diff --git a/.planning/STATE.md b/.planning/STATE.md
index c3cc6b3..a2d4bdf 100644
--- a/.planning/STATE.md
+++ b/.planning/STATE.md
@@ -233,6 +233,10 @@ Recent decisions affecting current work:
 - 20-02: Subscription-driven invalidation (not local state) — simplest approach, reuses existing React Query cache
 - 20-02: Silent onError callbacks — pages degrade to manual refresh when backend is not running
 - 20-02: No new packages needed — splitLink and httpSubscriptionLink ship with @trpc/client v11
+- 21-01: ErrorBoundary wraps Outlet only (not entire AppLayout) so nav shell survives render errors
+- 21-01: Toaster outside AppLayout as sibling — available even if layout breaks
+- 21-01: notFoundComponent uses shadcn Button with asChild + Link (consistent with component library)
+- 21-01: One success and one error toast per mutation — no toasts for query failures (those have inline error states)
 - 21-02: Skeleton component in components/ (not ui/) — app-specific, not a shadcn primitive
 - 21-02: Inbox skeleton lives in inbox.tsx route (not InboxList component) since InboxList receives pre-loaded data
 - 21-03: Removed disabled nav stubs (Agents, Tasks, Settings) — stubs create false promises for v2.0
diff --git a/.planning/phases/21-polish-integration/21-01-SUMMARY.md b/.planning/phases/21-polish-integration/21-01-SUMMARY.md
new file mode 100644
index 0000000..d9a6657
--- /dev/null
+++ b/.planning/phases/21-polish-integration/21-01-SUMMARY.md
@@ -0,0 +1,44 @@
+# Plan 21-01 Summary: Error Boundary & Toast Notifications
+
+## Result: COMPLETE
+
+**Duration:** ~3 min
+**Commits:** 2
+
+## What was done
+
+1. **Created ErrorBoundary component** (`packages/web/src/components/ErrorBoundary.tsx`)
+   - React class component with `getDerivedStateFromError` and `componentDidCatch`
+   - Renders centered error card: red AlertCircle icon, "Something went wrong" heading, error message in muted text, Reload button
+   - Styled with existing Tailwind classes matching the app's error state patterns
+
+2. **Created Sonner toast wrapper** (`packages/web/src/components/ui/sonner.tsx`)
+   - Thin wrapper exporting `Toaster` component from sonner
+   - Configured with `position="bottom-right"` and `richColors`
+
+3. **Wired into root route** (`packages/web/src/routes/__root.tsx`)
+   - `<ErrorBoundary>` wraps `<Outlet />` inside AppLayout so route-level render errors are caught without destroying the nav shell
+   - `<Toaster />` rendered as sibling to AppLayout for app-wide toast availability
+   - `notFoundComponent` updated with "Back to Dashboard" Button/Link pointing to /initiatives
+
+4. **Wired toast notifications into all mutation flows**
+   - `SpawnArchitectDropdown.tsx`: `toast.success("Architect spawned")` on success, `toast.error("Failed to spawn architect")` on error
+   - `ActionMenu.tsx`: `toast.success("Initiative archived")` on success, `toast.error("Failed to archive initiative")` on error
+   - `CreateInitiativeDialog.tsx`: `toast.success("Initiative created")` on success (inline error kept for form validation)
+   - `inbox.tsx`: `toast.success`/`toast.error` for both `resumeAgent` and `respondToMessage` mutations
+
+## Decisions
+
+- 21-01: ErrorBoundary wraps Outlet only (not entire AppLayout) so nav shell survives render errors
+- 21-01: Toaster outside AppLayout as sibling — available even if layout breaks
+- 21-01: notFoundComponent uses shadcn Button with asChild + Link (consistent with component library)
+- 21-01: CreateInitiativeDialog keeps inline form error in addition to toast (inline error shows specific validation message)
+- 21-01: One success and one error toast per mutation — no toasts for query failures (those have inline error states)
+
+## Verification
+
+- [x] `npx tsc --noEmit -p packages/web/tsconfig.app.json` — passes
+- [x] `npm run --workspace=packages/web build` — succeeds
+- [x] ErrorBoundary component exists and is wired into root route
+- [x] Toaster component rendered in root route
+- [x] All mutation callbacks use toast instead of (or in addition to) console.error