feat(core): host per-instrument workingTuning capability + read-API/event (working-tuning PR 1) (#658)

* feat(core): host per-instrument workingTuning capability + read-API/event (working-tuning PR 1)

Introduce window.feedBack.workingTuning — the live, host-authoritative current
instrument tuning (offsets + string-count + reference pitch + assumed/verified
provenance), distinct from any one song's tuning and from a soft opt-in default.
It's the single source of truth the highway, library, and plugins (tuner,
Virtuoso, minigames) will read so a retune or instrument swap is reflected
app-wide instead of being re-derived per surface.

PER-INSTRUMENT: state is a map keyed by `${instrument}-${stringCount}` (e.g.
guitar-6 / bass-4, the selector's key) — your guitar's tuning and your bass's are
kept separately; get() returns the selected instrument's, and switching the
selector surfaces that instrument's own remembered tuning. You only ever deal
with the one you've picked.

Modeled on the shipped `tuning` capability + the `feedBack.theme` read-API:
synchronous get(instrument?), set(state,{provenance,instrument}) mutator,
setCurrentInstrument(), resetToDefault(), and a `working-tuning-changed` event
that fires on change and once on hydration (carrying which instrument changed).
In-memory, seeded from /api/settings, reset-on-restart. Registered as a separate
`working-tuning` exclusive-owner capability (tuner = sole writer, others read).

Foundation only — pure plumbing, nothing writes to it yet and no behavior
changes. The tuner becomes the writer (and the gate's E->C# asymmetry is fixed)
in a later PR.

Frontend-only: new static/capabilities/working-tuning.js, loaded from
static/index.html + static/v3/index.html. Per-instrument state machine verified
by a stubbed node harness (separate guitar/bass slots, selector switch, isolated
writes, verified stamp, reset, defensive copies, capability registration).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QbexxfTt8q2tAn436MqGWF

* fix(working-tuning): resolve review P1/P2s + add behavioral test harness

Addresses the manual + Codex review of PR 1 (working-tuning foundation).

P1 — named tunings were dropped by the boot seed: /api/settings.tuning may be a
name ("Drop D") OR an offsets list, but the seed only handled the list and stored
offsets:null for names. The seed now resolves a name to per-string semitone offsets
via /api/tunings (ratio vs Standard; reference pitch cancels).

P1 — async seed could clobber state a consumer had already written: _seedFromSettings
resolves after boot and used to overwrite _currentKey/_byInstrument unconditionally.
It now bails when state was already _touched (and re-checks after the /api/tunings
leg), so an explicit set()/setCurrentInstrument()/resetToDefault() before hydration
wins. Hydration still fires.

P1/P2 — shallow copy leaked live nested arrays: get() and set() now clone offsets and
verifiedStrings on both ingress and egress, honouring the "readers can't mutate live
state" contract.

P2 — provenance/verification state machine made coherent by construction:
verified <=> verifiedStrings is an array AND verifiedAt is a finite number. A tuning
change invalidates prior verification unless a fresh bundle is supplied; a "verified"
claim with no strings or a null/absent timestamp is repaired (assumed / stamped now).

P2 — bare-instrument writes targeted a hard-coded default string count: _keyOfResolved()
resolves an omitted string count against the current selection (same instrument), so
set({instrument:'bass'}) / set({stringCount:5}) hit the selected bass-5, not bass-4.

Test — adds tests/js/working_tuning.test.js (the harness the PR described but did not
commit): 11 behavioral cases over a stubbed window — registration, per-instrument
isolation + selector switch, defensive copies, the verification invariant, bare-key
routing, named + offsets-list seeding, and the boot-race guard. Full tests/js suite:
no new failures (the 12 pre-existing branch failures are unrelated).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
Co-authored-by: byrongamatos <xasiklas@gmail.com>

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### Added
+- **Host "working tuning" — a live, app-wide record of what tuning your instrument is *actually* in right now (foundation; no behavior change yet).** Introduces `window.feedBack.workingTuning`, a host-owned, session-lived state distinct from any one song's tuning and from a soft opt-in default: the offsets + string-count + reference pitch the player's instrument is currently in, plus an `assumed`/`verified` provenance flag. It's **per-instrument** — your guitar's current tuning and your bass's are kept *separately* (keyed like the instrument selector, e.g. `guitar-6` / `bass-4`), so switching instruments surfaces that instrument's own remembered tuning and you only ever deal with the one you've selected. It exists so a retune — or an instrument swap mid-session — is reflected **everywhere** (the highway, the library/song-picker, and plugins like the tuner, Virtuoso, and the minigames) instead of being re-derived per surface or wrongly assumed from a fixed profile. Modeled on the shipped `tuning` capability + the `feedBack.theme` read-API: a **synchronous `get(instrument?)`** (returns the selected instrument's state, defaulting to the seed until known), a `set(state, {provenance, instrument})` mutator (the tuner becomes the sole writer in the next change), `setCurrentInstrument()` for the selector, `resetToDefault()`, and a `working-tuning-changed` event that fires on every change **and once on hydration** (carrying which instrument changed) so a late-mounting consumer is never stuck on stale state. State is **in-memory, seeded from `/api/settings` on boot and reset on restart** — a stale "you're in drop-A" assumption is worse than re-asking. Registered as a separate `working-tuning` **exclusive-owner** capability (tuner = writer, the rest = requesters). This is the foundation (plumbing only — nothing writes to it yet) of the working-tuning series, which fixes the tuner gate only ever prompting *away from* a fixed "home" tuning (never back) and makes the current tuning a first-class signal the whole app shares. Offsets use the same per-string semitone vocabulary as song tunings, so fully custom/extended tunings (e.g. a drop-A 8-string) are first-class. Frontend-only: new `static/capabilities/working-tuning.js`, loaded from `static/index.html` + `static/v3/index.html`.
 - **The v3 Songs grid is now DOM-virtualized — card-node count stays bounded no matter how big the library is or how far you scroll.** The grid used to append every scrolled page and never let go, so a 2000-song library grew the DOM from 24 → 624 → 2001 card nodes as you scrolled (layout/memory cost scaling with depth). It now renders only the **visible window** of cards (± a small overscan); a sizer element sized to the whole library (`ceil(total/cols) × rowH`) gives the scrollbar its full geometry while the grid is absolutely positioned to the first visible row. `state.songs` is a sparse, absolutely-indexed store fetched a page at a time on demand — using the stage-1 **keyset cursor** for contiguous forward scroll (O(page)) and falling back to `OFFSET page=` for jumps/restore/non-keyset providers (collections, remote). Verified bounded (~60 nodes for a 2001-song library while the count still reads "2001 songs"). The **A–Z rail now seeks directly**: `sort_letters` gives a letter's first-row index (cumulative of prior buckets), converted to a scrollTop in O(1) — no more paging through every intervening row (a bounded forward scan covers the rare legacy provider without `sort_letters`). Select-mode selections, accuracy badges, the ⋮ card menu, plugin card actions, scroll-restore (now scrollTop-based, since geometry is stable), and the tree/folder views all survive cards leaving and re-entering the DOM. Plugins that decorate cards get a stable `window.v3Songs.visibleCards()` accessor + a `v3:library-window-rendered` event instead of assuming every card is present (the highway-stutter lesson). Stage 2 of the virtualized-grid project (got-feedback/feedBack#636 item 3), building on the stage-1 keyset data layer below. Frontend-only: `static/v3/songs.js`, `static/v3/v3.css`. Tests: `tests/browser/v3-grid-virtualization.spec.ts` (bounded-DOM invariant across a 2001-song scroll + direct rail jump), updated `tests/js/v3_az_rail.test.js` + `tests/js/v3_songs_scroll.test.js`.
 - **Keyset (cursor) pagination for the library grid — the data layer for an upcoming virtualized grid, and a latent paging bug fixed along the way.** Every library sort now carries a unique `filename` tiebreak, making the order **total** — which fixes a latent bug where rows sharing a sort key (e.g. two songs by the same artist) could be skipped or duplicated across `OFFSET` pages. `GET /api/library` gains an opaque `after` cursor + a `next_cursor` in the response: passing the cursor back fetches the next page with a **WHERE-seek** instead of `OFFSET`, so deep paging is O(page) regardless of depth. The seek is NULL-aware and exactly `OFFSET`-equivalent (verified across artist/title/recent, ascending + descending, including the legacy `dir=desc` shape and NULL sort keys); unknown/compound sorts and bad cursors fall back to `OFFSET`, and only the local provider is handed a cursor (collections/remote page by `OFFSET`). New composite `(artist NOCASE, filename)` / `(title NOCASE, filename)` / `(mtime, filename)` indexes cover the order. This is stage 1 of the virtualized-grid project (got-feedback/feedBack#636 item 3); the DOM-recycling render window builds on it next. Tests: `tests/test_library_keyset.py` (keyset==OFFSET parity, stable tiebreak, dir=desc, NULL keys, cursor fallback).
 - **Smart collections — save a set of library filters as a live, auto-updating source.** A collection is a saved `/api/library` query (e.g. "Drop-D tunings", "sloppak only", "recently added") that stays live: it's registered as a **library provider**, so it shows up in the v3 Songs source picker and inherits the whole grid UI — paging, stats, the A–Z rail, art — for free, with **no new screen**. Storage reuses the playlist subsystem (a `playlists.rules` JSON blob = a smart collection; membership is the live filter result, not stored songs, and collections are excluded from the manual-playlist list + read-only to playlist mutations). New `GET`/`POST`/`PUT`/`DELETE /api/collections`; a per-collection `SmartCollectionProvider` delegates `query_page`/`query_stats`/`query_artists` to the local DB with the stored rules applied; providers are re-registered from a boot scan so collections survive a restart. Rules mirror the raw `/api/library` query params (unknown keys dropped, never 500). Frontend: a "＋ Save as collection" action in the v3 filter drawer (shown when filters are active) names the current filter set and switches to it. The charrette's "the homelab primitive FeedBack was missing" pick (got-feedback/feedBack#636 item 2); richer rule fields (accuracy, genre, difficulty) follow as the metadata work lands. Tests: `tests/test_collections_api.py`, `tests/js/v3_collections.test.js`.