Reconnect the map without losing updates between snapshot and stream
The dashboard downloads a vehicle snapshot and opens the live stream afterward. Updates during that gap never arrive, so a van appears stale until its next fix.
- Focused work estimate
- 3h 30m + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Snapshot consistency · Replay · Race conditions
Estimated field mix
- Real-time systems60%
- Distributed systems40%
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 Cedar delivery depot dispatches vans through a browser map and accessible list. Synthetic telemetry arrives through a gateway with device sequence numbers. This is operational fleet software practice; no real driver tracking, employee scoring, or routing safety guarantee is part of the project.
Setup prerequisites
- Synthetic vehicle telemetry with device sessions and sequence numbers
- Dispatch assignment and authorized region API contracts
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
Acceptance criteria
- The snapshot supplies an authorized region identity and exact stream watermark.
- Buffered or replayed events after that watermark apply once after snapshot installation.
- Expired watermarks, buffer overflow, and mismatched region data trigger explicit resync rather than a partial-current view.
Implementation constraints
- Document the snapshot/replay boundary contract; use a bounded buffer and synthetic trace harness.
Verification to include
- Inject movement during snapshot loading and confirm the final position includes it exactly once.
- Expire the watermark and switch region during recovery; no mixed-region positions or falsely current state appears.
Deliverables
- Snapshot/stream handoff protocol and gap-recovery harness
Rollout and recovery
Pilot with forced reconnects; keep the map visibly stale and commands disabled until a coherent snapshot is installed.
Value of the work
For the engineer: Practice geospatial boundaries, stream ordering, snapshot recovery, and concurrent operational commands.
For the team: Inspect whether a developer keeps dispatch decisions grounded in current authorized data and exposes uncertainty during outages.
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.