Preserve idempotency semantics across client version upgrades
A client retries an inventory reservation with the same key after upgrading its API version.
- Focused work estimate
- 3h 30m + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Idempotency · Compatibility
Estimated field mix
- API design50%
- Distributed systems30%
- Backend20%
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 inventory platform must replace a legacy availability response. Existing partners upgrade on different schedules, and the team needs a versioned transition.
Setup prerequisites
- Create two local API versions and synthetic partner clients with different upgrade schedules; no real partner traffic.
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
Acceptance criteria
- Define whether keys bind to normalized domain intent or transport version.
- Reject conflicting reuse consistently.
- Prevent duplicate domain effects across supported routes.
Implementation constraints
- Document the chosen scope rather than silently translating incompatible requests.
Verification to include
- Replay equivalent supported requests under the chosen policy.
- Reject a changed reservation under the same key.
Deliverables
- Cross-version idempotency contract.
Rollout and recovery
Retain original operation facts during migration.
Value of the work
For the engineer: Practice public-contract design, compatible evolution, and client lifecycle management.
For the team: Provide a predictable migration that keeps supported integrations inspectable and recoverable.
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.