DuplicateResolutionHandler — merge resolution path
epic-duplicate-activity-detection-ui-task-005 — Implement the merge resolution path in DuplicateResolutionHandler. When the user selects Merge, the handler must apply draft corrections onto the existing duplicate record via an update operation, discard the draft, and close the bottom sheet, presenting a confirmation to the user that the existing record was updated.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 4 - 323 tasks
Can start after Tier 3 completes
Implementation Notes
Implement merge() as a separate method on DuplicateResolutionHandler. Build a MergePayloadBuilder utility that diffs ActivityDraft against the existing Activity and returns only the mutable changed fields. Define a MERGEABLE_FIELDS constant (e.g., ['date', 'duration_minutes', 'activity_type_id', 'summary']) to act as the whitelist — never merge id, organization_id, peer_mentor_id, contact_id, or created_at. Use Supabase's .update(payload).eq('id', existingId) — never use upsert for merge as it can silently create a record if the id is not found.
Wrap in a transaction if Supabase Edge Function is available; otherwise accept last-write-wins semantics with the understanding that coordinators can correct records.
Testing Requirements
Write unit tests for DuplicateResolutionHandler.merge() covering: (1) only differing fields are included in the update payload; (2) organization_id and contact_id are not overwritten; (3) duplicate_reviewed = true is set on the payload; (4) on success, ActivityMergeSuccess emitted; (5) on failure, ActivityMergeError emitted. Write integration tests against Supabase test project: (6) existing record is updated with draft fields; (7) no new record is inserted; (8) RLS blocks merging into another user's record. Test field-diff logic exhaustively with equal fields, all-different fields, and partially different fields.
The merge resolution path requires identifying which fields from the draft differ from the existing record, applying those differences to the existing record, and cancelling the draft — all as an atomic operation. Partial failures (e.g., update succeeds but draft cancellation fails) could leave the system in an inconsistent state.
Mitigation & Contingency
Mitigation: Implement the merge path as a Supabase RPC transaction that updates the existing record and soft-deletes the draft in a single atomic call. The DuplicateResolutionHandler should never attempt field-level merge at the application layer.
Contingency: If the atomic RPC approach proves too complex for the initial release, simplify the merge path to: mark existing record as the canonical record and cancel the new submission without field merging, displaying a message to the user to manually verify the existing record's fields. Log a follow-up ticket for full field-merge in a later sprint.
The DuplicateWarningBottomSheet must intercept the activity wizard's save action without disrupting the wizard's existing navigation stack. If the bottom sheet is implemented as a separate route rather than an overlay, back navigation could break the wizard's step state.
Mitigation & Contingency
Mitigation: Use a `showModalBottomSheet` overlay pattern so the bottom sheet sits above the wizard route without pushing a new route onto the Navigator stack. The wizard's CuBit/BLoC retains all draft state while the sheet is visible. Test this integration with the existing activity-registration-cubit before merging.
Contingency: If the overlay approach causes Z-order or focus issues with the wizard's keyboard-aware layout, route the duplicate check result back to the wizard as a state event (DuplicateDetected), and let the wizard render a local inline warning banner instead of a bottom sheet.
The bottom sheet and comparison panel involve complex layouts with multiple interactive elements. Screen reader users (particularly relevant for Blindeforbundet) may struggle with the side-by-side comparison layout if semantics are not carefully ordered.
Mitigation & Contingency
Mitigation: Design the comparison panel with a single-column semantic order (read record A fully, then record B fully) regardless of visual layout. Use Flutter's `Semantics` widget with `sortKey` to enforce correct traversal order. Test with TalkBack and VoiceOver against the WCAG 2.2 AA reading order criteria.
Contingency: If side-by-side layout cannot achieve acceptable screen reader ordering, switch to a stacked tab layout (Tab A / Tab B) for the comparison panel that is semantically simple even if less visually immediate for sighted users.