fix(checkout-api): resolve checkout-race-condition

[Spkap]

Summary

Resolve checkout-race-condition for checkout-api with a validated ReplayX patch candidate.

Changed Files

• demo_app/src/inventory/reserve-stock.ts
• demo_app/src/checkout/submit-order.ts

Validation

• Concurrent checkout repro: exit 0
• Sequential checkout sanity: exit 0

Rollback

Revert the live inventory guard and concurrent checkout settlement handling.

[Copilot]

Pull request overview

Resolves the checkout race condition by preventing overselling during concurrent reservations and making the concurrent checkout scenario treat expected out-of-stock outcomes as non-fatal.

Changes:

• Add a post-delay (commit-time) availability check in reserveStock to prevent stale pre-checks from overselling.
• Return reservation metadata based on the committed inventory record version.
• Update concurrent checkout scenario execution to use Promise.allSettled and ignore expected out-of-stock failures.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
demo_app/src/inventory/reserve-stock.ts	Adds commit-time inventory guard and aligns returned reservation metadata with committed state.
demo_app/src/checkout/submit-order.ts	Uses allSettled for concurrent runs and only escalates non-out-of-stock failures.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

The out-of-stock guard after the delay fixes the TOCTOU behavior, but the nearby comment about an “Intentional bug” making the pre-check stale is now misleading (the stale pre-check no longer causes an incorrect commit). Consider updating/removing that comment and/or removing the earlier snapshot-based pre-check to avoid keeping a stale-check pattern in the example.

[Copilot]

Filtering expected failures by checking error.message.startsWith("OutOfStock:") is brittle (message text is not a stable API) and makes it easy to accidentally treat a real error as ignorable after a message change. Prefer a typed error (e.g., class OutOfStockError extends Error) or an explicit error code/name check, ideally via a small helper like isOutOfStockError(reason).