Wire catalog cascade into GET /library/ via fuzzySearchLibrary (BS#972)

[jakebromberg]

Summary

The catalog-track-search cascade (CTA → LML /lookup) lived only inside searchLibrary, which GET /library/search calls. Catalog clients (dj-site useSearchCatalogQuery, iOS searchLibrary) hit GET /library/ instead, which calls fuzzySearchLibrary and tops out at tsvector + trigram. Flipping CATALOG_TRACK_SEARCH_CTA_ENABLED / CATALOG_TRACK_SEARCH_DISCOGS_ENABLED to true in prod had no observable effect on the catalog page or the iOS app, and matched_via was always absent from AlbumSearchResult[] responses — making three already-merged client surfaces (MatchedTrackBadge, modern MatchedTrackChips, classic MatchedTrackChips) dormant.

This PR pushes the cascade down one layer:

• searchLibraryByCTARaw and searchLibraryByTrackRaw are new, returning TaggedLibraryViewEntry[] (i.e. LibraryArtistViewEntry plus an optional matched_via). The existing searchLibraryByCTA / searchLibraryByTrack are kept as enriched-shape wrappers so request-line callers (artistPlusAlbum, swappedInterpretation, songAsArtist, trackOnCompilation) are unaffected.
• Track 2's LRU cache moves to the raw layer so both catalog and request-line callers share one cache.
• searchLibraryBothMode now owns the full tsvector → trigram → CTA → LML cascade and returns TaggedLibraryViewEntry[].
• fuzzySearchLibrary's both-mode branch (the dj-site shape, where artist_name === album_title) routes through searchLibraryBothMode and inherits the cascade. Split-field queries stay on the legacy fuzzy path — out of scope.
• serializeLibraryArtistViewEntry carries matched_via through to the wire (LibraryArtistViewResponse now declares the optional field).

Both feature flags default off, so a deployment that hasn't opted in is byte-identical to before. This is wiring only — no behavior change without a flag flip.

Acceptance criteria (from #972)

• GET /library/?artist_name=q&album_title=q&n=10 with CATALOG_TRACK_SEARCH_CTA_ENABLED=true returns matched_via: [{ title, source: "cta" }, …] on tsvector+trigram 0-hits (new unit + integration tests assert this).
• Same shape with CATALOG_TRACK_SEARCH_DISCOGS_ENABLED=true returns matched_via: [{ title, source: "discogs…" }] on CTA misses (new integration test against the existing Track 2 fixtures hits vi scose poise → Confield).
• Both flags off: /library/ responses are byte-identical to today (cascade no-op verified by the existing library.spec.js + ranking suites).
• Direct artist/album tsvector hits never carry matched_via (unit + integration test).
• No regression in searchForAlbum request shape (code_letters lookup, on_streaming-only browse, missing-params 400 unchanged).
• Integration test: with both flags on, /library/?artist_name=vi+scose+poise&album_title=vi+scose+poise returns the Confield row with matched_via.source matching discogs* (uses the existing Track 2 mock-LML fixture; no live LML required in CI).
• Latency budget preserved: enabled-flag path stays within the existing LIBRARY_SEARCH_ENRICHMENT_BUDGET_MS artwork race; the cascade adds at most one CTA SQL + one LML /lookup per 0-hit (unchanged from /library/search).

Test plan

• npm run test:unit (1991 passed; new fuzzySearchLibrary Both-mode cascade block + existing searchLibrary cascade block both green)
• npm run typecheck (clean across all workspaces)
• npm run lint (0 errors)
• npm run format:check (clean)
• npm run build (all workspaces)
• npm run test:integration (new GET /library cascade — catalog route serves matched_via (BS#972) block plus existing library.spec.js regressions — exercised in CI via ci:testmock)

Related

• Closes Wire searchLibrary cascade into GET /library/ so catalog clients see matched_via #972
• Parent epic: [Epic] E1 — Track 1: CTA compilation search #814 (E1 — Track 1 CTA compilation search). This is the wiring step that E1-3: Integrate searchLibraryByCTA as fallback in searchLibraryBothMode #818's stated acceptance criterion implied.
• Sibling: [Epic] E2 — Track 2: BS-side proxy to LML's /lookup (catalog-track-search v2) #815 (E2 — Track 2 LML proxy). Same wiring; both layers fixed by this PR.
• iOS consumers (unblocked): WXYC/wxyc-dj-tool-ios#13 (decode + badge), WXYC/wxyc-dj-tool-ios#15 (track-title forward to bin).
• dj-site consumers (unblocked): E3-4: Update SearchForm.tsx help text — remove "Coming later" and add track example dj-site#497 (classic chips), E3-5: Feature flag CATALOG_TRACK_SEARCH_UI_ENABLED + .env documentation dj-site#498 (modern chips).
• Plan: WXYC/wiki/plans/catalog-track-search.md §4.1, §5.1.
• API contract: wxyc-shared/api.yaml:1072-1079 (AlbumSearchResult.matched_via).