Fix connect spinner stuck after a failed SSH connect

The run-picker Connect spinner never stopped when a connect failed. Root cause:
the `mountedRef` guard around the clearing setState. The ref's effect only set
it false on cleanup and never back to true on mount, so StrictMode's dev
mount→unmount→remount left it stuck false — the connect `finally` then skipped
clearing connectingHostIds and the row spun forever even after the error toast.

Remove the unnecessary mounted-guard entirely (a stale setState is a harmless
no-op in React 18) so the in-flight id is always cleared when the connect
settles. Add a regression test for the failed-connect path.

src/renderer/src/components/NewWorkspaceComposerCard.test.tsx

@@ -676,6 +676,26 @@ describe('NewWorkspaceComposerCard folder task source mode', () => {
     expect(apiMocks.sshConnect).toHaveBeenCalledWith({ targetId: 'bastion' })
   })
 
+  it('stops the connecting indicator when the connect fails', async () => {
+    // A failed connect must clear the spinner and restore the Connect button so the user
+    // can retry — the row can't stay stuck on "Connecting" after the error.
+    apiMocks.sshConnect.mockRejectedValue(new Error('connection refused'))
+    current = renderCard({
+      projectHostSetupOptions: [localReadyHostOption, disconnectedDevboxNeedsSetupHostOption],
+      selectedProjectHostSetupId: 'setup-local'
+    })
+
+    openRunTargetPicker(current.container)
+    await act(async () => {
+      findConnectButton('Devbox')?.click()
+    })
+
+    const devboxButton = findConnectButton('Devbox')
+    expect(devboxButton?.disabled).toBe(false)
+    expect(devboxButton?.textContent).toContain('Connect')
+    expect(devboxButton?.textContent).not.toContain('Connecting')
+  })
+
   it('opens the SSH host add dialog over the composer without leaving for Settings', () => {
     current = renderCard({
       projectHostSetupOptions: [localReadyHostOption, devboxNeedsSetupHostOption],

src/renderer/src/components/NewWorkspaceComposerCard.tsx

@@ -293,7 +293,6 @@ function WorkspaceRunTargetCombobox({
   const [connectingHostIds, setConnectingHostIds] = React.useState<ReadonlySet<string>>(
     () => new Set()
   )
-  const mountedRef = React.useRef(true)
   const readyHostOptions = React.useMemo(
     () =>
       hostOptions.filter(
@@ -321,12 +320,6 @@ function WorkspaceRunTargetCombobox({
     'Per-Workspace Environment'
   )
 
-  React.useEffect(() => {
-    return () => {
-      mountedRef.current = false
-    }
-  }, [])
-
   const handleHostSelect = React.useCallback(
     (setupId: string): void => {
       if (!readyHostOptions.some((candidate) => candidate.id === setupId)) {
@@ -360,16 +353,18 @@ function WorkspaceRunTargetCombobox({
       try {
         await onConnectHost(option)
       } finally {
-        if (mountedRef.current) {
-          setConnectingHostIds((current) => {
-            if (!current.has(option.hostId)) {
-              return current
-            }
-            const next = new Set(current)
-            next.delete(option.hostId)
-            return next
-          })
-        }
+        // Why: always clear the in-flight id when the connect settles (success, failure, or
+        // timeout) so the row's spinner stops. No mounted-guard — a stale setState on an
+        // unmounted component is a harmless no-op in React 18, and the guard's ref was the
+        // source of a StrictMode bug that left the spinner stuck.
+        setConnectingHostIds((current) => {
+          if (!current.has(option.hostId)) {
+            return current
+          }
+          const next = new Set(current)
+          next.delete(option.hostId)
+          return next
+        })
       }
     },
     [connectingHostIds, onConnectHost]