Stop an opt-out retry from being lost behind an older opt-in event
Preference events reach a delivery replica out of order. A delayed older opt-in restores eligibility after a newer opt-out.
- Focused work estimate
- 5h + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Event ordering · Consistency
Estimated field mix
- Distributed systems60%
- Privacy engineering40%
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 event workspace offers optional product announcements and operational booking messages. Its product policy treats these as separate purposes. A stale audience cache currently sends optional messages after a member opts out. The brief implements fictional preference rules and makes no legal-consent certification.
Setup prerequisites
- Create synthetic members, versioned notice text and two purpose-tagged message types.
- Use a fake dispatch provider with controllable queueing and acknowledgement; send no real messages.
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
Acceptance criteria
- Apply a subject/purpose ordering rule with comparable revisions.
- Ignore older duplicates while preserving their receipt for bounded diagnosis.
- Expose replica freshness and define dispatch behavior when current ordering cannot be established.
Implementation constraints
- Wall-clock arrival order is not a reliable source revision; document the authority issuing revisions.
Verification to include
- Deliver opt-out, then older opt-in, then duplicate opt-out and verify current state remains disabled.
- Create a missing-revision gap and verify optional dispatch follows the declared fail-closed or authoritative-read path.
Deliverables
- Replica ordering protocol and event permutation tests
Rollout and recovery
Canary replica reads with authoritative comparisons; disable replica-based optional dispatch if gaps cannot be resolved.
Value of the work
For the engineer: Practice purpose modeling, versioned user choices, dispatch-time checks and consistency under retries.
For the team: Create an inspectable preference workflow that can be reviewed against a company-approved communication policy.
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.