Plain Language Error Display widget
epic-cognitive-accessibility-foundation-task-013 — Implement the PlainLanguageErrorDisplay Flutter widget that renders error messages from the ErrorMessageRegistry via the PlainLanguageContentService. Displays a short plain-language message, a one-sentence actionable instruction, and an optional 'Get help' link. Integrates with the live region announcer for screen reader announcements. Replaces all raw error code displays throughout the app. Styled using accessibility design tokens for contrast compliance.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 2 - 518 tasks
Can start after Tier 1 completes
Implementation Notes
Make this widget a pure presentation component — it receives resolved content from PlainLanguageContentService but does not call the service itself. Keep the service call in the parent (screen or BLoC) so the widget remains easy to test in isolation. The live region pattern in Flutter requires wrapping in a Semantics widget with liveRegion: true AND ensuring the widget is inserted (not just updated) each time an error appears — if the parent conditionally shows/hides the widget, insertion triggers the announcement. If errors update in-place (same widget, new content), use a UniqueKey to force a full widget replacement and re-trigger the live region.
Avoid using SnackBar for errors throughout the app — SnackBars are not reliably accessible on all screen readers. Use ONLY PlainLanguageErrorDisplay for user-facing errors going forward.
Testing Requirements
Write flutter_test widget tests covering: (1) known errorCode renders correct headline, instruction, and help link, (2) unknown errorCode renders generic fallback message, (3) live region Semantics node is present with liveRegion: true when widget is in the tree, (4) 'Get help' link is absent when helpUrl is null, (5) onHelpTap callback fires on tap, (6) minimum touch target size of 44dp verified via widget bounds, (7) fallback message does not contain the raw errorCode string. Run accessibility checks using flutter_test's SemanticsController. Include a golden test snapshot of the error widget with a known error code to catch unintended visual regressions. Target 100% line coverage on the widget file.
The error message registry and help content registry both depend on bundled JSON assets loaded at startup. If asset loading fails silently (e.g. malformed JSON, missing pubspec asset declaration), the entire plain-language layer falls back to empty strings or raw error codes, breaking the accessibility guarantee app-wide.
Mitigation & Contingency
Mitigation: Implement eager validation of both assets during app initialisation with an assertion failure in debug mode and a structured error log in release mode. Add integration tests that verify asset loading in the Flutter test harness on every CI run.
Contingency: Ship a hardcoded minimum-viable fallback message set directly in Dart code so the app always has at least a safe generic message, preventing a blank or code-only error surface.
The AccessibilityDesignTokenEnforcer relies on dart_code_metrics custom lint rules. If the lint toolchain is not already configured in the project's CI pipeline, integrating a new linting plugin may cause unexpected build failures or require significant CI configuration work beyond the estimated scope.
Mitigation & Contingency
Mitigation: Audit the existing dart_code_metrics configuration in the project before starting implementation. Scope the lint rules to a separate Dart package that can be integrated incrementally, starting with the most critical rule (hard-coded colors) and adding others in subsequent iterations.
Contingency: Fall back to Flutter test-level assertions (using the cognitive-accessibility-audit utility) to catch violations in CI if the lint plugin integration is delayed, preserving enforcement coverage without blocking the epic.
WizardDraftRepository must choose between shared_preferences and Hive for local persistence. Choosing the wrong store for the data volume (e.g. shared_preferences for complex nested wizard state) can lead to serialisation bugs or performance degradation, particularly on lower-end Android devices used by some NHF members.
Mitigation & Contingency
Mitigation: Define a clean repository interface first and implement shared_preferences as the initial backend. Profile serialisation round-trip time with a realistic wizard state payload (≈10 fields) before committing to either store.
Contingency: Swap the persistence backend behind the repository interface without touching wizard UI code, which is possible precisely because the repository abstraction isolates the storage detail.
The AccessibilityDesignTokenEnforcer scope could expand significantly if a large portion of existing widgets use hard-coded values. Discovering widespread violations during this epic would force either a major refactor or a decision to exclude legacy components, potentially reducing the enforcer's coverage and value.
Mitigation & Contingency
Mitigation: Run a preliminary audit of existing widgets using a simple grep for hard-coded hex colors and raw pixel values before implementation begins. Use the results to set a realistic remediation boundary for this epic and log all out-of-scope violations as tracked tech-debt items.
Contingency: Scope the enforcer to new and modified components only (via file-path filters in dart_code_metrics config), shipping a partial but immediately valuable coverage rather than blocking the epic on full-codebase remediation.