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name ui-and-accessibility
description Load BEFORE touching any file under lib/screens/, lib/widgets/, lib/main.dart, or lib/app_theme.dart — any visual change, new screen, restyle, "make this look nicer," redesign, new widget, colour/theme change, or accessibility fix. Triggers — "redesign the drinks screen", "add a badge to the drink card", "restyle this", "add Semantics", "make it accessible", "update the golden", "change the bottom nav", "add a route", "per-festival theme", "My Festival status badges". Provides the UI-change discipline that prevents this project's costliest historical failure mode (sweeping redesigns), a shared-widget reuse table, the WCAG 2.1 AA Semantics catalogue, the screen patterns that must never regress (festival-flash guard, four-signal loading/error UI, navigateToRoute), and My Festival's visual-design constraints.

UI and Accessibility

This skill has two jobs, in priority order:

  1. Stop UI changes from becoming redesigns. This is not a style preference — it is the single costliest failure mode in this project's history (maintainer-confirmed).
  2. Give you the accessibility and widget-pattern catalogue so new UI meets the bar this project already holds, without re-deriving it from scratch.

If you are only changing lib/domain/, lib/providers/, or lib/services/ with no visible UI change, see skill architecture-contract instead — this skill does not apply. If you're only fixing/writing tests, see validation-and-qa. If you're implementing the My Festival campaign end-to-end, see my-festival-campaign for sequencing — come back here for the visual/accessibility rules it must follow.

Part 1 — UI-change discipline (read this first, every time)

Why this section exists

The project's principal engineer built this app largely solo, now with AI agents doing most of the typing. A sweeping visual redesign — restyle and restructure several screens in one pass — produces a diff too large for one human to review carefully, and too large for an agent to verify against the accessibility bar without missing something. Past redesigns cost more engineering time than any other category of change in this repo's history. The rules below exist because that failure mode is expensive and it has already happened.

The hard rules

  1. One widget or one screen per PR. Do not restyle DrinksScreen and DrinkCard and FestivalHeader in the same change. If a task seems to need all three, split it into sequential PRs — each independently reviewable and revertible.

  2. Restyle OR restructure — never both in the same change.

    • Restyle = colours, spacing, typography, icons, chip shapes — the widget tree shape is unchanged.
    • Restructure = changing which widgets exist, how they nest, or what data flows into them.
    • Mixing the two means a visual regression and a logic regression look identical in the diff — you cannot git revert one without the other, and a reviewer cannot separate "this looks different" from "this broke."

  3. Never rename or move a route path. URLs are a public contract — see skill change-control for the full unwritten-rules list. Concretely for UI work: the "My Festival" rename (issue #414) renames the nav label and icon, not the route. The route stays /:festivalId/favorites (lib/router.dart, MyFestivalScreen class in lib/screens/my_festival_screen.dart) even though the tab text changes to "My Festival." A visual/branding rename is never a licence to touch router.dart path strings.

  4. Prefer extending an existing widget over creating a parallel one. Before writing a new widget, check the reuse table below — this project has a deliberately small shared-component set (the identity hero panels DrinkHeroPanel/BreweryHeroPanel/StyleHeroPanel with their shared FactsStrip/FactCell, InfoChip, SectionHeader, buildOverflowMenu, the filter sheets). A second widget that does 90% of what an existing one does is scope creep and a maintenance burden for a solo maintainer.

  5. Every visual change updates goldens DELIBERATELY — never blind-regenerate. Run goldens:update scoped to the relevant _screenshot_test.dart file, then open the resulting PNG and look at it — confirm the pixel diff is the change you intended and nothing else moved. Do not run a bare goldens:update with no file argument as a reflex "fix the failing test" move; that regenerates every golden and silently launders any unintended visual drift into the baseline. Golden inventory, exact commands, and the full update protocol: skill validation-and-qa §3.5.

  6. Keep the shell/transition structure intact. router.dart nests two ShellRoutes: an outer one wrapping every route in ProviderInitializer (lib/main.dart), and an inner one wrapping only /:festivalId and /:festivalId/favorites in BeerFestivalHome (adds the bottom NavigationBar). Both of those routes use NoTransitionPage deliberately — switching tabs should not animate like a page push. Do not add page transitions to these two routes, and do not move a route between the outer and inner shell without checking whether it needs the bottom nav (detail routes — drink/brewery/style/info — deliberately sit outside the inner shell so they get no bottom nav, per docs/code/ui-components.md).

  7. Check both light and dark themes before calling a visual change done. lib/app_theme.dart:buildAppTheme(Brightness) branches on brightness for primary, AppBarTheme, and navigationBarTheme.indicatorColor — a colour that looks fine in light mode can have broken contrast in dark mode. Two of the four golden tests exist specifically to catch this (style_screen_with_description_dark.png / _light.png).

A worked example of the rule in action

Adding a status badge to DrinkCard for My Festival (planned, see Part 6) is a restyle — it adds a small icon/badge to an existing widget without changing what the card contains or how it's laid out elsewhere. That is one PR, scoped to lib/widgets/drink_card.dart (+ its test), with goldens reviewed if DrinkDetailScreen's card rendering is affected. It is explicitly not a licence to also reflow the card's internal Row/Column structure, change its elevation, or touch drinks_screen.dart's list layout in the same PR.

Part 2 — Widget standards

Verified against docs/code/widget-standards.md and the actual widget files under lib/widgets/ on 2026-07-02.

Checklist (every new/changed widget)

  • const constructor, const used wherever the compiler allows it
  • Single quotes for string literals
  • child/children last among named parameters
  • final for local variables
  • Tappable elements have a Key findable via find.byKey(const ValueKey('...')) in tests — e.g. lib/screens/drinks_screen.dart:356 and lib/screens/my_festival_screen.dart:70 both key drink-card list items on ValueKey(drink.id)
  • Content text (drink name, brewery, notes) uses SelectableText, not Text — UI labels/nav/button text stay as plain Text (docs/code/widget-standards.md); see lib/widgets/drink_hero_panel.dart (the name and "About this drink" body) for the pattern
  • Semantics wraps only the interactive element, not a whole decorative row (see Part 3)
  • Text with unbounded width has explicit overflow/maxLines

Shared-component reuse table

Check this before writing a new widget. All paths relative to lib/widgets/ unless noted.

Need Use File Notes
Identity hero card at the top of a detail screen (name, key facts, "about" notes) DrinkHeroPanel / BreweryHeroPanel / StyleHeroPanel drink_hero_panel.dart / brewery_hero_panel.dart / style_hero_panel.dart Each is a category-edged Card (CategoryColorHelper.getAccentColor) with the entity name, a shared FactsStrip of FactCells, and the entity's own "about" content inside the same card under a divider. Replaced the old filled-block HeroInfoCard (rejected — see docs/code/design-language.md §2)
Divided strip of "key facts" (centred value over an uppercase label) inside a hero FactsStrip + FactCell facts_strip.dart FactsStrip owns the top/bottom/left dividers; a FactCell becomes a navigation button when given onTap + semanticLabel
Small metadata pill (style, dispense, bar location) InfoChip info_chip.dart Optional onTap makes it a Semantics(button: true) link
Section title with underline on a detail screen SectionHeader section_header.dart showSeparator toggles the underline
Sticky bottom row of actions (tasting log, rate, favourite, share) BottomActionBar + ActionButton bottom_action_bar.dart Currently unused — no screen wires it up (the drink detail screen uses a FAB + YourTakeCard instead). Available, but check it still fits before adopting. ActionButton.isActive drives colour + FontWeight; semanticLabel overrides the visible label for screen readers
Back-navigation header on a detail screen (drink/brewery/style) BreadcrumbBar breadcrumb_bar.dart Currently unused — detail screens use CollapsingDetailAppBar + buildHomeLeadingButton. Only the IconButton gets Semantics, never the text row — see the "BAD" example in docs/code/widget-standards.md. 28px icon → 48×48 touch target. Text segments only become tappable/underlined when a callback is provided
Three-dot menu for festival switch / settings / about buildOverflowMenu(context) overflow_menu.dart A function, not a widget class — docs/code/ui-components.md documents where to include it (Drinks, My Festival screen) and where not to (detail screens, About, modals)
Modal filter pickers (category, style, sort, visibility) showCategoryFilter / showStyleFilter / showSortOptions / showVisibilityFilter drink_filter_sheets.dart All route through the private _showSheet helper (isScrollControlled: true) and share _SheetHandle — add a new filter type by adding a sheet class + show-function here, not a bespoke showModalBottomSheet call elsewhere
Star rating display or picker StarRating star_rating.dart isEditable toggles read-only vs tap-to-rate; semantic value is always '$rating out of 5 stars'
Availability / category / rating pills on a drink card _AvailabilityChip / _RatingChip / _CategoryChip / _StyleChip drink_card.dart Private to drink_card.dart — extend DrinkCard itself rather than exporting these

If your need isn't in this table and isn't a one-off, check the sibling widget files anyway (drink_list_section.dart, drinks_filter_controls.dart, festival_banner.dart, festival_header.dart, festival_menu_sheets.dart, availability_badge.dart, environment_badge.dart) before writing something new — this project keeps its component set deliberately small (rule 4 above).

Part 3 — Accessibility catalogue (WCAG 2.1 AA)

This project treats accessibility as mandatory, not optional (AGENTS.md, docs/code/accessibility.md). Standards targeted: WCAG 2.1 Level AA, ADA, Section 508 — these are the bar the code is held to, not an audited compliance claim; never state "WCAG compliant" externally (see skill docs-and-writing §8 on claim discipline).

High-priority files (touch these carefully; each already has Semantics coverage to preserve)

lib/widgets/drink_card.dart, lib/screens/drinks_screen.dart, lib/screens/festival_info_screen.dart, lib/main.dart, lib/widgets/star_rating.dart, lib/widgets/bottom_action_bar.dart, lib/widgets/breadcrumb_bar.dart, lib/widgets/overflow_menu.dart, lib/widgets/info_chip.dart, lib/widgets/festival_menu_sheets.dart, lib/widgets/environment_badge.dart, lib/screens/about_screen.dart, lib/screens/drink_detail_screen.dart.

Verified snippet patterns

Toggle button (favourite / bookmark) — label changes with state, toggled carries the on/off state to assistive tech:

Semantics(
  label: isFavourite ? 'Remove from favourites' : 'Add to favourites',
  button: true,
  toggled: isFavourite,
  hint: 'Double tap to toggle',
  child: IconButton(
    icon: Icon(isFavourite ? Icons.favorite : Icons.favorite_border),
    onPressed: () => toggleFavorite(),
  ),
)

Filter chip — value announces selection state independently of the visible chip:

Semantics(
  label: 'Filter by $styleName',
  value: isSelected ? 'Selected' : 'Not selected',
  button: true,
  selected: isSelected,
  child: FilterChip(
    label: Text(styleName),
    selected: isSelected,
    onSelected: (value) => _toggleStyle(styleName),
  ),
)

Tappable card / list row — one Semantics wrapper, not one per child Text:

Semantics(
  label: '${drink.name}, ${drink.abv}% ABV, by ${drink.breweryName}',
  hint: 'Double tap for details',
  button: true,
  child: InkWell(onTap: () => navigateToDetail(drink), child: DrinkCard(drink: drink)),
)

Star rating — matches the live implementation in star_rating.dart:41-61 exactly (parent announces the summary, each star is independently labelled):

Semantics(
  label: isEditable ? 'Rate this drink' : 'Rating',
  value: '$ratingValue out of 5 stars',
  hint: isEditable ? 'Tap a star to rate from 1 to 5. Tap again to clear rating.' : null,
  enabled: isEditable,
  child: Row(
    children: List.generate(5, (i) => Semantics(
      label: 'Star ${i + 1}',
      button: isEditable,
      selected: rating != null && i + 1 <= rating!,
      child: GestureDetector(/* ... */),
    )),
  ),
)

Decorative icon inside an otherwise-labelled control — wrap it in ExcludeSemantics so it isn't announced twice (see overflow_menu.dart:28):

ExcludeSemantics(child: Icon(Icons.festival, color: menuContentColor))

Rules that apply everywhere

  • Every interactive element gets a Semantics wrapper with a meaningful label describing the action, not the icon ('Add to favourites', not 'Heart icon').
  • Touch targets: 24×24 px minimum (WCAG AA); this project's icon buttons generally exceed that (BreadcrumbBar's back button is 28px icon → 48×48 effective target).
  • Colour contrast 4.5:1 for text; never rely on colour alone to convey state (relevant to My Festival badges — see Part 6).
  • Don't wrap a whole Row containing both a button and plain text in one Semantics(button: true) — only the actually-tappable part gets the wrapper (docs/code/widget-standards.md's BAD example).

The duplicate-semantics-node gotcha

Some Flutter widgets (FilledButton.icon, ElevatedButton.icon) synthesise their own semantics node from their visible text label. If you also wrap that button in an explicit Semantics(label: '...') with the same text, two nodes with that label now exist in the tree, and expect(find.bySemanticsLabel('...'), findsOneWidget) fails. Fix: use findsWidgets instead of findsOneWidget, or switch to the widget-predicate strategy. Full detail on all three semantics-testing strategies (widget predicate, rendered tree via tester.ensureSemantics(), node-properties inspection) lives in skill validation-and-qa — this skill owns what the label should be; that skill owns how to assert it in a test.

Part 4 — Screen patterns that must be preserved

These are invariants, not suggestions — each exists because of a specific, citable bug. Breaking one silently reintroduces a fixed defect.

1. Festival-flash guard (REQUIRED in any festival-scoped screen)

lib/screens/my_festival_screen.dart (first thing in MyFestivalScreen.build):

final provider = context.watch<BeerProvider>();
if (provider.currentFestival.id != festivalId) {
  return buildLoadingScaffold();
}

festivalId is the route's path parameter, not provider.currentFestival.id. This exists because _festivalScopeRedirect (lib/router.dart:24-42) defers the actual festival switch to a post-frame callback and returns null — so without this guard, the first frame after a cross-festival deep link or festival switch renders the previous festival's data for one frame (issue #397, following the broader #310 family; fixed in PR #409). Any new festival-scoped screen — including the eventual My Festival Phase-1 screen (issue #414, which explicitly says "inherit the fix from #397... build this in from day one") — must carry this guard from its first commit, not as a follow-up fix.

2. Four-signal loading/error UI

BeerProvider exposes four mutually-exclusive-by-construction signals; DrinksScreen (lib/screens/drinks_screen.dart) is the reference implementation of how each maps to UI:

Field Getter Widget Condition (verified drinks_screen.dart line)
_isLoading isLoading Full-screen CircularProgressIndicator provider.isLoading && provider.drinks.isEmpty (~263)
_isRefreshing isRefreshing LinearProgressIndicator(minHeight: 2) at top provider.isRefreshing && hasData (~251)
_refreshNotice (non-null) refreshNotice Dismissible banner provider.refreshNotice != null && hasData (~209)
_error (non-null) error Full error view + Retry provider.error != null && provider.drinks.isEmpty (~279)

_error and _refreshNotice are never both non-null at once (enforced in beer_provider.dart's _refreshDrinksFromNetwork). When adding a new screen that reads from BeerProvider, reuse this same four-branch structure — don't invent a fifth loading state or collapse two of these into one.

3. navigateToRoute + typed path builders

lib/utils/navigation_helpers.dart:237 — navigateToRoute(context, path) calls context.push(path) on every platform. It used to branch to context.go() on web (the URL bar didn't follow a push from inside a ShellRoute); GoRouter.optionURLReflectsImperativeAPIs fixed that in #470, and go was disposing the calling screen and losing its scroll. Use it for any drill-down navigation to content (drink detail, brewery, style). For root/tab navigation that replaces the stack (bottom nav taps, "go home"), call context.go() directly instead — that's a deliberate exception, not an inconsistency.

Always build paths with the typed helpers in the same file — never interpolate a raw string:

navigateToRoute(context, buildDrinkDetailPath(festivalId, category, drinkId));
navigateToRoute(context, buildBreweryPath(festivalId, breweryId));
navigateToRoute(context, buildStylePath(festivalId, style)); // lowercases + encodes

Available builders (lib/utils/navigation_helpers.dart): buildFestivalPath, buildFestivalHome, buildDrinksPath, buildFavoritesPath, buildFestivalInfoPath, buildDrinkDetailPath, buildBreweryPath, buildStylePath, buildCategoryPath. Each asserts non-empty required arguments in debug mode and URL-encodes user-provided segments.

4. Post-frame analytics in initState

Screens that log an analytics event on open must defer it past the first frame, matching lib/screens/drink_detail_screen.dart:30-37:

@override
void initState() {
  super.initState();
  WidgetsBinding.instance.addPostFrameCallback((_) {
    final provider = context.read<BeerProvider>();
    unawaited(provider.analyticsService.logDrinkViewed(drink));
  });
}

Calling context.read<BeerProvider>() directly inside initState (before the first frame) is a common source of provider-not-ready errors; the post-frame callback sidesteps it. Always unawaited(...) the log call itself — analytics must never block or fail the UI (see skill architecture-contract for the broader analytics invariant).

5. Search debounce (300ms)

lib/screens/drinks_screen.dart:23-28 debounces the search field so every keystroke doesn't re-run the full filter + analytics pipeline:

Timer? _searchDebounceTimer;
// ...
_searchDebounceTimer?.cancel();
_searchDebounceTimer = Timer(const Duration(milliseconds: 300), () {
  provider.setSearchQuery(query);
});

Cancel the timer in dispose() and on any early-exit path (e.g. clear button) — drinks_screen.dart cancels it at three call sites, not just dispose(). Reuse this exact pattern for any new free-text search field rather than inventing a new debounce mechanism.

Part 5 — Theming

lib/app_theme.dart:

  • appSeedColor = Color(0xFF2B3170) — CBF 2026 poster navy. Single hardcoded seed today; there is no per-festival or per-user theme switching in code.
  • buildAppTheme(Brightness brightness) builds ColorScheme.fromSeed(...) from that one seed, with light/dark overrides for primary (light: seed navy; dark: a lighter 0xFF8FA3E8) and for AppBarTheme/ navigationBarTheme.indicatorColor.
  • buildAppTextTheme(ColorScheme) pairs Playfair Display (display/ headline/titleLarge — the serif "poster" voice) with Nunito Sans (body/ label/titleMedium-and-below), both via google_fonts.
  • MaterialApp in lib/main.dart consumes buildAppTheme(Brightness.light) / buildAppTheme(Brightness.dark) directly; BeerProvider.themeMode controls which one is active (system/light/dark), not the seed colour.

Per-festival theming is issue #40 — OPEN, a candidate, not implemented. It proposes giving Festival a seedColor field (sourced from each year's poster palette) so the theme could shift when setFestival() is called, plus optionally a user-facing theme picker. Neither exists in code today — do not build against an assumed Festival.seedColor field. If you pick this up, start from the issue's own open questions (server-controlled vs hardcoded seed per festival; user picker vs automatic; light-only vs light+dark) rather than re-deriving them.

Part 6 — My Festival UI specifics (the live workstream)

This is the project's current highest-priority live UI work (issues #411→#415; see skill my-festival-campaign for sequencing across the whole campaign, including the non-UI cloud-sync half). This section covers only the visual/accessibility design intent, sourced from docs/planning/my-festival/vision.md (status: vision doc, dated May 2026) and issue #414 (open as of 2026-07-02).

Planned status badges on drink cards

Design intent, not yet implemented in lib/widgets/drink_card.dart:

State Badge
Want to Try Grey circle outline icon (○)
Tasted (once) Green checkmark (✓)
Tasted (multiple) Green checkmark + count badge (✓ 3×)

Design constraints (from vision.md — treat as binding once this is built)

  • Subtle, clean — badges must not clutter the card (this is a restyle constraint per Part 1: adding a badge to DrinkCard should not become an excuse to re-lay-out the card).
  • WCAG AA colour contrast on the badge itself.
  • 24×24 px minimum touch target if the badge is itself tappable.
  • Semantics label on every badge state (state-aware, following the toggle pattern in Part 3 — e.g. 'Marked as tasted, 3 times' rather than just an icon).

Rejected alternatives (do not propose these again — already litigated in vision.md)

  • Colour-coded card backgrounds per state — rejected for accessibility issues and visual clutter.
  • Opacity fade for tasted items — rejected because faded items read as "disabled" and become harder to read, which is the opposite of the intent (a tasted drink is still fully relevant information).

Section-membership + layout (informs any list/screen work, not just badges)

Per vision.md: a drink appears in Tasted whenever tastingEvents.isNotEmpty; it appears in Want to Try only when wantToTry == true AND tastingEvents.isEmpty — membership is derived from UserDrinkState, never stored as a separate flag. The planned My Festival screen (issue #414) is a single scrollable screen with two sections (Want to Try alphabetical list on top; Tasted grouped-by-day reverse-chronological timeline on bottom), separated by a visual divider, both equally reachable. Placeholder rows are required for entry.drink == null (catalogue not yet hydrated — see MyFestivalEntry.isCatalogueLoaded, lib/models/my_festival_entry.dart). This is forward-looking design intent for a not-yet-built screen — verify against the current state of lib/screens/my_festival_screen.dart and issue #414's status before treating any of it as already implemented.

When NOT to use this skill

  • Pure logic/provider/domain changes with no visible UI change (filter logic, sort logic, repository/service code, controller state) — see skill architecture-contract.
  • Test mechanics — golden update commands, semantics-testing strategy selection, mock generation, TDD workflow — see skill validation-and-qa. This skill tells you what a label/badge/layout should be; that skill tells you how to write the test that proves it.
  • My Festival / cloud-sync sequencing, phase gating, or campaign-level decisions — see skill my-festival-campaign. This skill only owns the visual-design constraints that campaign must respect (Part 6).
  • Route/URL contract questions, change classification, or "am I allowed to do this at all" — see skill change-control.

Provenance and maintenance

Written 2026-07-02. Verified against the working tree at that date: read in full — docs/code/accessibility.md, docs/code/widget-standards.md, docs/code/ui-components.md, docs/code/navigation.md, docs/planning/my-festival/vision.md, lib/router.dart, lib/app_theme.dart, lib/utils/navigation_helpers.dart, every file in lib/widgets/ named in the reuse table, lib/screens/my_festival_screen.dart, lib/screens/drinks_screen.dart, lib/screens/drink_detail_screen.dart. GitHub issues #414, #397, #40 fetched and read directly to confirm status, labels, and exact wording.

Re-verification commands for facts likely to drift:

# Golden file count/names — Part 1, rule 5
ls /home/user/cambridge-beer-festival-app/test/goldens/

# Festival-flash guard still present — Part 4.1
grep -n "currentFestival.id != festivalId" lib/screens/my_festival_screen.dart

# Route path for the My Festival / Favorites screen hasn't moved — Part 1, rule 3
grep -n "favorites" lib/router.dart

# Four-signal condition lines haven't shifted — Part 4.2 (line numbers are approximate, re-grep if stale)
grep -n "isLoading\|isRefreshing\|refreshNotice\|provider.error" lib/screens/drinks_screen.dart

# Search debounce constant — Part 4.5
grep -n "Duration(milliseconds" lib/screens/drinks_screen.dart

# Theme seed / per-festival theming status — Part 5 (check issue state, not just body)
gh issue view 414 --repo richardthe3rd/cambridge-beer-festival-app
gh issue view 40 --repo richardthe3rd/cambridge-beer-festival-app

# Shared widget set hasn't grown/shrunk — Part 2 reuse table
ls lib/widgets/

If docs/code/accessibility.md, docs/code/widget-standards.md, or docs/code/ui-components.md are edited, re-diff this skill's Parts 2–3 against them — they were the primary sources and this skill inlines their load-bearing content rather than just linking to it.