Stop interpreting offset-free scans as server-local time
A carrier sends 2025-11-02 01:30 in its configured New York time zone. The importer guesses one occurrence during the clock change and displays delivery before pickup.
- Focused work estimate
- 3h + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Time zones · Data normalization · Ambiguity handling
Estimated field mix
- Data engineering100%
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
- Normalize explicit-offset timestamps to UTC.
- Quarantine ambiguous or nonexistent local times instead of guessing.
- Preserve original timestamp text and normalization policy version.
Implementation constraints
- Use explicit carrier time-zone configuration; process time zone cannot define event meaning.
Verification to include
- Normalize equivalent UTC and offset timestamps to one instant.
- Quarantine repeated-hour and skipped-hour local timestamps.
Deliverables
- Timestamp normalization policy and clock-change fixtures
Rollout and recovery
Shadow-normalize historical fixtures and review differences before switching timeline timestamps.
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.