Cin pre-review pass on the false-positive risk. Three tightenings:
# 1. Bumped MB-search trust threshold from 0.6 → 0.85
`MusicBrainzService.lookup_artist_aliases` previously trusted any
MB search match scoring ≥ 0.6 combined (name-similarity + MB
relevance). For distinctive cross-script artists the user-reported
case targets (Hiroyuki Sawano, Сергей Лазарев, etc.) real matches
score ~1.0 — well above 0.85. The 0.6 floor was loose enough to
let in moderate matches for ambiguous names, risking aliases for
the wrong artist getting cached + applied.
Bumped to 0.85. Tighter without rejecting any of the legit
cross-script cases the PR is for.
# 2. Ambiguity gate — skip when results within 0.1 of best
When MB search returns multiple results all scoring high (within
0.1 of the best), the artist name is ambiguous — common name with
multiple distinct artists ("John Smith" returning 10 different
John Smiths). Pulling aliases for any one of them risks the wrong
artist's data bridging incorrectly to a file's tag.
Added explicit ambiguity detection: when 2+ results within 0.1,
skip alias lookup entirely + cache empty. Matches Cin's
"explicit > implicit" — the prior code just picked the highest
score blindly.
# 3. Diagnostic log when alias rescues a comparison
When the alias path triggers a PASS that direct similarity would
have FAILed, emit an INFO log: `Artist alias rescued comparison:
expected='X' vs actual='Y' (direct sim=0.00, alias 'Z' →
score=1.00)`.
Lets future bug reports trace which alias triggered which decision.
Doesn't change behavior — visibility only. Logs ONLY the rescue
case, not happy-path direct matches (no log spam).
# Tests added (5)
`test_artist_alias_service.py` (+3):
- `test_moderate_confidence_match_now_skipped_strict_threshold`
- `test_ambiguous_results_skipped`
- `test_unambiguous_high_confidence_match_succeeds`
`test_acoustid_verification_aliases.py` (+3):
- `test_alias_rescue_emits_info_log` — direct-fail + alias-pass
emits INFO log
- `test_no_log_when_direct_match_succeeds` — happy path quiet
- `test_no_log_when_alias_doesnt_help` — failed path also quiet
# Test infrastructure note
Logging tests use a directly-attached `ListHandler` on
`soulsync.acoustid.verification` (the actual logger name —
dot-separated by `get_logger`), NOT pytest's caplog. Same pattern
as the prior watchdog-test fix — caplog is intermittently flaky
in full-suite runs for soulsync namespace loggers. An owned
handler sidesteps both issues.
# Verification
- 85/85 matching tests pass (+5 from prior commit)
- 2543 full suite passes (+6 from prior, +85 PR-total)
- Ruff clean
- Reporter's Japanese + Russian regression tests still pass —
legit cross-script case (sim ≈ 1.0) clears the new 0.85
threshold easily
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