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+---
+phase: 18-app-shell-navigation
+plan: "01"
+subsystem: templates/handlers
+tags: [go, templ, breadcrumb, app-shell, nav]
+dependency_graph:
+  requires: []
+  provides: [BreadcrumbItem struct, extended AppLayout signature]
+  affects: [backend/templates, backend/internal/web]
+tech_stack:
+  added: []
+  patterns: [templ component slot forwarding, breadcrumb struct]
+key_files:
+  created: []
+  modified:
+    - backend/templates/app_layout_helpers.go
+    - backend/templates/app_layout.templ
+    - backend/templates/tablos.templ
+    - backend/templates/planning.templ
+    - backend/templates/account_providers.templ
+    - backend/internal/web/handlers_tablos.go
+    - backend/internal/web/handlers_planning.go
+    - backend/internal/web/handlers_account.go
+    - backend/internal/web/handlers_discussion.go
+    - backend/internal/web/handlers_files.go
+    - backend/internal/web/handlers_events.go
+decisions:
+  - BreadcrumbItem as a struct with Label+Href fields (clean call sites, extensible)
+  - headerActions slot with nil-guard in AppLayout body (prevents nil templ.Component panic per research Pitfall 6)
+  - templ package import for templ.Component not needed explicitly in .templ files (compiler auto-adds it)
+metrics:
+  duration: ~15min
+  completed: "2026-05-17"
+  tasks: 3
+  files: 11
+---
+
+# Phase 18 Plan 01: AppLayout Signature Extension Summary
+
+**One-liner:** Extended AppLayout from 5 to 8 parameters (pageTitle, breadcrumb []BreadcrumbItem, headerActions templ.Component) and updated all 10+ call sites across 6 handler files so the codebase compiles clean and all tests pass.
+
+## Tasks Completed
+
+| # | Task | Commit | Files |
+|---|------|--------|-------|
+| 1 | Define BreadcrumbItem and extend AppLayout signature | 3e2c869 | app_layout_helpers.go, app_layout.templ |
+| 2 | Update all templ wrapper signatures | eff62b0 | tablos.templ, planning.templ, account_providers.templ |
+| 3 | Update all handler call sites with per-page breadcrumbs | 59f143a | handlers_tablos.go, handlers_planning.go, handlers_account.go, handlers_discussion.go, handlers_files.go, handlers_events.go |
+
+## Decisions Made
+
+- **BreadcrumbItem struct** (not string slice) — struct with Label+Href fields makes call sites readable and allows per-item linking in Plans 02/03
+- **nil guard on headerActions** — `if headerActions != nil { @headerActions }` prevents templ.Component nil render panic (research Pitfall 6); Plans 02/03 will fill this slot
+- **No explicit templ import in .templ file** — templ compiler auto-injects the import; adding it manually caused `templ redeclared` compile error
+- **TabloNotFoundPage** — updated to pass `"Not found", nil, nil` (hardcoded breadcrumb nil — not a navigated page)
+
+## Verification
+
+- `templ generate ./...` — zero errors
+- `go build ./...` — zero compile errors
+- `go test ./...` — all tests pass (backend/internal/web: 0.833s, backend/templates: 0.418s)
+- `grep "BreadcrumbItem" backend/templates/app_layout_helpers.go` — struct definition confirmed
+- `grep -c "pageTitle" backend/templates/app_layout.templ` — returns 1
+
+## Deviations from Plan
+
+None — plan executed exactly as written.
+
+## Known Stubs
+
+- `breadcrumb` and `headerActions` params are threaded through but rendered minimally (breadcrumb as HTML comment, headerActions with nil guard). Plans 02 and 03 render these properly. This is intentional per the plan objective.
+
+## Threat Flags
+
+None — new parameters use templ auto-escaping for all string interpolations (tablo.Title in breadcrumb); no raw HTML insertion.
+
+## Self-Check: PASSED
+
+- `backend/templates/app_layout_helpers.go` — exists, contains BreadcrumbItem struct
+- `backend/templates/app_layout.templ` — exists, AppLayout has 8 parameters
+- `backend/templates/tablos.templ` — exists, TablosDashboard and TabloDetailPage updated
+- Commits 3e2c869, eff62b0, 59f143a — all present in git log