Drain the sync queue without duplicating completed visits
Reception returns briefly and drops again during sync. The same completed visit is sent twice, while a later note disappears after a failed batch.
- Focused work estimate
- 3h + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Idempotency · Queues · Retry design
Estimated field mix
- Mobile50%
- Distributed systems50%
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
The fictional Vale facilities team services equipment in basements with poor reception. Technicians receive assigned work orders, record checks, and attach synthetic equipment photos. The practice app uses an on-device database and a stub sync service; background location tracking is excluded.
Setup prerequisites
- Synthetic work orders and a revisioned sync contract
- An emulator with controllable connectivity and app lifecycle
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
- FIELD-102 · Commit a completed checklist item before showing it saved
- FIELD-101 · Tell technicians which work orders are available offline
- FIELD-103 · Make inspection inputs usable with large text
- FIELD-104 · Keep photo evidence attached after the app is suspended
- FIELD-105 · Explain why a work order is not ready to finish
Acceptance criteria
- Each queued operation has a stable identity and advances only after acknowledgement.
- Per-order dependencies preserve answer and completion ordering while unrelated orders can progress.
- Retry uses bounded backoff and keeps unacknowledged operations durable across restart.
Implementation constraints
- The fixture service deduplicates operation IDs; do not assume a timeout means the server rejected a write.
Verification to include
- Acknowledge a batch and verify only confirmed queue entries leave local storage.
- Drop a response after server acceptance and restart; retries keep the same IDs and produce one logical completion.
Deliverables
- Durable sync queue processor and interrupted-batch tests
Rollout and recovery
Limit initial batch size and observe backlog age; pause queue draining on repeated protocol errors without deleting pending work.
Value of the work
For the engineer: Practice durable local state, mobile lifecycle recovery, and conflict resolution in realistic offline workflows.
For the team: Review whether an engineer can protect field work through crashes, interrupted uploads, and reassignment.
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.