feat(desktop): read-only spectator transcript for subagent watch windows

Subagent session pop-outs (`watch=1`) spectate a run driven elsewhere, so
editing/steering the transcript from there makes no sense. Gate the composer
and the user-bubble mutations on `isWatchWindow()`:

- hide the composer (folds into `showChatBar`)
- user prompts become a read-only button that toggles the 2-line clamp so long
  prompts stay fully readable, instead of opening the edit composer
- drop the stop/restore actions and the checkpoint branch-picker

Keyed off the narrow `isWatchWindow()` (not `isSecondaryWindow()`), so the
new-session and cmd-click pop-outs are unaffected.

apps/desktop/src/app/chat/index.tsx

@@ -45,7 +45,7 @@ import {
   $sessions,
   sessionPinId
 } from '@/store/session'
-import { isSecondaryWindow } from '@/store/windows'
+import { isSecondaryWindow, isWatchWindow } from '@/store/windows'
 import type { ModelOptionsResponse } from '@/types/hermes'
 
 import { routeSessionId } from '../routes'
@@ -342,8 +342,9 @@ export function ChatView({
 
   const threadLoading = threadLoadingState(loadingSession, busy, awaitingResponse, lastVisibleIsUser)
   // Hide the composer in the exhausted error state too: there's no live runtime
-  // to send to until a retry rebinds one.
-  const showChatBar = !loadingSession && !resumeExhausted
+  // to send to until a retry rebinds one. Watch windows are pure spectators of a
+  // subagent run driven elsewhere — no composer, transcript is read-only.
+  const showChatBar = !loadingSession && !resumeExhausted && !isWatchWindow()
   const threadKey = selectedSessionId || activeSessionId || (isRoutedSessionView ? location.pathname : 'new')
 
   const modelOptionsQuery = useQuery<ModelOptionsResponse>({

apps/desktop/src/components/assistant-ui/thread.tsx

@@ -104,6 +104,7 @@ import { $activeSessionAwaitingInput } from '@/store/prompts'
 import { $connection } from '@/store/session'
 import { notifyThreadEditClose, notifyThreadEditOpen } from '@/store/thread-scroll'
 import { $voicePlayback } from '@/store/voice-playback'
+import { isWatchWindow } from '@/store/windows'
 
 type ThreadLoadingState = 'response' | 'session'
 interface RestoreMessageTarget {
@@ -1020,6 +1021,13 @@ const UserMessage: FC<{
   const lastClampHeightRef = useRef(-1)
   const lineHeightRef = useRef(0)
 
+  // Watch windows spectate a subagent run driven elsewhere — prompts can't be
+  // edited, restored, or stopped from here. The bubble stays a button that
+  // toggles the 2-line clamp so long prompts are still fully readable.
+  const readOnly = isWatchWindow()
+  const [expanded, setExpanded] = useState(false)
+  const clampActive = !(readOnly && expanded)
+
   const measureClamp = useCallback((entries: readonly ResizeObserverEntry[]) => {
     const inner = clampInnerRef.current
     const outer = inner?.parentElement
@@ -1070,11 +1078,11 @@ const UserMessage: FC<{
 
   const hasBody = messageText.trim().length > 0
   const isLatestUser = messageId === latestUserId
-  const showStop = isLatestUser && threadRunning && Boolean(onCancel)
+  const showStop = !readOnly && isLatestUser && threadRunning && Boolean(onCancel)
   // Restore (re-run this exact prompt) is available everywhere the Stop button
   // isn't — including mid-stream on older prompts, since the action interrupts
   // the live turn before rewinding.
-  const showRestore = !showStop && Boolean(onRequestRestoreConfirm) && hasBody
+  const showRestore = !readOnly && !showStop && Boolean(onRequestRestoreConfirm) && hasBody
 
   const bubbleClassName = cn(
     USER_BUBBLE_BASE_CLASS,
@@ -1086,7 +1094,10 @@ const UserMessage: FC<{
     // Render the user's text through a minimal markdown pipeline:
     // backtick `code` and ``` fenced ``` blocks, with directive chips
     // (`@file:` etc.) still resolved inside the plain-text spans.
-    <div className="sticky-human-clamp" data-clamped={bodyClamped ? 'true' : undefined}>
+    <div
+      className={cn(clampActive && 'sticky-human-clamp')}
+      data-clamped={clampActive && bodyClamped ? 'true' : undefined}
+    >
       {/* Match the edit composer's collapsed line box (min-h-[1.25rem]) so
           clicking to edit can't grow the bubble by a sub-pixel and reflow the
           turn 1px. */}
@@ -1114,20 +1125,41 @@ const UserMessage: FC<{
         <ActionBarPrimitive.Root className="relative w-full max-w-full" data-slot="aui_user-bubble-actions">
           <div className="human-message-with-todos-wrapper flex w-full flex-col gap-0">
             <div className="relative w-full">
-              {/* Always editable — clicking opens the edit composer even while a
-                  turn streams; sending the edit reverts (interrupt + rewind). */}
-              <ActionBarPrimitive.Edit asChild>
+              {readOnly ? (
+                // Spectator transcript: clicking only toggles the clamp so the
+                // full prompt is readable — never opens an edit composer.
                 <button
-                  aria-label={copy.editMessage}
-                  className={bubbleClassName}
-                  onClick={() => triggerHaptic('selection')}
-                  onPointerDown={() => notifyThreadEditOpen()}
-                  title={copy.editMessage}
+                  aria-expanded={bodyClamped ? expanded : undefined}
+                  className={cn(bubbleClassName, !bodyClamped && 'cursor-default')}
+                  onClick={() => {
+                    if (!bodyClamped) {
+                      return
+                    }
+
+                    triggerHaptic('selection')
+                    setExpanded(value => !value)
+                  }}
+                  title={bodyClamped ? (expanded ? t.common.collapse : copy.expandMessage) : undefined}
                   type="button"
                 >
                   {bubbleContent}
                 </button>
-              </ActionBarPrimitive.Edit>
+              ) : (
+                // Always editable — clicking opens the edit composer even while a
+                // turn streams; sending the edit reverts (interrupt + rewind).
+                <ActionBarPrimitive.Edit asChild>
+                  <button
+                    aria-label={copy.editMessage}
+                    className={bubbleClassName}
+                    onClick={() => triggerHaptic('selection')}
+                    onPointerDown={() => notifyThreadEditOpen()}
+                    title={copy.editMessage}
+                    type="button"
+                  >
+                    {bubbleContent}
+                  </button>
+                </ActionBarPrimitive.Edit>
+              )}
               {(showStop || showRestore) && (
                 <div className="pointer-events-none absolute right-2 bottom-2 z-10 flex items-center justify-center opacity-0 transition-opacity group-hover/user-message:opacity-100 group-focus-within/user-message:opacity-100">
                   {showStop ? (
@@ -1171,7 +1203,10 @@ const UserMessage: FC<{
               )}
             </div>
             <BranchPickerPrimitive.Root
-              className="checkpoint-container flex items-center gap-1 pb-0 pt-1 pl-1.5 text-[0.75rem] leading-none text-(--ui-text-tertiary)"
+              className={cn(
+                'checkpoint-container flex items-center gap-1 pb-0 pt-1 pl-1.5 text-[0.75rem] leading-none text-(--ui-text-tertiary)',
+                readOnly && 'hidden'
+              )}
               hideWhenSingleBranch
             >
               <span aria-hidden className="checkpoint-icon size-1.5 rounded-full border border-current" />

apps/desktop/src/i18n/en.ts

@@ -2010,6 +2010,7 @@ export const en: Translations = {
       stopReading: 'Stop reading',
       readAloud: 'Read aloud',
       editMessage: 'Edit message',
+      expandMessage: 'Expand message',
       scrollToBottom: 'Scroll to bottom',
       stop: 'Stop',
       restorePrevious: 'Restore previous checkpoint',

apps/desktop/src/i18n/types.ts

@@ -1657,6 +1657,7 @@ export interface Translations {
       stopReading: string
       readAloud: string
       editMessage: string
+      expandMessage: string
       scrollToBottom: string
       stop: string
       restorePrevious: string

apps/desktop/src/i18n/zh.ts

@@ -2177,6 +2177,7 @@ export const zh: Translations = {
       stopReading: '停止朗读',
       readAloud: '朗读',
       editMessage: '编辑消息',
+      expandMessage: '展开消息',
       scrollToBottom: '滚动到底部',
       stop: '停止',
       restorePrevious: '恢复上一个检查点',