Integrate ErrorMessageRegistry with PlainLanguageErrorDisplay
epic-cognitive-accessibility-wizard-ui-task-006 — Connect PlainLanguageErrorDisplay to the ErrorMessageRegistry (from the foundation epic) so that error codes are resolved to structured {headline, action} message objects. The widget should accept an error code string, look it up in the registry, and fall back to a generic plain-language message if the code is not found. Ensure the registry lookup is synchronous to avoid display delay.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 1 - 540 tasks
Can start after Tier 0 completes
Implementation Notes
Inject the registry via constructor to keep the widget testable: `PlainLanguageErrorDisplay({required String? errorCode, ErrorMessageRegistry? registry})` — default the registry parameter to `ErrorMessageRegistry.instance` inside the constructor body so production code is zero-boilerplate. Define a private const `_fallback = ErrorMessage(headline: '...', action: '...')` at the top of the file.
Resolve inside `build()` using a local variable (`final msg = (widget.errorCode != null ? registry.resolve(widget.errorCode!) : null) ?? _fallback`) so the resolution is purely functional with no side effects. Avoid `initState`/`didChangeDependencies` for the lookup — keeping it in `build()` means hot-reload and widget tree reconstruction work correctly without stale state.
If ErrorMessageRegistry is a singleton built on a `const Map`, the lookup is guaranteed O(1) with no locking concerns on the UI thread.
Testing Requirements
Write unit tests for the registry resolution logic (pure Dart, no Flutter widgets): (1) known code returns correct {headline, action} object, (2) unknown code returns the fallback object, (3) null/empty code returns null without throwing. Write widget tests using a stub registry: verify that with a known code the rendered Text widgets show the correct headline and action strings; verify that with an unknown code the fallback strings are rendered; verify that with a null code the widget tree is empty. Confirm no extra rebuild occurs by spying on build call count. All tests must pass with `flutter test` in CI.
The WizardStateManager BLoC must guarantee that step transitions only occur on explicit user action, never automatically. Subtle reactive patterns in Bloc (e.g. stream listeners triggering add() calls) could inadvertently auto-advance the wizard, violating the core cognitive accessibility rule and creating a regression that is difficult to detect without dedicated tests.
Mitigation & Contingency
Mitigation: Write a dedicated unit test that subscribes to the BLoC stream and asserts no StepChanged event is emitted for 5 seconds after a state update, without an explicit user-sourced event being dispatched. Make this test part of the CI gate for the WizardStateManager.
Contingency: If an auto-advance regression is discovered post-integration, introduce a mandatory UserActionToken parameter on all step-transition events so the BLoC can structurally refuse transitions that do not originate from a user gesture handler.
The ConfirmBeforeSubmitScreen requires deep-linking back to specific wizard steps for corrections. Implementing bidirectional navigation within a multi-step wizard while preserving all previously entered state is architecturally non-trivial and may conflict with the existing StatefulShellRoute navigation setup described in the app architecture.
Mitigation & Contingency
Mitigation: Design the ConfirmBeforeSubmitScreen's back-navigation links to dispatch a GoToStep event on the WizardStateManager rather than using GoRouter's pop() chain. This keeps navigation state entirely in the BLoC and avoids coupling to the router's stack semantics.
Contingency: If BLoC-driven step navigation proves incompatible with the router, implement the correction flow as a dedicated sub-route that pre-populates its form from the WizardStateManager's current draft, then merges the edited field back into the draft on completion before returning to the confirm screen.
The CognitiveAccessibilityAudit utility must inspect live widget trees for violations such as icon-only buttons. Flutter's widget tree inspection APIs are available in test mode but have limitations in identifying semantic intent (e.g. distinguishing a decorative icon from a navigation button). False negatives could give a false sense of compliance.
Mitigation & Contingency
Mitigation: Augment the audit with a convention-based approach: require all navigation buttons to use a named wrapper widget (e.g. LabelledNavigationButton) that the audit can detect by type, rather than relying solely on widget-tree semantics analysis.
Contingency: If widget-tree detection proves insufficiently reliable, scope the CognitiveAccessibilityAudit to route-configuration analysis (verifying back navigation availability per route) and static analysis of wizard step count definitions via the CognitiveLoadRuleEngine, which provides deterministic results.
The InlineContextualHelpWidget sources content from a bundled JSON asset via the HelpContentRegistry. If help texts are missing for newly added screens or fields (a likely scenario as the 61-feature app grows), the widget silently shows nothing, degrading the accessibility experience without any visible failure.
Mitigation & Contingency
Mitigation: Integrate a CognitiveAccessibilityAudit check that verifies every registered (screenId, fieldId) pair that requests help has a corresponding entry in the HelpContentRegistry bundle. Run this check in CI as part of the audit report.
Contingency: Add a debug-mode overlay that highlights fields with missing help entries using a visible warning indicator, making coverage gaps immediately obvious to developers during local development before they reach CI.