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 repro path in the demo checkout API by preventing over-reservation under concurrent requests and by handling expected “out of stock” failures without failing the whole concurrent scenario.

Changes:

• Add a live inventory availability re-check right before committing the reservation to avoid stale pre-checks under concurrency.
• Return reservation metadata (token + snapshot version) from the committed inventory record rather than the stale snapshot.
• Switch concurrent checkout scenario execution to Promise.allSettled, surfacing only “hard” failures while tolerating expected OutOfStock rejections.

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 post-delay availability guard and returns committed snapshot/version info.
demo_app/src/checkout/submit-order.ts	Uses allSettled to tolerate expected OutOfStock failures during concurrent scenario runs.

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[Copilot]

The concurrency window comment above the delay now reads like a still-present bug, but the new post-delay record.available guard changes the behavior. Update the comment to reflect that the delay is only simulating a race window and that availability is re-validated against the live record before commit (or remove the delay if it’s no longer intended).

[Copilot]

This treats expected failures by parsing error.message (prefix match) which is brittle and easy to break during refactors/localization. Consider introducing a typed OutOfStockError (or an error.code field) and switching this logic to a helper like isOutOfStockError(reason: unknown) so control flow isn’t coupled to the exact message text.