refactor(server): move the metadata-enrichment subsystem into lib/enrichment.py (R3) (#861)

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

MusicBrainz / Cover-Art-Archive / AcoustID transport, the match-scorer glue, and
the background enrichment worker (~930 lines, 61 defs) leave server.py as one
cohesive unit. Bodies are verbatim; the only changes are seam reads:

  meta_db / config_dir / sloppak_cache_dir / art_cache_dir -> appstate.<slot>
  _song_pack_art_exists / _art_override_paths (stay in server.py for the art +
    delete routes) -> appstate.<callable> (new seam slots, injected by reference)
  _env_flag -> env_compat.env_flag_compat (the existing identical helper)
  _artist_title_from_filename -> imported from metadata_db (its home)
  the User-Agent VERSION lookup: Path(__file__).parent ->
    Path(__file__).resolve().parents[1] (lib/enrichment.py -> app root)

server.py drives the worker through the module (import enrichment; the routes +
scan lifecycle call enrichment.X). Tests that faked the network on `server`
(_mb_http_get, _enrich_network_enabled, _caa_http_get, ...) now patch the same
names on `enrichment` — the module attribute is resolved at call time, so one
setattr reaches both the routes and the worker's internal callers. Acyclic:
enrichment imports appstate/appconfig/dlc_paths/metadata_db/mb_match/
acoustid_match/sloppak/loosefolder, never server.

server.py: 6,917 -> 5,988 (-929).

Verified: pyflakes clean (bar the pre-existing File/safe_join/tuning_name/ET);
route table IDENTICAL (143); full pytest 2400 passed (140 enrichment/art cases
incl the offline-safety + transport-error-pauses-pass contracts that fake the
network); test_packaging 44 passed (enrichment.py resolves under lib/); eslint 0.
Boot smoke: /api/enrichment/status + POST /kick serve from the new module.

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

* test: reset enrichment worker state between tests (CodeRabbit)

lib/enrichment.py now owns the worker, and it stays imported for the whole
session while the `server` fixtures pop-and-reimport `server` — so the cancel
Event / status dict / caches would leak across tests, and a stale `_enrich_cancel`
could short-circuit a later direct `_background_enrich()`. An autouse conftest
fixture clears that process-global state before each test.

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

* test: tighten the enrichment-reset fixture (CodeRabbit)

Narrow the import guard to ImportError (not blind Exception, BLE001), and stop
clearing _caa_index_locks — it's guarded by _caa_index_locks_guard, so an
unlocked clear() would race a still-alive worker, and its per-release mutexes
carry no test state.

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

---------

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

tests/conftest.py

@@ -9,6 +9,36 @@ import structlog
 _LOGGING_NAMES = ("feedBack", "uvicorn", "uvicorn.error", "uvicorn.access")
 
 
+@pytest.fixture(autouse=True)
+def _reset_enrichment_state():
+    """Reset the enrichment worker's process-global state between tests.
+
+    The `server` fixtures pop-and-reimport `server`, but `lib/enrichment.py`
+    (which now owns the worker) stays imported for the whole session, so its
+    module globals — the cancel Event, the status dict, the caches — would
+    otherwise leak across tests. A test that set `_enrich_cancel` (or a stale
+    `running` status) could silently short-circuit a later direct
+    `_background_enrich()` call. Clear it up front so each test starts clean.
+    """
+    try:
+        import enrichment
+    except ImportError:
+        yield
+        return
+    enrichment._enrich_cancel.clear()
+    enrichment._enrich_pending_pass = False
+    enrichment._enrich_status.update(
+        {"running": False, "processed": 0, "last_pass_at": None,
+         "total": 0, "matched": 0, "current": None})
+    enrichment._enrich_last_fetch = 0.0
+    enrichment._artist_alias_cache.clear()
+    # _caa_index_locks is deliberately left alone: it's guarded by
+    # _caa_index_locks_guard, so clearing it here (unlocked) would race a
+    # still-alive worker thread, and its entries are stateless per-release
+    # mutexes that don't leak test state anyway.
+    yield
+
+
 @pytest.fixture()
 def isolate_logging():
     """Restore feedBack / uvicorn logger state after each test.