Source: task/spotify-token-resilience (plan/steward-linker-quality) — cold-cache fan-out fired up to 100 concurrent token POSTs (429 storm) and search didn't refresh-retry on a 401.
- service/spotify.js (new): makeSpotifyToken() single-flights the token fetch via an in-flight-promise cache so N concurrent cold/expired lookups share ONE POST /api/token; clears the promise on settle (success or failure) so a rejected fetch never poisons the cache. makeSpotifySearch() refreshes-and-retries once on a 401 and honors a bounded (capped) Retry-After on a 429, else throws (resolve-core nulls the candidate, as before).
- service/resolver.js: wires the factories with the real fetch + Date.now; value-cache + (expires_in-60)*1000 expiry math unchanged; external behavior (result shapes, USE_SPOTIFY degradation, /health, /resolve) identical.
- service/spotify.test.js (new): hermetic node:test coverage — single-flight (100 concurrent -> 1 fetch), re-fetch after expiry, failure clears in-flight, 401 refresh-retry + persistent-401 throw, bounded 429 backoff. Zero new deps.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
