diff --git a/apps/desktop/src/components/desktop-install-overlay.test.tsx b/apps/desktop/src/components/desktop-install-overlay.test.tsx
index ce3b9a04548f..1e4e384cb111 100644
--- a/apps/desktop/src/components/desktop-install-overlay.test.tsx
+++ b/apps/desktop/src/components/desktop-install-overlay.test.tsx
@@ -52,6 +52,33 @@ function installDesktopMock(state: DesktopBootstrapState) {
   return desktop
 }
 
+// Resolve the instant a node commits, via MutationObserver rather than
+// waitFor's polling timer. findBy* only settles on a timer tick, by which
+// point React has already drained its passive effects — that hides any bug
+// living in the window between paint and effect.
+function whenPresent(text: string): Promise<HTMLElement> {
+  return new Promise(resolve => {
+    const existing = screen.queryByText(text)
+
+    if (existing) {
+      resolve(existing)
+
+      return
+    }
+
+    const observer = new MutationObserver(() => {
+      const node = screen.queryByText(text)
+
+      if (node) {
+        observer.disconnect()
+        resolve(node)
+      }
+    })
+
+    observer.observe(document.body, { childList: true, subtree: true, characterData: true })
+  })
+}
+
 beforeEach(() => {
   vi.restoreAllMocks()
 })
@@ -120,6 +147,56 @@ describe('DesktopInstallOverlay first-run setup', () => {
     expect(install.disabled).toBe(false)
   })
 
+  it('keeps the local-start error when the first snapshot commits under the click', async () => {
+    const desktop = installDesktopMock(
+      bootstrapState({
+        setupChoice: { platform: 'win32', activeRoot: 'C:\\Users\\me\\AppData\\Local\\hermes\\hermes-agent' }
+      })
+    )
+
+    desktop.continueBootstrapLocal = undefined as never
+    render(<DesktopInstallOverlay />)
+
+    // Click the instant the choice paints, before React drains the passive
+    // effect that reacts to the first snapshot. A loaded runner hits this
+    // window by accident; observing the DOM directly hits it every time.
+    const install = (await whenPresent('Install Hermes locally')).closest('button') as HTMLButtonElement
+    fireEvent.click(install)
+
+    await act(async () => {
+      await Promise.resolve()
+    })
+
+    expect(screen.queryByText('Local installation could not start. Restart Hermes Desktop and try again.')).toBeTruthy()
+  })
+
+  it('clears a stale local-start error when a repair presents a different root', async () => {
+    const desktop = installDesktopMock(
+      bootstrapState({
+        setupChoice: { platform: 'win32', activeRoot: 'C:\\Users\\me\\AppData\\Local\\hermes\\hermes-agent' }
+      })
+    )
+
+    desktop.continueBootstrapLocal = undefined as never
+    render(<DesktopInstallOverlay />)
+
+    fireEvent.click((await screen.findByText('Install Hermes locally')).closest('button') as HTMLButtonElement)
+    expect(
+      await screen.findByText('Local installation could not start. Restart Hermes Desktop and try again.')
+    ).toBeTruthy()
+
+    act(() => {
+      desktop.emitBootstrapEvent({
+        type: 'setup-choice',
+        active: false,
+        platform: 'win32',
+        activeRoot: 'C:\\Users\\me\\AppData\\Local\\hermes\\hermes-agent-repaired'
+      })
+    })
+
+    expect(screen.queryByText('Local installation could not start. Restart Hermes Desktop and try again.')).toBeNull()
+  })
+
   it('opens the remote connection form from the first-run choice', async () => {
     installDesktopMock(
       bootstrapState({
diff --git a/apps/desktop/src/components/desktop-install-overlay.tsx b/apps/desktop/src/components/desktop-install-overlay.tsx
index 8a56f93c8c45..4941f6dd6bc4 100644
--- a/apps/desktop/src/components/desktop-install-overlay.tsx
+++ b/apps/desktop/src/components/desktop-install-overlay.tsx
@@ -277,8 +277,6 @@ export function DesktopInstallOverlay({ enabled = true }: DesktopInstallOverlayP
   const [copied, setCopied] = useState(false)
   const [cancelling, setCancelling] = useState(false)
   const [remoteOpen, setRemoteOpen] = useState(false)
-  const [localStarting, setLocalStarting] = useState(false)
-  const [localStartError, setLocalStartError] = useState<string | null>(null)
   const [now, setNow] = useState(() => Date.now())
   const logEndRef = useRef<HTMLDivElement | null>(null)
 
@@ -347,11 +345,21 @@ export function DesktopInstallOverlay({ enabled = true }: DesktopInstallOverlayP
 
   // The choice remains mounted while main hands off to local bootstrap. Once
   // a manifest/failure takes ownership (or a later repair presents a fresh
-  // choice), clear the transient button state so it cannot leak across phases.
-  useEffect(() => {
-    setLocalStarting(false)
-    setLocalStartError(null)
-  }, [state.setupChoice?.activeRoot])
+  // choice), this transient button state must not leak across phases — so it
+  // records the root it was produced under and is read back only under that
+  // same root. Deriving it beats clearing it in an effect: the choice paints
+  // as soon as the first snapshot commits, and a click landing before such an
+  // effect flushed would have its error wiped before it ever rendered.
+  const [localStart, setLocalStart] = useState<{
+    root: string | null
+    starting: boolean
+    error: string | null
+  }>({ root: null, starting: false, error: null })
+
+  const activeRoot = state.setupChoice?.activeRoot ?? null
+  const forActiveRoot = localStart.root === activeRoot
+  const localStarting = forActiveRoot && localStart.starting
+  const localStartError = forActiveRoot ? localStart.error : null
 
   // Mount logic: show whenever a bootstrap is in flight, completed-with-error,
   // or actively running with a manifest. Hide entirely after a successful
@@ -417,8 +425,7 @@ export function DesktopInstallOverlay({ enabled = true }: DesktopInstallOverlayP
               className="rounded-lg border border-(--ui-stroke-tertiary) bg-(--ui-bg-quinary) p-4 text-left transition hover:bg-(--chrome-action-hover) disabled:cursor-wait disabled:opacity-60"
               disabled={localStarting}
               onClick={async () => {
-                setLocalStarting(true)
-                setLocalStartError(null)
+                setLocalStart({ root: activeRoot, starting: true, error: null })
 
                 try {
                   const desktop = window.hermesDesktop
@@ -429,8 +436,7 @@ export function DesktopInstallOverlay({ enabled = true }: DesktopInstallOverlayP
 
                   await desktop.continueBootstrapLocal()
                 } catch (err) {
-                  setLocalStartError(errorMessage(err))
-                  setLocalStarting(false)
+                  setLocalStart({ root: activeRoot, starting: false, error: errorMessage(err) })
                 }
               }}
               type="button"