Define ReminderEvaluation domain types and interfaces
epic-assignment-follow-up-reminders-services-task-001 — Create the Dart domain types and abstract interfaces for the ReminderEvaluationService. Define the ReminderEvaluationResult sealed class with variants none, remind, and escalate. Define the ReminderEvaluationService abstract interface with its evaluate() method signature accepting assignment ID and org thresholds.
Acceptance Criteria
Technical Requirements
Implementation Notes
Use Dart 3 sealed classes (`sealed class ReminderEvaluationResult {}`) so the compiler enforces exhaustive pattern matching in all consumers — this eliminates silent unhandled cases at call sites. Place all types under `lib/domain/reminders/` following the project's existing domain layer conventions. Do not mix repository interfaces into this file; keep it a pure domain model file. `OrgReminderThresholds` should use `const` constructors to allow compile-time constant usage in tests.
Ensure `escalateAfterDays >= remindAfterDays` is documented as a precondition (enforce via assertion in debug mode).
Testing Requirements
Unit tests are not required for pure type definitions, but a compile-time test file should assert that exhaustive switch on `ReminderEvaluationResult` covers all three variants without a default case. Verify that `dart analyze` passes with zero issues. Include a brief smoke test instantiating each variant and asserting type identity.
The idempotency window (how long after a reminder is sent before another can be sent for the same assignment) is not explicitly specified. An incorrect window — too short, duplicate reminders appear; too long, a resolved and re-opened situation is not re-notified. This ambiguity could result in user-visible bugs post-launch.
Mitigation & Contingency
Mitigation: Before implementation, define the idempotency window explicitly with stakeholders: a reminder is suppressed if a same-type notification record exists with sent_at within the last (reminder_days - 1) days. Document this rule as a named constant in the service with a comment referencing the decision.
Contingency: If the window is wrong in production, it is a single constant change with a hotfix deployment. The notification_log table allows re-processing without data migration.
For organisations with thousands of open assignments (e.g., NHF with 1,400 chapters), the daily scheduler query over all open assignments could time out or consume excessive Supabase compute units, especially if the contact tracking query lacks proper indexing.
Mitigation & Contingency
Mitigation: Add a composite index on assignments(status, last_contact_date) before running performance tests. Use cursor-based pagination in the scheduler (query 500 rows at a time). Run a load test with 10,000 synthetic assignments as described in the feature documentation before merging.
Contingency: If the query is too slow for synchronous execution, move the evaluation to the Edge Function (cron trigger epic) and use Supabase's built-in parallelism. The service interface does not change, only the execution context.
If the push notification service fails (FCM outage, invalid device token) during dispatch, the in-app notification may already be persisted but the push is silently lost. Inconsistent state makes it impossible to report accurate delivery status.
Mitigation & Contingency
Mitigation: Implement push dispatch and in-app persistence as separate operations with independent error handling. Record delivery_status as 'pending', 'delivered', or 'failed' on the notification_log row. Retry failed push deliveries up to 3 times with exponential backoff.
Contingency: If FCM is consistently unavailable, the in-app notification is still visible to the user, providing a degraded but functional fallback. Alert on consecutive push failures via the cron trigger's error logging.