fix: preserve unsent desktop prompts across tab switches

Desktop non-session tabs unmount the active chat composer, so component-local draft refs disappeared before users returned to the session. Move the draft into per-session chat state and save it at session-switch and unmount boundaries, then clear it after submit.

Constraint: Settings and terminal tabs replace ActiveSession in ContentRouter.
Rejected: Persist drafts in localStorage | would add unnecessary persistence migration surface for a runtime-only draft.
Confidence: high
Scope-risk: narrow
Directive: Keep composer draft state scoped per session; do not move it back into component-only refs without covering unmount and remount.
Tested: bun run test src/components/chat/ChatInput.test.tsx --run
Tested: bun run check:desktop
Tested: bun run verify

desktop/src/components/chat/ChatInput.test.tsx

@@ -299,6 +299,23 @@ describe('ChatInput file mentions', () => {
     })
   })
 
+  it('restores an unsent composer draft after the composer unmounts', async () => {
+    const { unmount } = render(<ChatInput compact />)
+
+    const input = screen.getByRole('textbox') as HTMLTextAreaElement
+    fireEvent.change(input, {
+      target: { value: 'keep this prompt while I inspect another tab', selectionStart: 43 },
+    })
+    expect(input.value).toBe('keep this prompt while I inspect another tab')
+
+    unmount()
+    render(<ChatInput compact />)
+
+    await waitFor(() => {
+      expect(screen.getByRole('textbox')).toHaveValue('keep this prompt while I inspect another tab')
+    })
+  })
+
   it('shows branch and worktree launch controls for an empty active Git session', async () => {
     useSessionStore.setState({
       sessions: [{

desktop/src/components/chat/ChatInput.tsx

@@ -44,11 +44,6 @@ type GitInfo = SessionGitInfo
 
 type Attachment = ComposerAttachment
 
-type ComposerDraft = {
-  input: string
-  attachments: Attachment[]
-}
-
 type ChatInputProps = {
   variant?: 'default' | 'hero'
   compact?: boolean
@@ -96,7 +91,6 @@ export function ChatInput({ variant = 'default', compact = false }: ChatInputPro
   const slashMenuRef = useRef<HTMLDivElement>(null)
   const fileSearchRef = useRef<FileSearchMenuHandle>(null)
   const slashItemRefs = useRef<(HTMLButtonElement | null)[]>([])
-  const composerDraftsRef = useRef<Record<string, ComposerDraft>>({})
   const previousActiveTabIdRef = useRef<string | null>(null)
   const inputRef = useRef(input)
   const attachmentsRef = useRef(attachments)
@@ -136,6 +130,18 @@ export function ChatInput({ variant = 'default', compact = false }: ChatInputPro
   const addWorkspaceReference = useWorkspaceChatContextStore((s) => s.addReference)
   const removeWorkspaceReference = useWorkspaceChatContextStore((s) => s.removeReference)
   const clearWorkspaceReferences = useWorkspaceChatContextStore((s) => s.clearReferences)
+  const saveComposerDraft = useCallback((sessionId: string) => {
+    const draft = {
+      input: inputRef.current,
+      attachments: attachmentsRef.current,
+    }
+    const chatStore = useChatStore.getState()
+    if (draft.input.length === 0 && draft.attachments.length === 0) {
+      chatStore.clearComposerDraft(sessionId)
+      return
+    }
+    chatStore.setComposerDraft(sessionId, draft)
+  }, [])
 
   const isMemberSession = !!memberInfo
   const isActive = chatState !== 'idle'
@@ -178,13 +184,10 @@ export function ChatInput({ variant = 'default', compact = false }: ChatInputPro
     if (previousActiveTabId === activeTabId) return
 
     if (previousActiveTabId) {
-      composerDraftsRef.current[previousActiveTabId] = {
-        input: inputRef.current,
-        attachments: attachmentsRef.current,
-      }
+      saveComposerDraft(previousActiveTabId)
     }
 
-    const nextDraft = activeTabId ? composerDraftsRef.current[activeTabId] : undefined
+    const nextDraft = activeTabId ? useChatStore.getState().sessions[activeTabId]?.composerDraft : undefined
     setComposerInput(nextDraft?.input ?? '')
     setComposerAttachments(nextDraft?.attachments ?? [])
     setPlusMenuOpen(false)
@@ -195,7 +198,14 @@ export function ChatInput({ variant = 'default', compact = false }: ChatInputPro
     setAtFilter('')
     setAtCursorPos(-1)
     previousActiveTabIdRef.current = activeTabId
-  }, [activeTabId, setComposerAttachments, setComposerInput])
+  }, [activeTabId, saveComposerDraft, setComposerAttachments, setComposerInput])
+
+  useEffect(() => {
+    return () => {
+      const currentActiveTabId = previousActiveTabIdRef.current
+      if (currentActiveTabId) saveComposerDraft(currentActiveTabId)
+    }
+  }, [saveComposerDraft])
 
   useEffect(() => {
     textareaRef.current?.focus()
@@ -582,6 +592,8 @@ export function ChatInput({ variant = 'default', compact = false }: ChatInputPro
     })
     setComposerInput('')
     setComposerAttachments([])
+    useChatStore.getState().clearComposerDraft(activeTabId!)
+    if (targetSessionId !== activeTabId) useChatStore.getState().clearComposerDraft(targetSessionId)
     if (!isMemberSession) {
       clearWorkspaceReferences(activeTabId!)
       if (targetSessionId !== activeTabId) clearWorkspaceReferences(targetSessionId)

desktop/src/stores/chatStore.ts

@@ -10,6 +10,7 @@ import { randomSpinnerVerb } from '../config/spinnerVerbs'
 import { notifyDesktop } from '../lib/desktopNotifications'
 import { deriveSessionTitle, isPlaceholderSessionTitle } from '../lib/sessionTitle'
 import { AGENT_LIFECYCLE_TYPES } from '../types/team'
+import type { ComposerAttachment } from '../lib/composerAttachments'
 import type { MessageEntry } from '../types/session'
 import type { PermissionMode } from '../types/settings'
 import type { RuntimeSelection } from '../types/runtime'
@@ -32,6 +33,11 @@ import type {
 
 type ConnectionState = 'disconnected' | 'connecting' | 'connected' | 'reconnecting'
 
+export type ComposerDraftState = {
+  input: string
+  attachments: ComposerAttachment[]
+}
+
 export type PerSessionState = {
   messages: UIMessage[]
   chatState: ChatState
@@ -65,6 +71,7 @@ export type PerSessionState = {
     attachments?: UIAttachment[]
     nonce: number
   } | null
+  composerDraft?: ComposerDraftState | null
 }
 
 const DEFAULT_SESSION_STATE: PerSessionState = {
@@ -87,6 +94,7 @@ const DEFAULT_SESSION_STATE: PerSessionState = {
   activeGoal: null,
   elapsedTimer: null,
   composerPrefill: null,
+  composerDraft: null,
 }
 
 function createDefaultSessionState(): PerSessionState {
@@ -128,6 +136,8 @@ type ChatStore = {
     sessionId: string,
     prefill: { text: string; attachments?: UIAttachment[] },
   ) => void
+  setComposerDraft: (sessionId: string, draft: ComposerDraftState) => void
+  clearComposerDraft: (sessionId: string) => void
   clearMessages: (sessionId: string) => void
   handleServerMessage: (sessionId: string, msg: ServerMessage) => void
 }
@@ -403,6 +413,7 @@ export const useChatStore = create<ChatStore>((set, get) => ({
           connectionState: 'connecting',
           messages: existing?.messages ?? [],
           activeGoal: existing?.activeGoal ?? null,
+          composerDraft: existing?.composerDraft ?? null,
         },
       },
     }))
@@ -738,6 +749,29 @@ export const useChatStore = create<ChatStore>((set, get) => ({
     }))
   },
 
+  setComposerDraft: (sessionId, draft) => {
+    set((state) => {
+      const session = state.sessions[sessionId] ?? createDefaultSessionState()
+      return {
+        sessions: {
+          ...state.sessions,
+          [sessionId]: {
+            ...session,
+            composerDraft: draft,
+          },
+        },
+      }
+    })
+  },
+
+  clearComposerDraft: (sessionId) => {
+    set((state) => ({
+      sessions: updateSessionIn(state.sessions, sessionId, () => ({
+        composerDraft: null,
+      })),
+    }))
+  },
+
   clearMessages: (sessionId) => {
     clearPendingTaskToolUseIds(sessionId)
     set((s) => ({ sessions: updateSessionIn(s.sessions, sessionId, () => ({ messages: [], activeGoal: null, streamingText: '', chatState: 'idle' })) }))