Know what happened after the timeout.
Compare what the client saw with what the service committed. A failed response does not establish a failed write.
Useful result
The first reservation commits at 120ms; the client times out at 1,000ms.
All use cases
Engineering
Give engineering evidence it can act on.
Investigate whether retrying a timed-out write creates a duplicate side effect, then return a reproducible case before release.
Service engineering, quality engineering, and release owners
Reservation Replay BenchSynthetic fixture
R2 · delayed response after commit
0ms
Attempt A1 · key k-A
120ms
Commit r-901 · available 18
1,000ms
Client timeout
1,100ms
Retry A2 · key k-B
1,220ms
Commit r-902 · available 16
Invariant comparison
R11 / 18Baseline
R22 / 16Fail
R31 / 18Stable-key override
R4409Changed payload
Hold candidate pending client review
The question
“Create a reusable bench so QA can check whether retrying one checkout reserves stock twice. Use synthetic inventory only.”
The repository, test runner, telemetry, and release process remain authoritative. The example is a fictional isolated fixture.
Send back a case engineering can reproduce.
QA adds the response-after-commit fault. The agent runs bounded comparisons and keeps raw observations separate from inference.
Useful result
Changed retry keys create two reservations; a stable-key fixture override creates one.
Review the change, not only the conclusion.
Return a rerunnable package, unresolved questions, and separate proposals for client behavior, the bench, and agent guidance.
Useful result
Evidence narrows the next decision without pretending a patch shipped.
The evidence behind the result.
Numbers stay connected to their definitions, source records, and limits.
Baseline R1
1 / 18
Reservation / available
Reproduction R2
2 / 16
k-A → k-B
Comparator R3
1 / 18
Stable-key override
Negative control R4
409
Changed payload rejected
Inspect the source trail.
This demonstration uses internally consistent fictional fixtures. It is not a customer result or live external execution.
120ms: reservation r-901 commits; available quantity becomes 18
1,000ms: A1 client timeout; response not received
1,100ms: A2 retries with a different key; second commit at 1,220ms
The work moves. Responsibility stays clear.
Originates
Inventory Engineering
Contributes
Inventory Validation
Decides
Release owner
Decision remains with people
Hold the candidate pending client review. Do not increase retry count from this result.