Two transactions tagging overlapping models could each hold a tag row the other
wanted. tagId used ON CONFLICT DO UPDATE, which rewrites the row and therefore
write-locks it even though the name never changes, and each caller iterated in
whatever order it happened to have. That is what killed "Mushroom Clicker"
during AI run 21, while the collection watcher was importing and rule-tagging
the same tags.
tagId no longer rewrites unchanged rows, and applyAiResult, replaceRuleTags and
setTags all tag in sorted order, so locks are taken in the same sequence every
time. db.transaction retries a deadlock victim up to three times as well, which
covers the paths this doesn't — the victim rolled back and changed nothing, so
running it again is safe.
Measured: the old pattern deadlocks on demand (40P01), and the same collision
run 48 times through the new code fails zero times.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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