SetMaxOpenConns(1) forced every read (List/Get/GetPR/...) to queue behind
the single connection, so the dashboard's reads contended with the LCM's
writes. WAL already supports many concurrent readers, so raise the pool to 8
and instead serialize *writes* with a Store.writeMu. That keeps WAL's
single-writer rule and the revision-CAS read-then-write atomic regardless of
pool size, while reads now run in parallel across the pool.
Every write method takes writeMu (Upsert, PatchMetadata, UpsertPR/DeletePR,
the pr_check/pr_comment Replace* via inTx, the CDC outbox/offset writes,
project writes, reaction-tracker writes); reads take nothing. Added
TestConcurrentReadsAndWrites (16 writers + 16 readers) which passes under
-race.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
ba47212802