Previous commit only populated `artists.aliases` for artists the MB
worker had enriched. But the AcoustID verifier (next commit) needs
aliases for ANY expected artist — including:
- Artists not yet in the user's library (first download)
- Artists in the library where MB enrichment hasn't run yet
- Artists where MB enrichment ran but found no MBID (NULL aliases)
This commit adds a multi-tier resolution helper that fills those
gaps without thrashing the MB API.
# Multi-tier resolution
`lookup_artist_aliases(artist_name) -> list[str]`:
1. **Library DB** (fast path): existing `get_artist_aliases` lookup
by name. No network. Most common path once the worker has
enriched everything.
2. **Cache** (existing `musicbrainz_cache` table, entity_type=
`artist_aliases`): a prior live lookup for this name. Empty
cache hit is respected (don't re-query when MB previously had
nothing).
3. **Live MB**: search artist by name → pick highest-confidence
match (combined name-similarity + MB relevance) → fetch aliases
for that MBID → cache the result.
Always returns a list (possibly empty), never raises. Empty result
on any tier means "no alternate spellings found, fall back to
direct match" — identical to the pre-fix behaviour.
# Threshold gate
Live lookup only trusts the MB search result when combined
similarity score >= 0.6. Below that, we'd be guessing at the wrong
artist — searching `John Smith` returns multiple John Smiths and
pulling aliases for one of them could mismatch. Cache the empty
result so we don't keep re-searching the same low-confidence name.
# Performance contract
Critical for the verifier path: 100 quarantine candidates with the
same expected artist must NOT trigger 100 MB API calls. Cache hit
on second + subsequent calls per unique artist name. Verified by
test pinning the call counts.
# Tests added (8)
- Tier 1 library DB hit — no MB API call fired
- Tier 3 live MB lookup → search → fetch → returns aliases
- Tier 2 cache hit on second call — no re-query
- Empty input → empty return + no API call
- Network failure on search → empty + cached so we don't retry
- No search results → empty + cached
- Low-confidence match (sim < 0.6) skipped — defends against
picking the wrong artist
- Library row exists but aliases NULL → falls through to live
lookup (defends against the half-enriched state)
# Verification
- 31/31 service tests pass (8 new + 23 prior)
- Ruff clean
15244f24cf