feat(layout): Plan 2.5 P1 foundation — APP_NAVIGATION + walkNavTree + AppBreadcrumb

Per RFC-WS-PRIMEVUE-PLAN-2-5 §8 step 1. Foundation scaffolding only —
no shell fixes, no Public Sans removal, no useShellUiStore changes
(P2–P6 scope).

Implements:
- theme darkModeSelector verified at '.dark' (already correct in
  plugins/primevue/index.ts — config site is here, not theme.ts).
- src/config/navigation.ts: APP_NAVIGATION registry per AD-2.5-B1
  (Dashboard entry only — v2-dashboard is the only v2 route today).
- src/composables/useBreadcrumb.ts: walkNavTree pure helper +
  useNavBreadcrumb composable per AD-2.5-B1. The legacy meta-based
  useBreadcrumb is preserved (consumed by AppTopbar, P1 may not
  touch AppTopbar); P4 retires it and renames useNavBreadcrumb.
- src/components-v2/layout/AppBreadcrumb.vue: layout primitive
  wrapping PrimeVue Breadcrumb, consuming useNavBreadcrumb.
- Tests: walkNavTree (4 specs, co-located), AppBreadcrumb mount
  (2 specs, tests/component/layouts/).

Suite 564 → 570 (+6, all new specs green). vue-tsc clean. Scoped
ESLint clean.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

apps/app/src/components-v2/layout/AppBreadcrumb.vue

@@ -0,0 +1,53 @@
+<script setup lang="ts">
+/**
+ * AppBreadcrumb — layout primitive per RFC-WS-PRIMEVUE-PLAN-2-5 AD-2.5-B1.
+ *
+ * Consumes `useNavBreadcrumb` (registry-driven; data derives from
+ * APP_NAVIGATION + the current route name). Wired into AppTopbar in P5
+ * (RFC §5.2 Fix 2) — standalone in P1.
+ *
+ * Naming note: imports `useNavBreadcrumb` (not the literal `useBreadcrumb`
+ * the AD specifies) because the legacy meta-based `useBreadcrumb` is still
+ * consumed by AppTopbar; P1 may not touch AppTopbar (P4–P6 scope). P4
+ * retires the legacy API and renames `useNavBreadcrumb` → `useBreadcrumb`.
+ */
+
+import { computed } from 'vue'
+import Breadcrumb from 'primevue/breadcrumb'
+import { useNavBreadcrumb } from '@/composables/useBreadcrumb'
+
+const crumbs = useNavBreadcrumb()
+
+const items = computed(() =>
+  crumbs.value.map(c => ({
+    label: c.label,
+    route: c.routeName ? { name: c.routeName } : undefined,
+  })),
+)
+</script>
+
+<template>
+  <Breadcrumb
+    :model="items"
+    :pt="{
+      root: { class: 'border-none p-0 bg-transparent' },
+      list: { class: 'gap-1' },
+    }"
+  >
+    <template #item="{ item }">
+      <RouterLink
+        v-if="item.route"
+        :to="item.route"
+        class="text-sm text-surface-600 hover:text-surface-900 dark:text-surface-400 dark:hover:text-surface-100 transition-colors"
+      >
+        {{ item.label }}
+      </RouterLink>
+      <span
+        v-else
+        class="text-sm font-medium text-surface-900 dark:text-surface-100"
+      >
+        {{ item.label }}
+      </span>
+    </template>
+  </Breadcrumb>
+</template>

apps/app/src/composables/__tests__/useBreadcrumb.spec.ts

@@ -1,6 +1,7 @@
 import { describe, expect, it } from 'vitest'
-import { toBreadcrumbItems } from '@/composables/useBreadcrumb'
+import { toBreadcrumbItems, walkNavTree } from '@/composables/useBreadcrumb'
 import type { BreadcrumbRouteRecord } from '@/composables/useBreadcrumb'
+import type { NavItem } from '@/config/navigation'
 
 // ---------------------------------------------------------------------------
 // Fixtures
@@ -149,3 +150,53 @@ describe('toBreadcrumbItems', () => {
     expect(items[0].label).toBe('Dashboard')
   })
 })
+
+// ---------------------------------------------------------------------------
+// AD-2.5-B1 — walkNavTree (registry-driven breadcrumb)
+// Local FIXTURE keeps these specs independent of APP_NAVIGATION content.
+// ---------------------------------------------------------------------------
+
+const FIXTURE: NavItem[] = [
+  { key: 'a', label: 'A', routeName: 'a' },
+  {
+    key: 'b',
+    label: 'B',
+    children: [
+      { key: 'b.1', label: 'B-1', routeName: 'b-1' },
+      {
+        key: 'b.2',
+        label: 'B-2',
+        children: [
+          { key: 'b.2.1', label: 'B-2-1', routeName: 'b-2-1' },
+        ],
+      },
+    ],
+  },
+]
+
+describe('walkNavTree (AD-2.5-B1)', () => {
+  it('returns single-entry chain for a top-level leaf', () => {
+    expect(walkNavTree(FIXTURE, 'a')).toEqual([
+      { label: 'A', routeName: 'a' },
+    ])
+  })
+
+  it('returns full chain for a nested leaf', () => {
+    expect(walkNavTree(FIXTURE, 'b-1')).toEqual([
+      { label: 'B', routeName: undefined },
+      { label: 'B-1', routeName: 'b-1' },
+    ])
+  })
+
+  it('returns full chain for a deeply nested leaf', () => {
+    expect(walkNavTree(FIXTURE, 'b-2-1')).toEqual([
+      { label: 'B', routeName: undefined },
+      { label: 'B-2', routeName: undefined },
+      { label: 'B-2-1', routeName: 'b-2-1' },
+    ])
+  })
+
+  it('returns empty array for an unmatched route', () => {
+    expect(walkNavTree(FIXTURE, 'nonexistent')).toEqual([])
+  })
+})

apps/app/src/composables/useBreadcrumb.ts

@@ -2,9 +2,10 @@ import { computed } from 'vue'
 import { useRoute } from 'vue-router'
 import type { ComputedRef } from 'vue'
 import type { RouteLocationRaw } from 'vue-router'
+import { APP_NAVIGATION, type NavItem } from '@/config/navigation'
 
 // ---------------------------------------------------------------------------
-// Types
+// Types — legacy (meta-based, consumed by AppTopbar pre-P4)
 // ---------------------------------------------------------------------------
 
 /** A single breadcrumb item. `to` is absent for the current (last) item. */
@@ -81,8 +82,11 @@ export interface UseBreadcrumbReturn {
  * Composable that derives breadcrumb items from the current route's
  * `matched` array. Reactive — updates automatically on navigation.
  *
- * Composables zone may NOT import from @/navigation — do not add
- * route-level nav helpers here.
+ * NOTE (AD-2.5-B1): this `route.matched` + `meta` derivation is the
+ * pre-Plan-2.5 mechanism, still consumed by AppTopbar. P4 (RFC §8
+ * step 4) migrates AppTopbar to `useNavBreadcrumb` below; after that,
+ * this legacy function and its types should be retired and
+ * `useNavBreadcrumb` renamed to `useBreadcrumb` as the single SoT.
  */
 export function useBreadcrumb(): UseBreadcrumbReturn {
   const route = useRoute()
@@ -93,3 +97,66 @@ export function useBreadcrumb(): UseBreadcrumbReturn {
 
   return { items }
 }
+
+// ---------------------------------------------------------------------------
+// AD-2.5-B1 — registry-driven breadcrumb (Plan 2.5 P1 foundation)
+// ---------------------------------------------------------------------------
+
+/**
+ * Breadcrumb item derived from APP_NAVIGATION. Distinct from the legacy
+ * `BreadcrumbItem` above which carries a `RouteLocationRaw to` field;
+ * this shape carries a route NAME, mapped at render time to
+ * `{ name: routeName }`. Both shapes reconcile in P4 when AppTopbar
+ * migrates and the legacy API is removed.
+ */
+export interface NavBreadcrumbItem {
+  label: string
+  routeName?: string
+}
+
+/**
+ * Walks a NavItem tree to find the chain from root to the leaf whose
+ * `routeName` matches the given name. Returns an empty array if no match.
+ *
+ * AD-2.5-B1: pure function — unit-testable without router or component mount.
+ */
+export function walkNavTree(
+  tree: NavItem[],
+  routeName: string,
+  acc: NavBreadcrumbItem[] = [],
+): NavBreadcrumbItem[] {
+  for (const node of tree) {
+    const next = [...acc, { label: node.label, routeName: node.routeName }]
+
+    if (node.routeName === routeName)
+      return next
+
+    if (node.children) {
+      const childMatch = walkNavTree(node.children, routeName, next)
+
+      if (childMatch.length > 0)
+        return childMatch
+    }
+  }
+
+  return []
+}
+
+/**
+ * Returns the breadcrumb chain for the current route, derived from
+ * APP_NAVIGATION. Empty array when `route.name` is unset or no match.
+ *
+ * AD-2.5-B1. Transitional name: in P4 (RFC §8 step 4), AppTopbar
+ * migrates from the legacy `useBreadcrumb` above to this composable;
+ * after that, rename this to `useBreadcrumb` and drop the legacy API.
+ */
+export function useNavBreadcrumb(): ComputedRef<NavBreadcrumbItem[]> {
+  const route = useRoute()
+
+  return computed<NavBreadcrumbItem[]>(() => {
+    if (!route.name)
+      return []
+
+    return walkNavTree(APP_NAVIGATION, String(route.name))
+  })
+}

apps/app/src/config/navigation.ts

@@ -0,0 +1,44 @@
+// AD-2.5-B1: central navigation registry.
+// Single source of truth for sidebar rendering AND breadcrumb derivation.
+// Future extensions (role filtering, feature flags, dynamic ordering) are
+// explicit follow-up RFCs — DO NOT add those fields here without one.
+//
+// As of Plan 2.5 P1, only one v2 route exists (/v2/dashboard → v2-dashboard).
+// As pages-v2/ grows, add an entry per route here so both the sidebar (via
+// SidebarNav, wired in P4) and the breadcrumb (via useNavBreadcrumb) update
+// from one place.
+
+export interface NavItem {
+
+  /** Stable identifier, dot-namespaced (e.g., 'events.volunteers'). */
+  key: string
+
+  /** Display string shown in sidebar and breadcrumb. */
+  label: string
+
+  /** Vue-router route name; leaf nodes only. Branch nodes omit this. */
+  routeName?: string
+
+  /**
+   * Icon name in the project's `tabler-X` (dash-prefixed) convention,
+   * passed to `<Icon name="tabler-X" />`. Note: this deviates from the
+   * AD-2.5-B1 example which uses Iconify-standard `tabler:X` — the
+   * codebase's Icon.vue / iconify plugin pipeline expects dash-prefixed.
+   */
+  icon?: string
+
+  /** Submodule nesting. */
+  children?: NavItem[]
+
+  /** Exclude from sidebar but allow breadcrumb walk to traverse. */
+  hidden?: boolean
+}
+
+export const APP_NAVIGATION: NavItem[] = [
+  {
+    key: 'dashboard',
+    label: 'Dashboard',
+    routeName: 'v2-dashboard',
+    icon: 'tabler-home',
+  },
+]