Problem

Fixes #29138

When PlanetScale's vttablet kills a transaction server-side (e.g., 20-second timeout), @prisma/adapter-planetscale silently swallows the COMMIT failure. Prisma resolves the operation as successful and returns data from the uncommitted transaction, but nothing is actually persisted. This causes silent data loss in production.

Root Cause

In startTransactionInner(), the outer Promise is resolve()d inside the conn.transaction() callback — before the transaction completes. When COMMIT later fails:

1. The error hits .catch()
2. .catch() calls reject(error) — but the Promise is already resolved, so this is a no-op
3. .catch() returns undefined, so txResultPromise resolves successfully
4. commit() awaits txResultPromise → resolves → silent data loss

Fix

One-line change: replace return reject(error) with throw error.

When we throw instead of calling the already-settled reject():

• txResultPromise (the .catch() chain result) rejects with the error
• commit() awaits txResultPromise → throws → error propagates to the consumer

Tests

Added 3 test cases:

• commit succeeds when conn.transaction() resolves — no regression on happy path
• commit throws when conn.transaction() rejects after COMMIT failure — verifies the fix
• rollback does not throw (RollbackError is swallowed) — no regression on rollback

Summary by CodeRabbit

• Bug Fixes

  • Improved error handling in transaction operations to ensure errors propagate correctly during commit failures.

• Tests

  • Added comprehensive test coverage for transaction commit, rollback, and error scenarios in the PlanetScale adapter.