create_async_engine had no connect_args and there was no PRAGMA
anywhere in the repo. SQLite's default rollback-journal mode lets a
writer block every reader for the duration of its transaction, and a
second writer arriving while one is already active fails immediately
with "database is locked" rather than waiting at all - realistic given
five concurrent background tasks (scheduler, confirmation poller, RBF
bumper, two reconcilers) plus every HTTP handler share one file, and
nothing previously handled that error.
app/db/base.py now registers a "connect" event on the engine that sets
journal_mode=WAL, synchronous=NORMAL and a 5-second busy_timeout on
every new DBAPI connection - applied only when the dialect is sqlite,
so a future PostgreSQL DATABASE_URL is unaffected. WAL lets readers and
writers proceed without blocking each other, and busy_timeout gives a
second writer a real window to wait instead of failing instantly.
Left out: an explicit application-level retry wrapper for "database is
locked" in the background loops, the other half of the proposed fix -
busy_timeout already gives SQLite itself several seconds to resolve
writer-vs-writer contention before ever raising, and every background
loop already catches and logs an unhandled exception before its next
scheduled tick, which is itself a retry, just not an immediate one.
Suite grows from 211 to 214 tests. BUGS.md moves B-39 to Previously
fixed.
