fix(runtime): preserve transactions on idempotency conflicts

[sskyy]

Summary

On PostgreSQL, when two dispatches carrying the same idempotency key arrive concurrently for the first time, the second dispatch's _DispatchIdempotency_ insert fails with a unique violation after the first one commits. A unique violation aborts the PostgreSQL transaction, and claimDispatchIdempotencyRow then reads the conflicting row inside that transaction, so the duplicate dispatch returned SQLSTATE 25P02 (current transaction is aborted) instead of the documented idempotency result (replayed, or the typed IdempotencyError).

The claim now uses INSERT ... ON CONFLICT DO NOTHING RETURNING on PostgreSQL, PGLite and SQLite, so a conflict is not an error, the transaction stays usable, and the stored state maps to the existing typed errors through one shared helper. MySQL, which has no dispatch transactions, keeps the previous unique-error path.

The defect was found by a downstream application (Mesh) while integrating its GenerationOutcome feature (issue #884 in that project's tracker). The application will consume the published interaqt fix instead of adding a local workaround.

Scope of the defect

Isolation level	Before	After
READ COMMITTED (default)	duplicate dispatch returns 25P02	duplicate dispatch returns replayed / typed IdempotencyError
SERIALIZABLE	40001, retried by runWithTransactionRetry	unchanged

Under SERIALIZABLE the framework's own flow already produced a retryable 40001 before this change: the winner's finish() reads the key after inserting it and the loser read it through load(), so PostgreSQL's serializable conflict detection reports a serialization failure for both INSERT forms. The fix therefore changes only the default isolation level. The SERIALIZABLE test is a pinned neighbouring cell, not a reproduction of the defect.

Review follow-up

• The conflict-safe path is selected with getSchemaDialect(db).name, like every other dialect decision in MonoSystem. A driver that declares no schemaDialect is treated as postgres; with the raw db.schemaDialect?.name read it silently kept the defect.
• New cells: a PGLite driver with no declared dialect (fails with the raw read), and a real-PostgreSQL SERIALIZABLE cell (passes before and after, labelled as such).
• The dimension registry row now names the isolation and dialect-resolution axes, and the undefined label in its last column is replaced by a description of the escape.

Validation

• Pre-fix check: with the pre-fix MonoSystem.ts, the READ COMMITTED real-PostgreSQL race and the PGLite claim-conflict cell fail (25P02); with the fix they pass.
• npm run check — passed.
• npm run test:postgres — 11 files, 53 tests passed; includes the two-Controller race for winner commit and winner rollback, and the SERIALIZABLE cell.
• npm test — 236 files passed, 15 skipped; 2,804 tests passed, 71 skipped.

🤖 Generated with Claude Code