diff --git a/frontend/src/App.tsx b/frontend/src/App.tsx
index fba646d..7a48958 100644
--- a/frontend/src/App.tsx
+++ b/frontend/src/App.tsx
@@ -66,6 +66,14 @@ export default function App() {
   const [autosave, setAutosave] = useState<AutosaveSettings>(readAutosaveSettings)
   useEffect(() => subscribeAutosaveSettings(setAutosave), [])
 
+  // Provenance: which design the in-memory canvas was loaded as. Differs from
+  // activeDesignId (the selection) during a switch, so autosave gates on this to
+  // avoid writing one design's canvas under another's id. Ref mirror for the
+  // fire-time guard, which must read the live value without re-arming the timer.
+  const [loadedDesignId, setLoadedDesignId] = useState<string | null>(null)
+  const loadedDesignIdRef = useRef<string | null>(loadedDesignId)
+  useEffect(() => { loadedDesignIdRef.current = loadedDesignId }, [loadedDesignId])
+
   const [themeModalOpen, setThemeModalOpen] = useState(false)
   const [styleEditorType, setStyleEditorType] = useState<NodeType | null>(null)
   const [searchOpen, setSearchOpen] = useState(false)
@@ -133,9 +141,9 @@ export default function App() {
     enabled: autosave.enabled,
     delaySeconds: autosave.delay,
     hasUnsavedChanges,
-    activeDesignId,
+    designId: loadedDesignId,
     changeSignals: [nodes, edges],
-    getActiveDesignId: () => useDesignStore.getState().activeDesignId,
+    getLiveDesignId: () => loadedDesignIdRef.current,
     onSave: (designId) => { void handleSaveRef.current(designId, { silent: true }) },
   })
 
@@ -168,6 +176,9 @@ export default function App() {
     } catch {
       setFloorMap(null)
       loadCanvas(demoNodes, demoEdges)
+    } finally {
+      // Record provenance so autosave writes back under the design just loaded.
+      setLoadedDesignId(designId ?? null)
     }
   }, [loadCanvas, setTheme, setCustomStyle, setFloorMap])
 
@@ -186,6 +197,8 @@ export default function App() {
       setFloorMap(null)
       loadCanvas(demoNodes, demoEdges)
     }
+    // Record provenance so autosave writes back under the design just loaded.
+    setLoadedDesignId(designId)
   }, [loadCanvas, setTheme, setCustomStyle, setFloorMap])
 
   const loadDesignsAndCanvas = useCallback(async () => {
diff --git a/frontend/src/hooks/__tests__/useAutosave.test.ts b/frontend/src/hooks/__tests__/useAutosave.test.ts
index a299013..e114d14 100644
--- a/frontend/src/hooks/__tests__/useAutosave.test.ts
+++ b/frontend/src/hooks/__tests__/useAutosave.test.ts
@@ -6,21 +6,21 @@ interface Args {
   enabled?: boolean
   delaySeconds?: number
   hasUnsavedChanges?: boolean
-  activeDesignId?: string | null
+  designId?: string | null
   changeSignals?: unknown[]
-  getActiveDesignId?: () => string | null
+  getLiveDesignId?: () => string | null
   onSave?: (designId: string) => void
 }
 
 function args(over: Args = {}) {
-  const activeDesignId = 'activeDesignId' in over ? (over.activeDesignId ?? null) : 'design-a'
+  const designId = 'designId' in over ? (over.designId ?? null) : 'design-a'
   return {
     enabled: over.enabled ?? true,
     delaySeconds: over.delaySeconds ?? 5,
     hasUnsavedChanges: over.hasUnsavedChanges ?? true,
-    activeDesignId,
+    designId,
     changeSignals: over.changeSignals ?? [[], []],
-    getActiveDesignId: over.getActiveDesignId ?? (() => activeDesignId),
+    getLiveDesignId: over.getLiveDesignId ?? (() => designId),
     onSave: over.onSave ?? vi.fn(),
   }
 }
@@ -36,7 +36,8 @@ describe('useAutosave', () => {
     vi.advanceTimersByTime(4999)
     expect(onSave).not.toHaveBeenCalled()
     vi.advanceTimersByTime(1)
-    expect(onSave).toHaveBeenCalledExactlyOnceWith('design-a')
+    expect(onSave).toHaveBeenCalledTimes(1)
+    expect(onSave).toHaveBeenCalledWith('design-a')
   })
 
   it('does nothing when disabled', () => {
@@ -53,9 +54,9 @@ describe('useAutosave', () => {
     expect(onSave).not.toHaveBeenCalled()
   })
 
-  it('does nothing when there is no active design', () => {
+  it('does nothing when the canvas has no known provenance', () => {
     const onSave = vi.fn()
-    renderHook(() => useAutosave(args({ onSave, activeDesignId: null })))
+    renderHook(() => useAutosave(args({ onSave, designId: null })))
     vi.advanceTimersByTime(60_000)
     expect(onSave).not.toHaveBeenCalled()
   })
@@ -70,25 +71,27 @@ describe('useAutosave', () => {
     vi.advanceTimersByTime(4000)
     expect(onSave).not.toHaveBeenCalled()
     vi.advanceTimersByTime(1000)
-    expect(onSave).toHaveBeenCalledExactlyOnceWith('design-a')
+    expect(onSave).toHaveBeenCalledTimes(1)
   })
 
-  it('skips the save if the active design changed while the timer was pending', () => {
+  it('skips the save if a different canvas loaded while the timer was pending', () => {
     const onSave = vi.fn()
-    // Pinned at arm time = 'design-a', but live id has moved on to 'design-b'.
+    // Pinned provenance at arm time = 'design-a', but a switch loaded 'design-b'
+    // before the timer fired — the on-screen canvas is no longer design-a's.
     renderHook(() =>
-      useAutosave(args({ onSave, activeDesignId: 'design-a', getActiveDesignId: () => 'design-b' })),
+      useAutosave(args({ onSave, designId: 'design-a', getLiveDesignId: () => 'design-b' })),
     )
     vi.advanceTimersByTime(5000)
     expect(onSave).not.toHaveBeenCalled()
   })
 
-  it('saves under the pinned design id, not the live one, when they still match', () => {
+  it('saves under the pinned provenance id when it still matches at fire time', () => {
     const onSave = vi.fn()
     renderHook(() =>
-      useAutosave(args({ onSave, activeDesignId: 'design-a', getActiveDesignId: () => 'design-a' })),
+      useAutosave(args({ onSave, designId: 'design-a', getLiveDesignId: () => 'design-a' })),
     )
     vi.advanceTimersByTime(5000)
-    expect(onSave).toHaveBeenCalledExactlyOnceWith('design-a')
+    expect(onSave).toHaveBeenCalledTimes(1)
+    expect(onSave).toHaveBeenCalledWith('design-a')
   })
 })
diff --git a/frontend/src/hooks/useAutosave.ts b/frontend/src/hooks/useAutosave.ts
index e4ac35c..90b43c2 100644
--- a/frontend/src/hooks/useAutosave.ts
+++ b/frontend/src/hooks/useAutosave.ts
@@ -7,22 +7,28 @@ interface UseAutosaveOptions {
   delaySeconds: number
   /** True when the canvas has edits not yet persisted. */
   hasUnsavedChanges: boolean
-  /** The design the in-memory canvas currently belongs to. */
-  activeDesignId: string | null
+  /**
+   * The design the in-memory canvas actually belongs to — its *provenance*, set
+   * when a canvas is loaded, NOT the currently-selected design. These differ
+   * during a design switch: the selection flips synchronously while the new
+   * canvas loads asynchronously, so for a brief window the on-screen nodes still
+   * belong to the previous design. Gating on provenance (not selection) is what
+   * prevents saving one design's canvas under another design's id.
+   */
+  designId: string | null
   /**
    * Values that represent canvas edits (e.g. nodes, edges). Any change to one
    * of these resets the debounce timer, so the save only fires after a quiet
-   * period. Kept separate from the trigger flags so the caller controls exactly
-   * what counts as "activity".
+   * period. Its length MUST stay constant across renders (React requires a
+   * stable dependency-array size) — pass a fixed-shape array like [nodes, edges].
    */
-  changeSignals: unknown[]
+  changeSignals: readonly unknown[]
   /**
-   * Reads the *live* active design id at fire time. Used to detect that the user
-   * switched designs while the timer was pending — if so, the in-memory canvas
-   * now belongs to a different design and saving it under the pinned id would
-   * clobber the wrong design, so the save is skipped.
+   * Reads the *live* canvas provenance at fire time. If it no longer matches the
+   * id pinned when the timer was armed, a different canvas has since loaded, so
+   * the save is skipped rather than written under the wrong (now-stale) id.
    */
-  getActiveDesignId: () => string | null
+  getLiveDesignId: () => string | null
   /** Persist the canvas under the given design id. */
   onSave: (designId: string) => void
 }
@@ -36,30 +42,31 @@ export function useAutosave({
   enabled,
   delaySeconds,
   hasUnsavedChanges,
-  activeDesignId,
+  designId,
   changeSignals,
-  getActiveDesignId,
+  getLiveDesignId,
   onSave,
 }: UseAutosaveOptions): void {
   // Keep the latest callbacks in refs so the timer always calls the current
   // versions without re-arming (which would reset the debounce) on every render.
   const onSaveRef = useRef(onSave)
-  const getActiveDesignIdRef = useRef(getActiveDesignId)
+  const getLiveDesignIdRef = useRef(getLiveDesignId)
   useEffect(() => {
     onSaveRef.current = onSave
-    getActiveDesignIdRef.current = getActiveDesignId
+    getLiveDesignIdRef.current = getLiveDesignId
   })
 
   useEffect(() => {
-    if (!enabled || !hasUnsavedChanges || !activeDesignId) return
-    const designId = activeDesignId
+    if (!enabled || !hasUnsavedChanges || !designId) return
+    const pinnedDesignId = designId
     const t = setTimeout(() => {
-      // Skip if the active design changed while the timer was pending.
-      if (getActiveDesignIdRef.current() !== designId) return
-      onSaveRef.current(designId)
+      // Skip if a different canvas has loaded while the timer was pending.
+      if (getLiveDesignIdRef.current() !== pinnedDesignId) return
+      onSaveRef.current(pinnedDesignId)
     }, delaySeconds * 1000)
     return () => clearTimeout(t)
-    // changeSignals is spread so any canvas edit resets the debounce.
+    // changeSignals is spread so any canvas edit resets the debounce; its length
+    // must stay constant (documented on the option).
     // eslint-disable-next-line react-hooks/exhaustive-deps
-  }, [enabled, delaySeconds, hasUnsavedChanges, activeDesignId, ...changeSignals])
+  }, [enabled, delaySeconds, hasUnsavedChanges, designId, ...changeSignals])
 }
diff --git a/frontend/src/utils/__tests__/autosaveSettings.test.ts b/frontend/src/utils/__tests__/autosaveSettings.test.ts
index 3074c92..be31087 100644
--- a/frontend/src/utils/__tests__/autosaveSettings.test.ts
+++ b/frontend/src/utils/__tests__/autosaveSettings.test.ts
@@ -46,6 +46,11 @@ describe('autosaveSettings', () => {
     expect(readAutosaveSettings().delay).toBe(DEFAULT_AUTOSAVE_SETTINGS.delay)
   })
 
+  it('rejects a non-boolean enabled and falls back to default', () => {
+    localStorage.setItem('homelable.autosave', JSON.stringify({ enabled: 'yes', delay: 10 }))
+    expect(readAutosaveSettings().enabled).toBe(DEFAULT_AUTOSAVE_SETTINGS.enabled)
+  })
+
   it('notifies subscribers on write and stops after unsubscribe', () => {
     const listener = vi.fn()
     const unsubscribe = subscribeAutosaveSettings(listener)
diff --git a/frontend/src/utils/autosaveSettings.ts b/frontend/src/utils/autosaveSettings.ts
index 3b54941..266e0b0 100644
--- a/frontend/src/utils/autosaveSettings.ts
+++ b/frontend/src/utils/autosaveSettings.ts
@@ -19,7 +19,7 @@ export function readAutosaveSettings(): AutosaveSettings {
     if (!raw) return DEFAULT_AUTOSAVE_SETTINGS
     const parsed = JSON.parse(raw) as Partial<AutosaveSettings>
     return {
-      enabled: parsed.enabled ?? DEFAULT_AUTOSAVE_SETTINGS.enabled,
+      enabled: typeof parsed.enabled === 'boolean' ? parsed.enabled : DEFAULT_AUTOSAVE_SETTINGS.enabled,
       delay: typeof parsed.delay === 'number' && parsed.delay > 0 ? parsed.delay : DEFAULT_AUTOSAVE_SETTINGS.delay,
     }
   } catch {