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

This PR addresses the demo app’s checkout-race-condition by ensuring inventory reservations re-validate against live state at commit time, and by adjusting the concurrent checkout repro flow to tolerate expected out-of-stock outcomes.

Changes:

• Add a post-delay availability guard in reserveStock to prevent overselling under concurrent requests.
• Return committed snapshotVersion/reservationToken values from the live inventory record (instead of the stale snapshot).
• Update the concurrent race scenario to use Promise.allSettled and only fail on non-out-of-stock errors.

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 stock validation and returns committed version/token values to eliminate stale snapshot usage.
demo_app/src/checkout/submit-order.ts	Treats out-of-stock as an expected concurrent outcome by settling requests and filtering soft failures.

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[Copilot]

The comment above this block says the delay is an “Intentional bug”, but with the new post-delay record.available check this function is no longer relying on a stale pre-check. Please update/remove that comment so it doesn’t mislead future readers about the current behavior.

[Copilot]

runCheckoutRaceScenario treats out-of-stock as a soft failure by parsing error.message (startsWith("OutOfStock:")). This is brittle and couples callers to a specific error string; consider using a dedicated error type (e.g., class OutOfStockError) or a structured discriminator (e.g., error.name/code) exported from the inventory layer so the check remains stable if the message changes.