Implement keyboard navigation for map overlay controls
epic-geographic-peer-mentor-map-ui-accessibility-task-011 — Add full keyboard navigation to all overlay controls within MapViewScreen: filter panel toggle button, view toggle FAB, and zoom controls. Implement a logical tab order that moves through controls without entering the non-semantic map canvas. Add keyboard shortcuts documentation in the screen's semantic description. Verify with Flutter integration test that all interactive elements are reachable via keyboard traversal.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 4 - 323 tasks
Can start after Tier 3 completes
Implementation Notes
Wrap the map canvas in an ExcludeSemantics widget and a FocusTraversalGroup with policy: NeverFocusedFocusTraversalPolicy so keyboard users skip it entirely. Use FocusTraversalGroup with OrderedTraversalPolicy on the overlay controls stack to enforce tab order independent of widget tree position. Manage filter panel focus with a FocusNode: call FocusScope.of(context).requestFocus(firstPanelFocusNode) when the panel opens, and call filterToggleFocusNode.requestFocus() when it closes. Add the keyboard hint to MapViewScreen via Semantics(label: '...', child: ...) at the scaffold level, not on individual buttons.
Ensure all focusable widgets have a visible focusDecoration — Flutter's default focus highlight may be invisible on dark backgrounds, so use a Theme override or custom focus indicator using FocusHighlight.
Testing Requirements
Write a Flutter integration test using tester.sendKeyEvent(LogicalKeyboardKey.tab) to cycle through all controls and assert each receives focus in the expected order. Assert that the map canvas widget is not in the focus traversal path using FocusTraversalGroup with the policy set to skip the canvas subtree. Test focus restoration: open filter panel, assert focus is inside panel; close panel, assert focus returns to filter toggle button. Run flutter_test semantics dump to confirm no unlabelled focusable nodes.
Test on both physical keyboard and simulated switch access.
Flutter's map canvas (flutter_map) does not natively support semantic focus traversal for screen readers, meaning map markers may be entirely invisible to VoiceOver/TalkBack users. If the accessible list fallback is not treated as a first-class view, screen reader users will have no access to the feature.
Mitigation & Contingency
Mitigation: From sprint 1, treat mentor-list-fallback as a fully featured primary view, not an afterthought. Implement and test it in parallel with the map canvas. Make the view-toggle-button keyboard focusable and announced on every screen state. Conduct VoiceOver testing on device before submitting each PR touching UI components.
Contingency: If map canvas accessibility cannot be achieved for marker focus traversal, make the view-toggle-button the default focus target on screen load for VoiceOver users (detected via screen-reader-detection-service) so they are immediately directed to the list fallback without needing to discover the toggle.
The mentor-info-popup must occupy no more than 40% of visible map area on small screens. On devices with screen heights under 667px (iPhone SE), overlapping with the filter panel or obscuring most of the map could severely degrade usability.
Mitigation & Contingency
Mitigation: Implement the popup as a bottom sheet capped at 40% of screen height with a ScrollView for overflow content. Test on iPhone SE (375x667pt) and the smallest commonly used Android form factor in the device lab. Define max-height as a percentage constant in location-privacy-config or design tokens.
Contingency: If the popup cannot fit all required fields within 40% height on smallest targets, truncate assigned contact count and certification badge to icons-only in the compact view, with a 'View Profile' button always visible at the bottom of the popup regardless of scroll position.
Filter state must remain perfectly synchronised between the map view and the list fallback. If the filter panel emits state that is not consumed identically by both views, coordinators switching between views will see inconsistent mentor sets, eroding trust in the feature.
Mitigation & Contingency
Mitigation: Store active filter criteria in a single shared Riverpod provider owned by the map-view-screen and consumed by both map-marker-widget (via mentor-location-service) and mentor-list-fallback. Write integration tests that apply a filter, switch views, and assert identical mentor counts in both views.
Contingency: If filter sync proves brittle, simplify to a single filter state object passed explicitly as a constructor argument to both views on each rebuild, eliminating indirect state sharing.