Define ActivityType domain model and error types
epic-activity-type-configuration-foundation-task-004 — Create the immutable ActivityType Dart class with all fields matching the database schema. Define typed domain errors (ActivityTypeNotFound, ActivityTypeFetchFailure, ActivityTypePermissionDenied) as sealed classes or enums for exhaustive error handling downstream.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 1 - 540 tasks
Can start after Tier 0 completes
Implementation Notes
Place the domain model in lib/domain/activity_type/ to keep it framework-agnostic. Prefer Dart sealed classes (Dart 3+) over abstract classes for ActivityTypeError — sealed gives exhaustive switch checking for free. Pattern: `sealed class ActivityTypeError {}` with `final class ActivityTypeNotFound extends ActivityTypeError { final String id; ... }`.
For the immutable model, consider using the 'equatable' or 'freezed' package if the rest of the codebase already uses one of them — check existing models before adding a new dependency. If freezed is in use, use @freezed for ActivityType and @freezed with unionValues for ActivityTypeError. fromJson should delegate metadata parsing to ActivityTypeMetadata.fromJson() which will be defined in task-006; add a TODO comment referencing that task if metadata model is not yet available.
Testing Requirements
Unit tests with flutter_test: (1) fromJson round-trip — serialise and deserialise a known JSON fixture and assert all fields are equal; (2) fromJson with null metadata field — assert a valid default ActivityTypeMetadata is returned; (3) fromJson with missing required fields — assert a descriptive FormatException is thrown; (4) copyWith — verify only the specified field changes; (5) sealed class exhaustiveness — write a switch on ActivityTypeError in a test helper and confirm the Dart analyser flags a missing case if a new subtype is added without updating the switch. No integration or e2e tests required for pure domain models.
The JSONB metadata column has no enforced schema at the database level. If the Dart model and the stored JSON diverge (e.g., a field is renamed or a new required flag is added without a migration), the metadata resolver will silently return null or throw at parse time, breaking conditional wizard logic for all organisations.
Mitigation & Contingency
Mitigation: Define a versioned Dart Freezed model for ActivityTypeMetadata and add a Supabase check constraint or trigger that validates the JSONB structure on write. Document the canonical metadata schema in a shared constants file and require schema review for any metadata field additions.
Contingency: Implement a lenient parse path in ActivityTypeMetadataResolver that returns safe defaults for missing fields and logs a structured warning to Supabase edge logs, allowing the app to degrade gracefully rather than crash.
If RLS policies on the activity_types table are misconfigured, a coordinator from one organisation could read or mutate activity types belonging to another organisation, violating data isolation guarantees required by all three client organisations.
Mitigation & Contingency
Mitigation: Write integration tests against the Supabase local emulator that explicitly assert cross-org isolation: a token scoped to org A must receive zero rows when querying org B activity types, and upsert attempts must return permission-denied errors.
Contingency: Apply an emergency RLS policy patch via Supabase dashboard without a code deploy. Audit all activity_type rows for cross-org contamination and restore from backup if any data leakage is confirmed.
If the cache invalidation call in ActivityTypeService is not reliably triggered after an admin creates, edits, or archives an activity type, peer mentors on the same device will see stale data in the registration wizard until the next app restart, leading to confusion and potential misregistrations.
Mitigation & Contingency
Mitigation: Enforce a strict pattern: ActivityTypeService always calls cacheProvider.invalidate() inside the same try block as the successful Supabase mutation, before returning to the caller. Write a widget test that verifies the cache notifier emits an updated list after a service mutation.
Contingency: Add a background Supabase Realtime subscription on the activity_types table that triggers cache invalidation automatically, providing an independent safety net independent of the service call path.