Prove the lost update with one invented session
Start with an empty synthetic cart and two known add-item requests in the same disposable session. Control the overlap in a test harness so both read the starting state before either finishes. Record request outcomes and the final item IDs. This tests session data loss, not whether a purchase was charged twice.
- Compare a sequential baseline with the controlled overlapping sequence.
- Record the session storage driver and every endpoint that writes the cart.
- Use a correlation label rather than copying the actual session identifier into shared evidence.
A lock is only as useful as its scope
Laravel describes same-session route blocking and its supported lock drivers, explicitly excluding the cookie session driver. Applying it to only one of several competing writers may leave the other path uncoordinated. Check the actual framework version, shared lock store and expected maximum critical-section duration before proposing a change.
- Keep unrelated sessions independent; do not replace a per-session problem with one global cart lock.
- Define what the customer sees when the lock wait times out.
- Do not assume a lock with an expired lease still serializes a long request.
Acceptance includes the failure branch
An authored regression asserts that both intended item updates survive the controlled overlap, the sequential baseline remains correct and a lock timeout produces the agreed safe feedback rather than a false success. A separate disposable session must not inherit this cart. These are proposed checks, not executed evidence.
- Check response state as well as the final stored cart.
- Do not equate session blocking with payment or order idempotency.
- Keep real gateways, emails and fulfilment disabled on the test copy.
Non-fit and priced route
A controlled, deterministic ordinary lost-update reproduction may fit fix-one-bug-with-regression-test, from £295 after bounded reproduction and a fixed repair quote. An unexplained intermittent report, distributed session-store redesign, capacity testing or duplicate financial transactions does not fit that job; the current operator must first establish a safe reproduction or separately scope recovery. If evidence suggests cross-user disclosure, use the security process instead.
- Initial inputs are invented actions and expected cart items, framework/driver versions and a redacted sequence, not session cookies or source code.
- No production restart, spend or live checkout is authorised here; the price is not evidence of paying intent.
Sources and limits
- Laravel 12.x session blocking; MIT-licensed version-specific documentation Checked 2026-10-11.
- Requests using the same session may execute concurrently by default.
- Concurrent session-writing endpoints can lose session data.
- Session blocking requires an atomic-lock-capable cache driver and cannot use the cookie session driver.
- Lock and wait durations are bounded and a lock timeout can raise an exception.
- Current one-bug reproduction boundary Checked 2026-10-11.