(".")[0] for a in node.names)
+        elif isinstance(node, ast.ImportFrom) and node.level == 0 and node.module:
+            names.add(node.module.split(".")[0])
+    return sorted(names)
+
+
+# `spec.origin` is not always a path: built-in and frozen stdlib modules use
+# these sentinels. `Path("frozen").resolve()` would land inside the repo and
+# report `os` as first-party — so filter them before touching the filesystem.
+_NON_PATH_ORIGINS = {"built-in", "frozen", "namespace"}
+
+
+def _first_party_origin(name):
+    """Path of `name` if it resolves inside this repo, else None (stdlib/site-package)."""
+    try:
+        spec = importlib.util.find_spec(name)
+    except (ImportError, ValueError):
+        return None
+    if spec is None:
+        return None
+
+    if spec.origin and spec.origin not in _NON_PATH_ORIGINS:
+        origin = pathlib.Path(spec.origin)
+    else:
+        # Namespace/frozen: fall back to the first search location, if any.
+        locations = list(getattr(spec, "submodule_search_locations", None) or [])
+        if not locations:
+            return None
+        origin = pathlib.Path(locations[0])
+
+    if not origin.is_absolute():
+        return None                              # a sentinel, not a real path
+    origin = origin.resolve()
+    try:
+        origin.relative_to(REPO_ROOT)
+    except ValueError:
+        return None                              # outside the repo → a dependency
+    return origin
+
+
+@pytest.mark.parametrize("name", _server_toplevel_imports())
+def test_server_import_is_bundled(name):
+    origin = _first_party_origin(name)
+    if origin is None:
+        return                                   # stdlib or an installed dependency
+
+    rel = origin.relative_to(REPO_ROOT)
+    if rel.as_posix() in BUNDLED_FILES or rel.parts[0] in BUNDLED_ROOTS:
+        return
+
+    raise AssertionError(
+        f"server.py imports `{name}` from {rel}, which no packager copies.\n"
+        f"The desktop bundler (scripts/bundle-slopsmith.sh) copies only "
+        f"{BUNDLED_FILES} and {BUNDLED_ROOTS}/, so the packaged app would die "
+        f"at startup with ModuleNotFoundError: No module named '{name}'.\n"
+        f"Move it under lib/, or teach bundle-slopsmith.sh + Dockerfile + "
+        f".dockerignore + docker-compose.yml about it and update BUNDLED_ROOTS."
+    )
+
+
+def test_the_seam_and_routers_live_under_lib():
+    """Pin the two that already caused a shipped break."""
+    for name in ("appstate", "routers"):
+        origin = _first_party_origin(name)
+        assert origin is not None, f"{name} does not resolve inside the repo"
+        assert origin.relative_to(REPO_ROOT).parts[0] == "lib", (
+            f"{name} resolved to {origin.relative_to(REPO_ROOT)}; it must live "
+            f"under lib/ or the packaged desktop app will not ship it"
+        )

tests/test_playlist_cover_errors.py

@@ -0,0 +1,107 @@
+"""Playlist cover upload: client vs server errors, no temp litter, no leak.
+
+The pre-split handler caught decode AND persistence failures in one `except`,
+returned 400 for both, and echoed the exception (`Invalid image: {e}`) — so a
+disk/permission failure was mislabeled as a client error and could leak a
+filesystem path. These pin the split.
+"""
+
+import base64
+import io
+
+import pytest
+from fastapi.testclient import TestClient
+from PIL import Image
+
+import appstate
+from metadata_db import MetadataDB
+from routers import playlists
+
+
+@pytest.fixture()
+def client(tmp_path):
+    prev = (appstate.meta_db, appstate.config_dir)
+    db = MetadataDB(tmp_path)
+    appstate.configure(meta_db=db, config_dir=tmp_path)
+    app_ = __import__("fastapi").FastAPI()
+    app_.include_router(playlists.router)
+    try:
+        yield TestClient(app_), tmp_path
+    finally:
+        db.conn.close()
+        appstate.configure(meta_db=prev[0], config_dir=prev[1])
+
+
+def _png_b64():
+    buf = io.BytesIO()
+    Image.new("RGB", (8, 8), (10, 20, 30)).save(buf, "PNG")
+    return base64.b64encode(buf.getvalue()).decode()
+
+
+def _make_playlist(client):
+    return client.post("/api/playlists", json={"name": "P"}).json()["id"]
+
+
+def test_valid_cover_saves_and_leaves_no_temp(client):
+    c, tmp_path = client
+    pid = _make_playlist(c)
+    r = c.post(f"/api/playlists/{pid}/cover", json={"image": _png_b64()})
+    assert r.status_code == 200
+    cover_dir = tmp_path / "playlist_covers"
+    assert (cover_dir / f"{pid}.png").exists()
+    # The atomic-publish temp file must not linger.
+    assert not list(cover_dir.glob("*.tmp"))
+
+
+def test_undecodable_image_is_a_400_without_leaking(client):
+    c, _ = client
+    pid = _make_playlist(c)
+    # valid base64, not a valid image
+    r = c.post(f"/api/playlists/{pid}/cover", json={"image": base64.b64encode(b"not an image").decode()})
+    assert r.status_code == 400
+    body = r.json()["error"]
+    assert body == "Invalid image"          # generic — no exception detail echoed
+    assert "playlist_covers" not in body    # no filesystem path leak
+
+
+def test_save_failure_is_a_500_not_a_400(client, monkeypatch):
+    """A persistence failure (here: Image.save raising) must be a logged 500,
+    not a 400 — the whole point of the decode/persist split. Negative-checks
+    against the pre-fix behavior, which returned 400 for exactly this."""
+    c, tmp_path = client
+    pid = _make_playlist(c)
+    payload = _png_b64()                     # build BEFORE patching save
+
+    def boom(self, fp, *a, **k):
+        raise OSError("disk full")
+
+    monkeypatch.setattr(Image.Image, "save", boom)
+    r = c.post(f"/api/playlists/{pid}/cover", json={"image": payload})
+
+    assert r.status_code == 500
+    assert "disk full" not in r.json()["error"]           # no internal detail
+    assert not list((tmp_path / "playlist_covers").glob("*.tmp"))  # temp cleaned up
+
+
+def test_temp_creation_failure_is_a_500(client, monkeypatch):
+    """mkstemp raising (unwritable dir / full disk) must hit the same logged 500
+    path as a save failure, not escape as an unhandled server error."""
+    import tempfile as _tempfile
+
+    c, _ = client
+    pid = _make_playlist(c)
+    payload = _png_b64()
+
+    def boom(*a, **k):
+        raise OSError("read-only file system")
+
+    monkeypatch.setattr(_tempfile, "mkstemp", boom)
+    r = c.post(f"/api/playlists/{pid}/cover", json={"image": payload})
+    assert r.status_code == 500
+    assert "read-only" not in r.json()["error"]
+
+
+def test_upload_to_missing_playlist_is_404(client):
+    c, _ = client
+    r = c.post("/api/playlists/9999/cover", json={"image": _png_b64()})
+    assert r.status_code == 404

tests/test_playlists_api.py

@@ -6,6 +6,10 @@ import sys
 import pytest
 from fastapi.testclient import TestClient
 
+# Moved to routers/playlists in R3; reads appstate.config_dir, which the
+# `server` fixture configures via CONFIG_DIR before this is called.
+from routers.playlists import _playlist_cover_path
+
 
 @pytest.fixture()
 def server(tmp_path, monkeypatch, isolate_logging):
@@ -168,6 +172,6 @@ def test_cover_rejects_non_string_image_with_400_not_500(client):
 def test_deleting_playlist_removes_custom_cover(client, server):
     pid = client.post("/api/playlists", json={"name": "Doomed"}).json()["id"]
     client.post(f"/api/playlists/{pid}/cover", json={"image": _png_b64()})
-    assert server._playlist_cover_path(pid).exists()
+    assert _playlist_cover_path(pid).exists()
     client.delete(f"/api/playlists/{pid}")
-    assert not server._playlist_cover_path(pid).exists()
+    assert not _playlist_cover_path(pid).exists()

tests/test_plugin_src_route.py

@@ -0,0 +1,140 @@
+"""Tests for the plugin `src/` module-serving route and the live-edit cache
+contract added in R0 (module-migration rails).
+
+Covers:
+  * GET /api/plugins/{id}/src/{path} serves a plugin's ES-module source tree
+    with the right Content-Type, including nested paths.
+  * Path containment: `..`, absolute, and NUL are rejected (404) — the same
+    `safe_join` guard the assets/ route uses.
+  * The live-edit cache contract: no-cache + a weak ETag, a bodyless 304 on
+    matching If-None-Match, and no stale 304 after an in-place edit.
+  * screen.js and assets/ now also emit an ETag and honor If-None-Match
+    (previously screen.js sent no headers and assets/ never returned 304).
+
+The routes read the module-global `plugins.LOADED_PLUGINS`, so each test
+registers a fake ready plugin directly (save/restore that global) and drives
+`register_plugin_api` on a fresh FastAPI app — no full server import needed.
+"""
+
+import pytest
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+
+import plugins
+
+
+PLUGIN_ID = "srctest"
+
+
+@pytest.fixture()
+def client(tmp_path):
+    """A TestClient with `register_plugin_api` wired and a single fake ready
+    plugin whose dir (`tmp_path`) holds a src/ tree, an asset, and a screen.js.
+    Restores LOADED_PLUGINS afterward."""
+    (tmp_path / "src").mkdir()
+    (tmp_path / "src" / "main.js").write_text("import './util/x.js';\nexport const boot = 1;\n")
+    (tmp_path / "src" / "util").mkdir()
+    (tmp_path / "src" / "util" / "x.js").write_text("export const x = 42;\n")
+    (tmp_path / "src" / "theme.css").write_text(".a{color:red}\n")
+    (tmp_path / "assets").mkdir()
+    (tmp_path / "assets" / "worklet.js").write_text("// worklet\n")
+    (tmp_path / "screen.js").write_text("import './src/main.js';\n")
+
+    saved = list(plugins.LOADED_PLUGINS)
+    plugins.LOADED_PLUGINS.clear()
+    plugins.LOADED_PLUGINS.append({
+        "id": PLUGIN_ID,
+        "status": "ready",
+        "_dir": tmp_path,
+        "_manifest": {"script": "screen.js", "scriptType": "module"},
+    })
+    app = FastAPI()
+    plugins.register_plugin_api(app)
+    c = TestClient(app, raise_server_exceptions=True)
+    try:
+        yield c, tmp_path
+    finally:
+        c.close()
+        plugins.LOADED_PLUGINS.clear()
+        plugins.LOADED_PLUGINS.extend(saved)
+
+
+def test_src_file_served_with_js_media_type(client):
+    c, _ = client
+    r = c.get(f"/api/plugins/{PLUGIN_ID}/src/main.js")
+    assert r.status_code == 200
+    # Either application/javascript or text/javascript is a valid module-script
+    # MIME (guess_type returns text/javascript on newer platforms); browsers
+    # accept both for <script type=module>.
+    assert "javascript" in r.headers["content-type"]
+    assert "export const boot" in r.text
+    assert r.headers["cache-control"] == "no-cache"
+    assert r.headers.get("etag")
+
+
+def test_src_nested_path_and_css_media_type(client):
+    c, _ = client
+    assert c.get(f"/api/plugins/{PLUGIN_ID}/src/util/x.js").status_code == 200
+    r = c.get(f"/api/plugins/{PLUGIN_ID}/src/theme.css")
+    assert r.status_code == 200
+    assert r.headers["content-type"].startswith("text/css")
+
+
+@pytest.mark.parametrize("bad", [
+    "..%2f..%2fplugin.json",     # escape the src/ dir
+    "..%2f..%2f..%2fetc%2fpasswd",
+    "%2fetc%2fpasswd",           # absolute
+    "util%2f..%2f..%2fscreen.js",
+])
+def test_src_traversal_rejected(client, bad):
+    c, _ = client
+    assert c.get(f"/api/plugins/{PLUGIN_ID}/src/{bad}").status_code == 404
+
+
+def test_src_missing_is_404(client):
+    c, _ = client
+    assert c.get(f"/api/plugins/{PLUGIN_ID}/src/nope.js").status_code == 404
+
+
+def test_src_conditional_304(client):
+    c, _ = client
+    r1 = c.get(f"/api/plugins/{PLUGIN_ID}/src/main.js")
+    etag = r1.headers["etag"]
+    r2 = c.get(f"/api/plugins/{PLUGIN_ID}/src/main.js", headers={"If-None-Match": etag})
+    assert r2.status_code == 304
+    assert r2.content == b""
+
+
+def test_src_no_stale_304_after_edit(client):
+    c, root = client
+    etag = c.get(f"/api/plugins/{PLUGIN_ID}/src/main.js").headers["etag"]
+    (root / "src" / "main.js").write_text("export const boot = 2;  // edited, longer body\n")
+    r = c.get(f"/api/plugins/{PLUGIN_ID}/src/main.js", headers={"If-None-Match": etag})
+    assert r.status_code == 200
+    assert "boot = 2" in r.text
+    assert r.headers["etag"] != etag
+
+
+def test_screen_js_now_conditional(client):
+    c, _ = client
+    r1 = c.get(f"/api/plugins/{PLUGIN_ID}/screen.js")
+    assert r1.status_code == 200
+    assert r1.headers["cache-control"] == "no-cache"
+    etag = r1.headers["etag"]
+    r2 = c.get(f"/api/plugins/{PLUGIN_ID}/screen.js", headers={"If-None-Match": etag})
+    assert r2.status_code == 304
+
+
+def test_asset_now_conditional(client):
+    c, _ = client
+    r1 = c.get(f"/api/plugins/{PLUGIN_ID}/assets/worklet.js")
+    assert r1.status_code == 200
+    etag = r1.headers["etag"]
+    r2 = c.get(f"/api/plugins/{PLUGIN_ID}/assets/worklet.js", headers={"If-None-Match": etag})
+    assert r2.status_code == 304
+
+
+def test_unready_plugin_src_is_404(client):
+    c, _ = client
+    plugins.LOADED_PLUGINS[0]["status"] = "installing"
+    assert c.get(f"/api/plugins/{PLUGIN_ID}/src/main.js").status_code == 404

tests/test_settings_api.py

@@ -50,7 +50,7 @@ def client(tmp_path, monkeypatch):
     # Point CONFIG_DIR at a per-test temp path BEFORE server's
     # import-time side effects run. server.py reads CONFIG_DIR from the
     # environment at module load (line 35) and immediately constructs
-    # `meta_db = MetadataDB()` at module level, which calls
+    # `meta_db = MetadataDB(CONFIG_DIR)` at module level, which calls
     # CONFIG_DIR.mkdir(...) and opens a sqlite file — a plain
     # post-import monkeypatch on server.CONFIG_DIR wouldn't catch those
     # side effects, and the real user config dir would get written to.

tests/test_settings_export_library_db.py

@@ -22,6 +22,11 @@ from pathlib import Path
 import pytest
 from fastapi.testclient import TestClient
 
+# The startup DB swap lives with the DB layer it guards, not with server.py.
+# metadata_db reads no environment at import, so a plain module import is safe
+# alongside the env-patched `server_mod` fixture below.
+from metadata_db import _apply_pending_db_restore
+
 
 @pytest.fixture()
 def server_mod(tmp_path, monkeypatch):
@@ -219,7 +224,7 @@ def test_apply_pending_db_restore_swaps_and_clears_sidecars(server_mod, tmp_path
     (tmp_path / "web_library.db-shm").write_bytes(b"OLD-SHM")
     (tmp_path / "web_library.db.restore").write_bytes(new_db)
 
-    server_mod._apply_pending_db_restore(tmp_path)
+    _apply_pending_db_restore(tmp_path)
 
     assert main.read_bytes() == new_db                  # swapped in
     assert not (tmp_path / "web_library.db.restore").exists()
@@ -234,7 +239,7 @@ def test_apply_pending_db_restore_discards_corrupt_keeps_live(server_mod, tmp_pa
     main.write_bytes(b"LIVE-GOOD-DB")
     (tmp_path / "web_library.db.restore").write_bytes(b"SQLite format 3\x00" + b"\xff" * 64)
 
-    server_mod._apply_pending_db_restore(tmp_path)
+    _apply_pending_db_restore(tmp_path)
 
     assert main.read_bytes() == b"LIVE-GOOD-DB"          # live DB preserved
     assert not (tmp_path / "web_library.db.restore").exists()  # bad restore dropped
@@ -242,7 +247,7 @@ def test_apply_pending_db_restore_discards_corrupt_keeps_live(server_mod, tmp_pa
 
 def test_apply_pending_db_restore_noop_without_staging(server_mod, tmp_path):
     (tmp_path / "web_library.db").write_bytes(b"LIVE")
-    server_mod._apply_pending_db_restore(tmp_path)        # nothing staged
+    _apply_pending_db_restore(tmp_path)        # nothing staged
     assert (tmp_path / "web_library.db").read_bytes() == b"LIVE"
 
 
@@ -266,7 +271,7 @@ def test_full_db_backup_restore_round_trip(client, server_mod, tmp_path):
     # Simulate a restart: close the live conn, apply the staged restore,
     # reopen — the song is back.
     server_mod.meta_db.conn.close()
-    server_mod._apply_pending_db_restore(tmp_path)
+    _apply_pending_db_restore(tmp_path)
     conn = sqlite3.connect(str(tmp_path / "web_library.db"))
     try:
         rows = conn.execute(

tests/test_tunings.py

@@ -249,3 +249,30 @@ def test_flat_string_count_patch_resets_incompatible_named_tuning():
     patched = apply_flat_instrument_patch_to_profiles(settings, {"string_count": 7})
     assert patched["string_count"] == 7
     assert patched["tuning"] == "Standard"
+
+
+# ── freqs_to_midis (the /api/tunings tuningMidis inverse) ────────────────────
+
+def test_freqs_to_midis_round_trips_every_builtin_at_440():
+    from tunings import freqs_to_midis
+    for key, presets in TUNING_PRESET_MIDIS.items():
+        for name, midis in presets.items():
+            assert freqs_to_midis(open_midis_to_freqs(midis)) == midis, f"{key}/{name}"
+
+
+def test_freqs_to_midis_round_trips_at_nonstandard_reference():
+    # The consumer footgun this exists to kill: frequencies served at a 432/450
+    # reference must recover the SAME integer midis when inverted at that
+    # reference (client-side log2-at-440 reconstruction drifts here).
+    from tunings import freqs_to_midis
+    for ref in (430.0, 432.0, 444.0, 450.0):
+        for midis in (TUNING_PRESET_MIDIS["guitar-8"]["Standard"], TUNING_PRESET_MIDIS["bass-5"]["Standard"]):
+            freqs = open_midis_to_freqs(midis, ref)
+            assert freqs_to_midis(freqs, ref) == midis, f"ref={ref}"
+
+
+def test_freqs_to_midis_rejects_garbage():
+    from tunings import freqs_to_midis
+    assert freqs_to_midis([82.41, 0]) is None          # non-positive
+    assert freqs_to_midis([82.41, "x"]) is None        # non-numeric
+    assert freqs_to_midis([]) == []                    # vacuously fine

tests/test_ws_highway_disconnect.py

@@ -0,0 +1,110 @@
+"""A client that disconnects mid-stream is routine, not a logged error.
+
+The highway WS streams ~15 message batches before its keep-alive loop. A
+disconnect during that streaming used to fall through to the blanket
+`except Exception` and log `highway_ws unhandled error`. The dedicated
+`except WebSocketDisconnect: return` makes it quiet.
+"""
+
+import asyncio
+import importlib
+import json
+import logging
+import sys
+
+import pytest
+import yaml
+from fastapi import WebSocketDisconnect
+
+
+def _write_sloppak(dlc_root):
+    pak = dlc_root / "disc.sloppak"
+    pak.mkdir(parents=True)
+    (pak / "arrangements").mkdir()
+    (pak / "arrangements" / "lead.json").write_text(json.dumps({
+        "notes": [], "chords": [], "anchors": [], "handshapes": [],
+        "templates": [], "beats": [{"time": 0.0, "measure": 1}],
+        "sections": [{"name": "intro", "number": 1, "time": 0.0}],
+    }))
+    (pak / "manifest.yaml").write_text(yaml.safe_dump({
+        "title": "Disc", "artist": "T", "album": "", "year": 2026, "duration": 10.0,
+        "arrangements": [{"id": "lead", "name": "Lead", "file": "arrangements/lead.json"}],
+        "stems": [],
+    }, sort_keys=False))
+    return pak
+
+
+class _DisconnectingWS:
+    """Accepts, then raises WebSocketDisconnect on the first streamed send —
+    i.e. a client that drops mid-stream."""
+    def __init__(self):
+        self.sends = 0
+
+    async def accept(self):
+        pass
+
+    async def send_json(self, data):
+        self.sends += 1
+        # Raise only on the FIRST send. If the handler wrongly kept streaming
+        # after catching the disconnect, later sends would succeed and `sends`
+        # would climb past 1 — the exactly-one assertion catches that.
+        if self.sends == 1:
+            raise WebSocketDisconnect(code=1001)
+
+    async def receive_text(self):
+        raise WebSocketDisconnect(code=1001)
+
+    async def close(self):
+        pass
+
+
+@pytest.fixture()
+def server(tmp_path, monkeypatch):
+    (tmp_path / "dlc").mkdir()
+    monkeypatch.setenv("CONFIG_DIR", str(tmp_path / "config"))
+    monkeypatch.setenv("DLC_DIR", str(tmp_path / "dlc"))
+    monkeypatch.setenv("FEEDBACK_SKIP_STARTUP_TASKS", "1")
+    sys.modules.pop("server", None)
+    mod = importlib.import_module("server")
+    yield mod, tmp_path / "dlc"
+    conn = getattr(getattr(mod, "meta_db", None), "conn", None)
+    if conn is not None:
+        getattr(mod, "_join_background_db_threads", lambda: None)()
+        conn.close()
+    sys.modules.pop("server", None)
+
+
+class _Capture(logging.Handler):
+    def __init__(self):
+        super().__init__()
+        self.messages = []
+
+    def emit(self, record):
+        self.messages.append(record.getMessage())
+
+
+def test_midstream_disconnect_is_not_logged_as_error(server):
+    """The first streamed send (`loading`) raises WebSocketDisconnect; the
+    handler must return quietly, not log `highway_ws unhandled error`.
+
+    A raw handler on `feedBack.server` is used rather than pytest's `caplog`
+    because `configure_logging()` (run at server import) reroutes that logger
+    through the structlog pipeline, which caplog's fixture doesn't observe.
+    """
+    _server, dlc = server
+    _write_sloppak(dlc)
+    from routers.ws_highway import highway_ws
+
+    cap = _Capture()
+    cap.setLevel(logging.ERROR)
+    lg = logging.getLogger("feedBack.server")
+    lg.addHandler(cap)
+    try:
+        ws = _DisconnectingWS()
+        asyncio.run(highway_ws(ws, "disc.sloppak", arrangement=0))  # must not raise
+    finally:
+        lg.removeHandler(cap)
+
+    assert ws.sends == 1, f"handler kept streaming after the disconnect ({ws.sends} sends)"
+    unhandled = [m for m in cap.messages if "highway_ws unhandled error" in m]
+    assert not unhandled, f"disconnect logged as unhandled error: {unhandled}"