refactor(server): extract the settings routes into routers/settings.py (R3)

GET/POST /api/settings, /api/settings/reset, and the two-phase atomic
export/import bundle (/api/settings/export|import) move to lib/routers/settings.py
with their exclusive helpers (the relpath allowlist validator, the atomic writer,
the library-DB snapshot + sqlite integrity gate, the config-type validator, the
bundle schema). Bodies verbatim except @app->@router and the seam reads:
meta_db->appstate.meta_db, CONFIG_DIR->appstate.config_dir,
_running_version->appstate.running_version(), and _default_settings->
appstate.default_settings (the canonical defaults builder stays in server.py —
the scan + artist-links code share it — and is injected as a new seam callable).

server.py: 5,539 -> 4,478 (-1,061).

Verified: pyflakes clean (bar the pre-existing File/safe_join/tuning_name/ET);
route table IDENTICAL (143); full pytest 2397 passed (154 settings cases incl the
export→import round-trip + library-DB snapshot/restore + relpath-allowlist SSRF/
traversal guards, retargeted onto the settings module). eslint 0.

BEHAVIORAL — needs an on-device settings export→import round-trip sign-off before
merge (do not merge on green CI alone).

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

CHANGELOG.md

@@ -27,7 +27,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### 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), `library_extras`, `wanted`, `shop`, `progression`, `profile`, `stats` (the `/api/stats/{path}` catch-all stays registered last so it can't shadow `/recent` `/best` `/top`), `version` (`/api/version`; VERSION-file lookup adjusted for the router subdir depth), `art` (the `/api/song/{f}/art*` serve/cover-search/candidates/upload/url + `/api/art/{f}/override` routes; the shared `_song_pack_art_exists`/`_art_override_paths`/`_art_safe_name` helpers stay in `server.py` for the song/delete routes and are reached through the `appstate` seam, the CAA/release transport as `enrichment.X`), and `diagnostics` (`/api/diagnostics/export|preview|hardware`; the plugins-root lookup adjusted for the router subdir depth, `_running_version` reached through the `appstate` seam, pure payload-cap helpers re-exported for the `server._diag_*` tests), and `tunings` (`/api/tunings`; the pure `config.json` reader moved to `lib/appconfig.py`, the tuning-provider registry read through the `appstate` seam so plugin-contributed tunings still merge). 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/` — 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), `library_extras`, `wanted`, `shop`, `progression`, `profile`, `stats` (the `/api/stats/{path}` catch-all stays registered last so it can't shadow `/recent` `/best` `/top`), `version` (`/api/version`; VERSION-file lookup adjusted for the router subdir depth), `art` (the `/api/song/{f}/art*` serve/cover-search/candidates/upload/url + `/api/art/{f}/override` routes; the shared `_song_pack_art_exists`/`_art_override_paths`/`_art_safe_name` helpers stay in `server.py` for the song/delete routes and are reached through the `appstate` seam, the CAA/release transport as `enrichment.X`), and `settings` (`GET`/`POST /api/settings`, `/reset`, and the two-phase atomic export/import bundle `/api/settings/export|import`; the shared `_default_settings` builder stays in `server.py` and is reached through the `appstate` seam), and `diagnostics` (`/api/diagnostics/export|preview|hardware`; the plugins-root lookup adjusted for the router subdir depth, `_running_version` reached through the `appstate` seam, pure payload-cap helpers re-exported for the `server._diag_*` tests), and `tunings` (`/api/tunings`; the pure `config.json` reader moved to `lib/appconfig.py`, the tuning-provider registry read through the `appstate` seam so plugin-contributed tunings still merge). 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

docs/size-exemptions.md

@@ -55,8 +55,8 @@ without a *signed* exemption" is unenforceable.
 ## 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`
-(5,540 — was 14,037; ratcheted by the R3 `MetadataDB` + `AudioEffectsMappingDB`
+(4,478 — was 14,037; ratcheted by the R3 `MetadataDB` + `AudioEffectsMappingDB`
-extractions and sixteen `routers/` modules (the album-art routes are now `lib/routers/art.py`); the ~930-line metadata-enrichment subsystem — MB/CAA/AcoustID transport, matcher, background worker — now lives in `lib/enrichment.py`) ·
+extractions and seventeen `routers/` modules (album-art in `lib/routers/art.py`, the settings + export/import bundle in `lib/routers/settings.py`); the ~930-line metadata-enrichment subsystem — MB/CAA/AcoustID transport, matcher, background worker — now lives in `lib/enrichment.py`) ·
 `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`

lib/appstate.py

@@ -99,6 +99,9 @@ art_cache_dir = None
 song_pack_art_exists = None
 art_override_paths = None
 art_safe_name = None
+# The canonical settings-defaults builder — stays in server.py (shared with the
+# scan/artist-links code) but the settings router calls it through the seam.
+default_settings = None
 
 _SLOTS = frozenset({
     "meta_db", "audio_effect_mappings", "tuning_providers",
@@ -107,6 +110,7 @@ _SLOTS = frozenset({
     "get_progression_content", "builtin_diagnostic_filename",
     "running_version",
     "art_cache_dir", "song_pack_art_exists", "art_override_paths", "art_safe_name",
+    "default_settings",
 })
 
 

tests/test_feedpak_extension.py

@@ -14,6 +14,7 @@ back-compat for `.sloppak` libraries or stop accepting the new `.feedpak`:
 from __future__ import annotations
 
 import importlib
+from routers import settings as settings_router
 import io
 import sys
 import zipfile
@@ -242,7 +243,7 @@ def test_settings_dlc_count_includes_both_suffixes(tmp_path, settings_server):
     (dlc / "c.FEEDPAK").write_bytes(b"")   # case-insensitive (suffix.lower())
     (dlc / "notes.txt").write_bytes(b"")   # ignored
 
-    result = settings_server.save_settings({"dlc_dir": str(dlc)})
+    result = settings_router.save_settings({"dlc_dir": str(dlc)})
 
     assert "error" not in result, result
     # save_settings joins its notices into a single ``message`` string.

tests/test_settings_api.py

@@ -10,6 +10,7 @@ shadow the config.json dlc_dir fallback.
 """
 
 import importlib
+from routers import settings as settings_router
 import json
 import sys
 
@@ -32,13 +33,13 @@ class _DirectSettingsClient:
     def get(self, path):
         if path != "/api/settings":
             raise ValueError(f"unsupported path: {path}")
-        return _DirectResponse(self._server.get_settings())
+        return _DirectResponse(settings_router.get_settings())
 
     def post(self, path, json):
         if path == "/api/settings":
-            return _DirectResponse(self._server.save_settings(json))
+            return _DirectResponse(settings_router.save_settings(json))
         if path == "/api/settings/reset":
-            return _DirectResponse(self._server.reset_settings(json))
+            return _DirectResponse(settings_router.reset_settings(json))
         raise ValueError(f"unsupported path: {path}")
 
     def close(self):
@@ -643,7 +644,7 @@ def test_achievements_enabled_persists_and_validates(api_client, tmp_path):
 
 def test_achievements_enabled_is_resettable(server_module):
     """The flag is in the resettable allow-list so a Reset clears it to default."""
-    assert "achievements_enabled" in server_module._RESETTABLE_SETTINGS_KEYS
+    assert "achievements_enabled" in settings_router._RESETTABLE_SETTINGS_KEYS
 
 
 def test_skip_startup_tasks_drives_startup_to_complete(api_client):

tests/test_settings_export.py

@@ -11,6 +11,7 @@ is exercised separately in `test_plugins.py`.
 
 import base64
 import importlib
+from routers import settings as settings_router
 import json
 import os
 import sys
@@ -478,7 +479,7 @@ def test_normalize_export_paths_consistency(server_mod, tmp_path):
         # Wraps `_validate_relpath` to assert it doesn't raise the
         # hard-failure ValueErrors. _UndeclaredFile would mean the
         # allowlist is wrong, not that the relpath shape is bad.
-        server_mod._validate_relpath(rel, cleaned, tmp_path)
+        settings_router._validate_relpath(rel, cleaned, tmp_path)
 
 
 # ── Atomic write: unique tmp + cleanup on failure ───────────────────────────
@@ -502,7 +503,7 @@ def test_atomic_write_cleans_up_tmp_on_failure(server_mod, tmp_path, monkeypatch
 
     for _ in range(2):
         with pytest.raises(OSError):
-            server_mod._atomic_write_file(target, b"payload")
+            settings_router._atomic_write_file(target, b"payload")
 
     # Both attempts cleaned up. No .tmp.import residue means the
     # mkstemp + finally-unlink pattern held even across failures.
@@ -512,7 +513,7 @@ def test_atomic_write_cleans_up_tmp_on_failure(server_mod, tmp_path, monkeypatch
 
     # Restoring real replace, the function should still work end-to-end.
     monkeypatch.setattr(server_mod.os, "replace", real_replace)
-    server_mod._atomic_write_file(target, b"payload")
+    settings_router._atomic_write_file(target, b"payload")
     assert target.read_bytes() == b"payload"
     assert list(tmp_path.glob("*.tmp.import")) == []
 
@@ -764,7 +765,7 @@ def test_atomic_write_closes_fd_when_fdopen_fails(server_mod, tmp_path, monkeypa
     monkeypatch.setattr(server_mod.os, "fdopen", boom_fdopen)
 
     with pytest.raises(OSError, match="simulated EMFILE"):
-        server_mod._atomic_write_file(target, b"payload")
+        settings_router._atomic_write_file(target, b"payload")
 
     # fd was closed (so it didn't leak), and the temp file mkstemp
     # created was removed (so it doesn't litter / lock on Windows).

tests/test_settings_export_library_db.py

@@ -15,6 +15,7 @@ this file pins the additive `core_server_files` section:
 
 import base64
 import importlib
+from routers import settings as settings_router
 import sqlite3
 import sys
 from pathlib import Path
@@ -118,7 +119,7 @@ def test_import_stages_db_restore_without_touching_live_db(client, server_mod, t
 
     payload = _valid_db_bytes(tmp_path, name="incoming.db", marker="restored")
     r = client.post("/api/settings/import", json={
-        "schema": server_mod.SETTINGS_BUNDLE_SCHEMA,
+        "schema": settings_router.SETTINGS_BUNDLE_SCHEMA,
         "server_config": {},
         "core_server_files": {
             "web_library.db": {"encoding": "base64",
@@ -143,7 +144,7 @@ def test_import_rejects_corrupt_db_with_valid_magic_header(client, server_mod, t
     # fail to open the bad restore.
     corrupt = b"SQLite format 3\x00" + b"\xff" * 200
     r = client.post("/api/settings/import", json={
-        "schema": server_mod.SETTINGS_BUNDLE_SCHEMA,
+        "schema": settings_router.SETTINGS_BUNDLE_SCHEMA,
         "server_config": {},
         "core_server_files": {
             "web_library.db": {"encoding": "base64",
@@ -158,7 +159,7 @@ def test_import_rejects_non_sqlite_db_payload(client, server_mod, tmp_path):
     # A truncated / wrong file staged as the restore would brick startup —
     # reject anything lacking the SQLite magic header, before touching disk.
     r = client.post("/api/settings/import", json={
-        "schema": server_mod.SETTINGS_BUNDLE_SCHEMA,
+        "schema": settings_router.SETTINGS_BUNDLE_SCHEMA,
         "server_config": {},
         "core_server_files": {
             "web_library.db": {"encoding": "base64",
@@ -171,7 +172,7 @@ def test_import_rejects_non_sqlite_db_payload(client, server_mod, tmp_path):
 
 def test_import_writes_custom_art_immediately(client, server_mod, tmp_path):
     r = client.post("/api/settings/import", json={
-        "schema": server_mod.SETTINGS_BUNDLE_SCHEMA,
+        "schema": settings_router.SETTINGS_BUNDLE_SCHEMA,
         "server_config": {},
         "core_server_files": {
             "playlist_covers/7.png": {"encoding": "base64",
@@ -186,7 +187,7 @@ def test_import_writes_custom_art_immediately(client, server_mod, tmp_path):
 def test_import_core_path_traversal_rejected(client, server_mod, tmp_path):
     secret = tmp_path.parent / "escape.txt"
     r = client.post("/api/settings/import", json={
-        "schema": server_mod.SETTINGS_BUNDLE_SCHEMA,
+        "schema": settings_router.SETTINGS_BUNDLE_SCHEMA,
         "server_config": {},
         "core_server_files": {
             "../escape.txt": {"encoding": "base64",
@@ -201,7 +202,7 @@ def test_import_core_undeclared_path_skipped_not_fatal(client, server_mod, tmp_p
     # A relpath outside the core allowlist is a warn-and-skip, not a refusal —
     # the rest of the bundle still applies.
     r = client.post("/api/settings/import", json={
-        "schema": server_mod.SETTINGS_BUNDLE_SCHEMA,
+        "schema": settings_router.SETTINGS_BUNDLE_SCHEMA,
         "server_config": {},
         "core_server_files": {
             "audio_cache/x.ogg": {"encoding": "base64",
@@ -289,7 +290,7 @@ def test_full_db_backup_restore_round_trip(client, server_mod, tmp_path):
 def test_export_fails_hard_when_db_snapshot_unavailable(client, server_mod, monkeypatch):
     # A backup that silently omits the library DB is a data-loss trap — the
     # export must error rather than hand back an incomplete-looking bundle.
-    monkeypatch.setattr(server_mod, "_snapshot_library_db", lambda: None)
+    monkeypatch.setattr(settings_router, "_snapshot_library_db", lambda: None)
     r = client.get("/api/settings/export")
     assert r.status_code == 500
     assert "library database" in r.json()["error"].lower()
@@ -299,16 +300,16 @@ def test_failed_import_disarms_staged_db_restore(client, server_mod, tmp_path, m
     # If a later write in phase 2 fails, the request 500s — but a staged DB
     # restore must NOT survive to swap in on the next restart.
     payload = _valid_db_bytes(tmp_path, name="incoming.db")
-    real_write = server_mod._atomic_write_file
+    real_write = settings_router._atomic_write_file
 
     def boom(target, data):
         if target.name == "config.json":          # last write of the commit
             raise OSError("disk full")
         return real_write(target, data)
 
-    monkeypatch.setattr(server_mod, "_atomic_write_file", boom)
+    monkeypatch.setattr(settings_router, "_atomic_write_file", boom)
     r = client.post("/api/settings/import", json={
-        "schema": server_mod.SETTINGS_BUNDLE_SCHEMA,
+        "schema": settings_router.SETTINGS_BUNDLE_SCHEMA,
         "server_config": {},
         "core_server_files": {
             "web_library.db": {"encoding": "base64",