feat(web): add continue hint in HappyComposer when switching to remote mode

When switching from local mode to remote mode, the placeholder text now
suggests users can type "continue" to resume interrupted tasks. This helps
users understand they can continue where they left off after experiencing
permission prompts that were stuck in the terminal during local mode.

web/src/components/AssistantChat/HappyComposer.tsx

@@ -94,8 +94,10 @@ export function HappyComposer(props: {
     const [showSettings, setShowSettings] = useState(false)
     const [isAborting, setIsAborting] = useState(false)
     const [isSwitching, setIsSwitching] = useState(false)
+    const [showContinueHint, setShowContinueHint] = useState(false)
 
     const textareaRef = useRef<HTMLTextAreaElement>(null)
+    const prevControlledByUser = useRef(controlledByUser)
 
     useEffect(() => {
         setInputState((prev) => {
@@ -104,6 +106,17 @@ export function HappyComposer(props: {
         })
     }, [composerText])
 
+    // Track one-time "continue" hint after switching from local to remote.
+    useEffect(() => {
+        if (prevControlledByUser.current === true && controlledByUser === false) {
+            setShowContinueHint(true)
+        }
+        if (controlledByUser) {
+            setShowContinueHint(false)
+        }
+        prevControlledByUser.current = controlledByUser
+    }, [controlledByUser])
+
     const { haptic: platformHaptic, isTouch } = usePlatform()
     const activeWord = useActiveWord(inputState.text, inputState.selection, autocompletePrefixes)
     const [suggestions, selectedIndex, moveUp, moveDown, clearSuggestions] = useActiveSuggestions(
@@ -283,6 +296,10 @@ export function HappyComposer(props: {
         setShowSettings(prev => !prev)
     }, [haptic])
 
+    const handleSubmit = useCallback(() => {
+        setShowContinueHint(false)
+    }, [])
+
     const handlePermissionChange = useCallback((mode: PermissionMode) => {
         if (!onPermissionModeChange || controlsDisabled) return
         onPermissionModeChange(mode)
@@ -438,7 +455,7 @@ export function HappyComposer(props: {
                             <ComposerPrimitive.Input
                                 ref={textareaRef}
                                 autoFocus={!controlsDisabled && !isTouch}
-                                placeholder="Type a message..."
+                                placeholder={showContinueHint ? "Type 'continue' to resume..." : "Type a message..."}
                                 disabled={controlsDisabled}
                                 maxRows={5}
                                 submitOnEnter
@@ -446,6 +463,7 @@ export function HappyComposer(props: {
                                 onChange={handleChange}
                                 onSelect={handleSelect}
                                 onKeyDown={handleKeyDown}
+                                onSubmit={handleSubmit}
                                 className="flex-1 resize-none bg-transparent text-sm leading-snug text-[var(--app-fg)] placeholder-[var(--app-hint)] focus:outline-none disabled:cursor-not-allowed disabled:opacity-50"
                             />
                         </div>