Live LML timeout: bump to 30s + synthesized-URL fallback on catch (closes #873)

[jakebromberg]

Summary

Two changes that together close #873:

• apps/backend/services/lml/lml.client.ts: TIMEOUT_MS 5s → 30s. Matches jobs/flowsheet-metadata-backfill/lml-fetch.ts. Runtime path is fire-and-forget so this holds a Node promise + LML socket, not a user-visible request.
• apps/backend/services/metadata/enrichment.service.ts: catch arm now writes the three synthesized YouTube/Bandcamp/SoundCloud search URLs via SearchUrlProvider. Crucially, metadata_attempt_at stays unset on the failure path — the row remains eligible for the drift-repair sweep so the real artwork/Discogs/Spotify/Apple match can land on a future attempt. The WHERE clause narrows on metadata_attempt_at IS NULL to stay idempotent with the backfill.

Cold-cache LML lookups currently land at 8-18s (measured against prod 2026-05-19). Every miss aborts to LmlClientError, the catch arm Sentry-reports but writes nothing, and ~70% of an active show's rows surface as blank artwork on iOS until the 06:00 UTC drift-repair sweep catches up.

Measurements (2026-05-19, post-schema-fix)

Direct prod POST /api/v1/lookup:

Artist / Track	wall	search_type	api_calls
22 Beaches / Breathing	8.0s	compilation	5
El Keamo / Esperando	11.7s	compilation	6
Rita Villa / Czardas	18.3s	compilation	7
Sonido Dueñez / La Piragua	12.9s	compilation	5
Amy Gadiaga / Imma Pick You Up	13.2s	compilation	5
The Fly Girlz / Born 2 Be Fly	17.0s	compilation	9
Felt / Evergreen Dazed (warm)	0.5s	direct	0

Cold-cache compilation lookups dominate the wall-time — every one exceeds the existing 5s budget. The cascade depth fix lives upstream in WXYC/library-metadata-lookup#337 (A2/A3 already merged on main, not yet promoted to prod). This PR is the BS-side mitigation.

Test plan

• Unit: on LML failure, row updated with the 3 synthesized URLs only (no artwork_url/discogs_url/spotify_url/apple_music_url/artist columns).
• Unit: on LML failure, metadata_attempt_at NOT in the SET clause.
• Unit: on LML failure, WHERE clause narrows on metadata_attempt_at IS NULL (idempotent with backfill).
• Existing unit: on LML success-with-match, metadata_attempt_at stamped via NOW().
• Existing unit: on LML success-no-match (search URLs only), metadata_attempt_at stamped.
• Local: npm run test:unit — 1987/1987 pass.
• Local: npm run lint — 0 errors.
• Local: npm run typecheck — clean.
• Local: npm run format:check — clean.
• Post-merge prod verification (24h after deploy): re-query affected entries from Live LML metadata enrichment silently fails on most cold-cache lookups (5 s timeout, no catch-arm fallback) #873 (5210314, 5210316, 5210319, 5210327, 5210328, 5210336, 5210337, 5210340) and confirm artwork_url populated or at least the 3 search URLs present.

Related

• Perf regression in /api/v1/lookup: cold-cache compilation queries now 9-17s (was <5s pre-2026-05-13) library-metadata-lookup#337 — the LML-side cascade-depth regression this PR mitigates (paired ticket).
• Tune Sentry capture for LML failures in metadata enrichment (subsystem='metadata') #692 — Sentry capture tuning, superseded by [Epic G] Capture enrichment-outcome quality (all-null result), not just LML client throws #969 (closed via [G2] Resolve BS#692: pick Sentry capture disposition for subsystem=metadata #904's superseded path).
• Re-emit liveFs SSE event after metadata enrichment UPDATE lands #628 — SSE re-emit race, symptom amplifier (separate fix).
• [Epic G] Capture enrichment-outcome quality (all-null result), not just LML client throws #969 — replacement enrichment-outcome instrument; baseline week starts post-merge.

Closes #873.