Add WCAG 2.2 AA semantics to PickerUI with upload progress announcements
epic-document-attachments-ui-task-010 — Apply full WCAG 2.2 AA accessibility to AttachmentPickerUI: semantic labels for source selection options (camera roll, file system), live region announcements for upload progress percentage and completion confirmation, plain-language error messages for MIME type rejection and limit exceeded, minimum 44x44 pt touch targets throughout, and screen reader navigation between the preview rows.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 2 - 518 tasks
Can start after Tier 1 completes
Implementation Notes
The upload progress announcement throttling is the trickiest part — maintain a _lastAnnouncedMilestone int in the BLoC and only call SemanticsService.announce when the current milestone bucket (floor(percent / 25) * 25) is greater than _lastAnnouncedMilestone. This prevents announcement spam on fast connections while still giving meaningful progress feedback. For screen reader navigation order in the preview list, use MergeSemantics or an explicit Semantics traversal order (via sortKey) to ensure VoiceOver reads thumbnail → filename → size → remove button in that order per row. Given this project's strong accessibility mandate (Blindeforbundet users with screen readers, NHF cognitive accessibility requirements), add a comment block above the Semantics annotations explaining the intent so future developers do not inadvertently remove them.
Testing Requirements
Widget tests using flutter_test: (1) render picker and assert both source option semantic labels are present, (2) inject two PendingAttachment items and assert each preview row has the expected semantic label, (3) simulate a MIME rejection event from the BLoC and assert SemanticsService.announce was called with the rejection message, (4) simulate upload progress events at 25%, 50%, 75%, 100% and assert announce is called exactly 4 times with the correct messages, (5) simulate limit-exceeded state and assert the error message announce fires once. Use a MockSemanticsService. Manual TalkBack (Android) and VoiceOver (iOS) tests on TestFlight to confirm all announcements are intelligible and navigation order is logical.
Flutter does not include a first-party PDF renderer. Third-party packages (e.g., flutter_pdfview, syncfusion_flutter_pdf) have inconsistent accessibility support, may not honour dynamic type scaling, and can introduce large binary size increases. Choosing the wrong package late in development risks rework or an inaccessible PDF experience for Blindeforbundet users.
Mitigation & Contingency
Mitigation: Evaluate and spike two PDF rendering packages (flutter_pdfview and pdfx) in the first task of this epic before committing to implementation. Criteria: VoiceOver compatibility, dynamic type support, APK/IPA size delta, and licence. Document the decision in an ADR.
Contingency: If no package meets accessibility requirements, fall back to opening PDFs in the system browser via url_launcher, which inherits the OS's accessible PDF viewer. Display a clear 'Opening in external viewer' message to set user expectation.
Flutter's Semantics API for live region announcements (analogous to aria-live) has known gaps on Android for dynamic content updates. Upload progress announcements required by the accessibility user story may not fire reliably on Android devices used by HLF and NHF members.
Mitigation & Contingency
Mitigation: Use SemanticsService.announce() for imperative announcements at each upload state transition rather than relying on declarative Semantics widget tree updates. Test on a physical Android device with TalkBack enabled during development, not only on iOS with VoiceOver.
Contingency: If SemanticsService.announce() proves unreliable, implement a persistent accessible status banner at the top of the screen that reflects the current upload state as plain text, satisfying the WCAG success criterion through a visual + programmatic mechanism.
iOS and Android file picker behaviour diverges significantly: MIME type filtering works reliably on Android but is advisory on iOS (users can still navigate to and select non-compliant files via the Files app). This could allow unsupported file types to reach the upload service, causing validation failures with a confusing user experience.
Mitigation & Contingency
Mitigation: Rely on the AttachmentUploadService (Epic 2) as the authoritative MIME validation gate, regardless of platform. In the UI, re-validate the picked file's extension/MIME after selection and show an inline plain-language error ('Only PDF, JPEG, and PNG files are supported') before even calling the service.
Contingency: If users consistently hit the error due to iOS file picker limitations, add a user-facing help tooltip on the picker sheet explaining the supported file types, reducing support volume while the underlying OS limitation persists.
WCAG 2.2 AA compliance for three new interactive components (picker, grid, modal) with file system integration, role-gated actions, and live regions is a significant accessibility surface area. An incomplete audit before release could result in the feature being unusable for Blindeforbundet screen reader users at launch.
Mitigation & Contingency
Mitigation: Allocate a dedicated accessibility audit task at the end of the epic using the accessibility-test-harness (619) and wcag-compliance-checker (620) components already in the project. Include at least one manual test session on a physical device with VoiceOver enabled. Fail the epic's definition of done if any WCAG 2.2 AA violation remains open.
Contingency: If critical accessibility issues are found late, gate the feature behind the org-level attachments_enabled feature flag and only enable it for NHF (the requesting org) after a targeted fix cycle, rather than delaying the release for all organisations.