Replay checkout retries without extending a hold
A flaky mobile connection retries the reserve call every minute. Each retry adds another ten minutes to the hold and can change the requested quantity.
- Focused work estimate
- 2h 30m + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Idempotency · Time semantics · API compatibility
Estimated field mix
- Backend70%
- API design30%
Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence.
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Project context
A fictional retailer sells bicycle parts from East and West warehouses. Cart reservations last ten minutes, payment callbacks arrive late, and warehouse counts occasionally need correction. The exercise has no real orders or payment integration.
Setup prerequisites
- Relational modeling
- Concurrent API requests
- State transitions
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
Acceptance criteria
- The same order request replays the original reservation and expiry.
- Changing quantity or warehouse under the same request key returns conflict.
- An expired reservation remains expired when the request is replayed.
Implementation constraints
- Bind the request identity to retailer and order; a replay is not a renewal.
Verification to include
- Retry after nine minutes and assert the original expiry remains.
- Replay with changed quantity and replay after expiry; inspect both responses.
Deliverables
- Reservation idempotency contract and time-controlled examples
Rollout and recovery
Enable replay behavior for new keys; retain legacy key interpretation until outstanding holds expire.
Value of the work
For the engineer: Practice inventory invariants and timed state transitions while balancing customer experience with operational repair.
For the team: Inspect an engineer's handling of overselling, delayed callbacks, warehouse boundaries, and reversible schema changes.
Evidence boundaries
Outcome Evidence: Tests, patches, and runbooks are requested deliverables. They become Outcome Evidence only through a qualified Mission and immutable Evidence IDs.
Ownership Evidence: Independent adaptation must be observed under a declared verification policy and cite immutable Evidence IDs. Completing a planning ticket establishes no Ownership Evidence.