Define the preference change envelope with source position
The consumer sees a timestamp and payload but cannot distinguish two changes committed in the same millisecond.
- Focused work estimate
- 1h 30m + prerequisites
- Priority in the scenario
- Medium
- Engineering practice
- Data contracts · Ordering
Estimated field mix
- Data engineering60%
- API design20%
- Distributed systems20%
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 messaging service builds a read model from database changes. Restarts and schema changes can re-enable preferences that customers disabled.
Setup prerequisites
- Create synthetic preference records and a replayable local change log.
- Use adapters or fixtures without provisioning a production broker.
Preceding work
No earlier ticket is required. Complete the project setup above.
Acceptance criteria
- Include stable source position, record identity and operation.
- Separate source commit time from consumer receipt time.
- Validate the envelope version before applying changes.
Implementation constraints
- Use fabricated positions from a deterministic local log.
Verification to include
- Parse two same-time changes with distinct positions.
- Reject an unknown envelope version without moving the checkpoint.
Deliverables
- Change envelope schema
Rollout and recovery
Publish the contract before consumer rollout; quarantine unsupported versions.
Value of the work
For the engineer: Practice change-feed ordering, snapshots and privacy-preserving deletion.
For the team: Review whether replicated customer preferences remain correct during recovery.
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.