Implement sheet dismissal and cancellation handling
epic-receipt-capture-and-attachment-core-logic-task-011 — Handle all ReceiptCameraSheet dismissal scenarios: user swipes down, taps backdrop, presses system back button, or taps Cancel. On dismissal without selection return null to the calling widget without triggering upload. Prevent accidental dismissal during active upload with a confirmation dialog. Integrate with WillPopScope for Android back button interception.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 3 - 413 tasks
Can start after Tier 2 completes
Implementation Notes
Check Flutter version targeting: use PopScope with canPop and onPopInvoked for Flutter 3.16+ — WillPopScope is deprecated. The upload state should be read from ReceiptAttachmentService's stream (or Riverpod/BLoC state) — do not duplicate state within this widget. The confirmation dialog should be a simple AlertDialog rather than a custom bottom sheet to avoid nested modal complexity. Ensure that barrierDismissible: false is set on showModalBottomSheet when upload is in progress so the user cannot bypass the confirmation by tapping the backdrop — this requires dynamically controlling the sheet's barrier behaviour, which may require replacing the standard sheet with a custom overlay if Flutter's showModalBottomSheet does not support dynamic barrierDismissible.
Consider using a StatefulWidget with an isUploading flag synced from the service stream. Clean cancellation: call ReceiptAttachmentService.cancelUpload() before Navigator.pop() to guarantee no orphaned Supabase Storage objects.
Testing Requirements
Widget tests: verify swipe-down returns null; verify backdrop tap returns null; verify Cancel button returns null; verify back button returns null; verify confirmation dialog appears when upload is in progress; verify 'Stay' resumes upload state; verify 'Cancel upload' calls ReceiptAttachmentService.cancelUpload() and returns null. Use mocktail to mock ReceiptAttachmentService and control the upload state stream. Test both PopScope (Flutter 3.16+) and WillPopScope fallback if supporting older Flutter versions.
Non-blocking upload creates a race condition: if the claim record is submitted and saved before the upload completes, the storage path may never be written to the claim_receipts table, leaving the claim with a missing receipt that was nonetheless required.
Mitigation & Contingency
Mitigation: Design the attachment service to queue a completion callback that writes the storage path to the claim record upon upload completion, even after the claim form has submitted. Use a local task queue with persistence to survive app backgrounding. Test the race condition explicitly with simulated slow uploads.
Contingency: If the async path association proves unreliable, fall back to blocking upload before claim submission with a clear progress indicator, accepting the UX trade-off in exchange for data integrity.
The offline capture requirement (cache locally, sync when connected) significantly increases state management complexity. If the offline queue is not durable, receipts captured without connectivity may be lost when the app is killed, causing claim submission failures users are not aware of.
Mitigation & Contingency
Mitigation: Persist the offline upload queue to local storage (e.g., Hive or SQLite) on every state transition. Implement background sync using WorkManager (Android) and BGTaskScheduler (iOS). Scope the initial delivery to online-only flow if offline sync cannot be adequately tested before release.
Contingency: Ship without offline support in the first release, displaying a clear 'Upload requires connection' message. Add offline sync as a follow-on task once the core online flow is validated in production.
The inline bottom sheet presentation within a multi-step wizard can conflict with existing modal navigation and back-button handling, particularly if the expense wizard itself uses nested navigation or custom route management.
Mitigation & Contingency
Mitigation: Review the expense wizard navigation architecture before implementation. Use showModalBottomSheet with barrier dismissal disabled to prevent accidental dismissal. Coordinate with the expense wizard team on modal stacking behavior and ensure the camera sheet does not interfere with wizard step transitions.
Contingency: If modal stacking causes navigation issues, present the camera sheet as a full-screen dialog using PageRouteBuilder with a transparent barrier, preserving wizard state via the existing Bloc while still appearing inline.