Keep a late pickup scan from undoing delivered status
A DELIVERED scan arrives at 16:00, followed by a delayed PICKED_UP scan from 08:00. The tracking card switches back to In transit because it uses receipt order.
- Focused work estimate
- 2h 30m + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Event-time processing · Determinism · Read models
Estimated field mix
- Data engineering80%
- 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 delivery marketplace receives JSON batches from three carriers. One uses local timestamps, another retries whole batches, and a third corrects delivery scans. Customer support needs a stable timeline rather than the last payload received.
Setup prerequisites
- JSON schema validation
- SQL queries
- Event-time concepts
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
Acceptance criteria
- Build the timeline from event time with a documented deterministic tie-breaker.
- Retain late scans without regressing current delivery state.
- Represent inconsistent event sequences with a visible anomaly reason.
Implementation constraints
- Receipt time remains diagnostic information, not a substitute for event time.
Verification to include
- Import pickup and delivery in both arrival orders and compare projections.
- Add a pickup dated after delivery and inspect the anomaly.
Deliverables
- Tracking projection and out-of-order fixtures
Rollout and recovery
Compare projections in a shadow table; switch reads after reviewing differences.
Value of the work
For the engineer: Practice ingestion contracts, deduplication, event-time reconciliation, and replayable data repair.
For the team: Examine how an engineer preserves source lineage and handles bad partner data without losing valid business events.
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.