refactor(server): move the metadata-enrichment subsystem into lib/enrichment.py (R3)

CHANGELOG.md

@@ -40,6 +40,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   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**.
+- **`lib/enrichment.py` — the metadata-enrichment subsystem leaves `server.py` (R3, move-only).** MusicBrainz / Cover-Art-Archive / AcoustID transport, the match-scorer glue, and the background enrichment worker (~930 lines, 61 defs) move out as one cohesive unit. Bodies are verbatim; the only changes are seam reads — `meta_db`/`config_dir`/`sloppak_cache_dir`/`art_cache_dir` and the two shared art helpers (`song_pack_art_exists`, `art_override_paths`, which stay in `server.py` for the art/delete routes) are reached through `appstate` at call time, and the User-Agent VERSION lookup is corrected for the module's new depth. `server.py` drives the worker through the module (`import enrichment`; the routes + scan lifecycle call `enrichment.X`); tests that faked the network on `server` now patch the same names on `enrichment` (module attribute resolved at call time, so one `setattr` reaches both the routes and the worker's internal callers). Acyclic — `enrichment` imports no `server`. Route table byte-identical; full suite green. `server.py`: 6,917 → 5,988.
 - **`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*

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`
-(6,917 — was 14,037; ratcheted by the R3 `MetadataDB` + `AudioEffectsMappingDB`
-extractions and fifteen `routers/` modules) ·
+(5,988 — was 14,037; ratcheted by the R3 `MetadataDB` + `AudioEffectsMappingDB`
+extractions and fifteen `routers/` modules; 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

@@ -92,13 +92,20 @@ def artist_page(name):
 get_progression_content = None
 builtin_diagnostic_filename = None
 running_version = None
+# Art helpers that stay in server.py (shared with the art/delete routes) but are
+# also called by the enrichment worker in lib/enrichment.py — injected as
+# callables to keep enrichment acyclic. art_cache_dir is server's ART_CACHE_DIR.
+art_cache_dir = None
+song_pack_art_exists = None
+art_override_paths = None
 
 _SLOTS = frozenset({
     "meta_db", "audio_effect_mappings", "tuning_providers",
     "config_dir", "dlc_dir", "dlc_dir_env",
     "static_dir", "sloppak_cache_dir", "audio_cache_dir",
     "get_progression_content", "builtin_diagnostic_filename",
     "running_version",
+    "art_cache_dir", "song_pack_art_exists", "art_override_paths",
 })