Move a booking only if its current revision still matches
An agent reschedules a booking from an old browser tab after a colleague already moved it. Add revision-aware rescheduling and retain the original slot until the new operation is settled.
- Focused work estimate
- 2h 45m + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Optimistic locking · State machines · Compensation
Estimated field mix
- Integrations50%
- Backend30%
- 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 consultancy books appointments across time zones. The first connector duplicates events after timeouts and offers slots during stale calendar sync. Use a local calendar-provider double and synthetic calendars.
Setup prerequisites
- Create a local provider double for free/busy, event creation, updates, cancellation, and expiring tokens.
- Use synthetic calendars and an injected clock; no calendar account or outgoing invitation is required.
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
- CAL-101 · Reject local times that do not identify one instant
- CAL-102 · Merge overlapping busy intervals before offering slots
- CAL-103 · Label unavailable or stale free/busy data instead of showing open slots
- CAL-104 · Reserve a slot atomically when two customers choose it
- CAL-105 · Reconcile a create-event timeout before trying again
Acceptance criteria
- Reschedule requests include the expected booking revision and are rejected when stale.
- The proposed new slot passes reservation and availability checks before the provider update.
- Provider failure or uncertainty leaves a documented pending/conflict state and does not silently mark both slots free.
Implementation constraints
- Use provider conditional updates when the adapter supports them.
- Record before and proposed intervals in an append-only operation record.
Verification to include
- Reschedule an unchanged booking and verify one final interval and incremented revision.
- Race two reschedules and simulate a provider timeout; verify explicit conflicts and no duplicate successful move.
Deliverables
- Rescheduling state transitions and race/failure cases
Rollout and recovery
Enable rescheduling after create reconciliation is stable; fall back to operator resolution for uncertain provider updates.
Value of the work
For the engineer: Practice time modeling, conflict-safe booking, external state reconciliation, and credential lifecycle boundaries.
For the team: Review whether integration work protects appointment correctness and offers clear recovery when a provider is uncertain.
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.