- db: translate INSERT OR IGNORE ... SELECT to ON CONFLICT DO NOTHING
(VALUES-only regex left SELECT form untranslated -> PG syntax error);
register task_audit_loop_state (task_id) in _OR_REPLACE_PK so PG
INSERT OR REPLACE becomes a real upsert instead of DO NOTHING.
- server: _backfill_default_quotas uses SAVEPOINT containment and no
longer commits the caller's transaction, so a backfill failure cannot
roll back init_db's migrate ALTERs.
- worker: _coord_child_rows rolls back before column-fallback retries so
a missing-column failure on PG does not cascade into
InFailedSqlTransaction.
- tests: test_pg_init_fix.py (translation, SQLite backfill/upsert,
real-PG fresh-init + merge + upsert + backfill containment, skipped
without CLOUD_TEST_PG_DSN/driver).
