fix(desktop): hide side chat entries until a session has a conversation

A side chat forks the parent transcript, so the server rejects it for a
blank session. The new-session page still showed the side chat button in
its top-right corner, and every click only produced a "Start a
conversation before opening a side chat" toast.

Gate every way in on the session having a conversation: the top-right
button now only renders on mobile once the session has messages, and the
workspace launcher, its + menu and the /btw slash menu entry leave side
chat out of a blank session.

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

@@ -826,6 +826,21 @@ describe('ChatInput file mentions', () => {
     expect(getComposerText()).toBe('')
   })
 
+  it('leaves /btw out of the slash menu until the session has a conversation to fork', async () => {
+    useSessionStore.setState(state => ({ sessions: state.sessions.map(session => ({ ...session, messageCount: 0 })) }))
+    useChatStore.setState(state => ({ sessions: { [sessionId]: { ...state.sessions[sessionId]!, messages: [] } } }))
+    render(<ChatInput />)
+    const btwOptions = () => screen.queryAllByRole('option').filter(option => option.textContent?.startsWith('/btw'))
+    setComposerText('/bt', 3)
+    await act(async () => { await new Promise(resolve => setTimeout(resolve, 50)) })
+    expect(btwOptions()).toEqual([])
+
+    act(() => useChatStore.setState(state => ({ sessions: { [sessionId]: { ...state.sessions[sessionId]!, messages: [{ id: 'first', type: 'user_text', content: 'hi', timestamp: 1 }] } } })))
+    setComposerText('', 0)
+    setComposerText('/bt', 3)
+    await waitFor(() => expect(btwOptions()).toHaveLength(1))
+  })
+
   it('opens an empty full side chat with /btw without sending a main message', async () => {
     render(<ChatInput compact />)
     setComposerText('/btw', 4)

desktop/src/components/chat/ChatInput.tsx

@@ -336,6 +336,7 @@ export function ChatInput({ variant = 'default', compact = false, sessionId, vis
   const isHeroComposer = variant === 'hero' && !isMemberSession && !compact
   const resolvedWorkDir = activeSession?.workDir || gitInfo?.workDir || undefined
   const showLaunchControls = !isMemberSession && !sideChat && messageCount === 0
+  const sideChatAvailable = Boolean(sideChat) || messageCount > 0
   // `useCompactControls` is about room, so it asks the column how wide it is —
   // never "is a side panel open". Until a measurement lands (jsdom, first
   // paint) it defers to the caller's `compact`, which keeps the
@@ -665,8 +666,9 @@ export function ChatInput({ variant = 'default', compact = false, sessionId, vis
       names.add(name.toLowerCase())
       commands.push({ name, description: reference.description, kind: reference.kind })
     }
-    return commands.filter(isComposerSlashCommandVisible)
-  }, [agentSlashCommands, slashCommands, composerReferences, t])
+    // `/btw` forks the conversation so far; a blank session has none to fork.
+    return commands.filter(command => isComposerSlashCommandVisible(command) && (sideChatAvailable || command.name !== 'btw'))
+  }, [agentSlashCommands, slashCommands, composerReferences, sideChatAvailable, t])
 
   const filteredCommandGroups = useMemo(() => {
     return groupSlashCommands(filterSlashCommands(allSlashCommands, slashFilter))

desktop/src/components/workbench/WorkspaceAddMenu.tsx

@@ -13,13 +13,14 @@ export type WorkspaceAddMenuProps = {
   dock: WorkspaceDock
   initialFocus?: 'first' | 'last'
   reviewUnavailableReason?: string | null
+  sideChatAvailable?: boolean
   onSelect: (kind: WorkspaceTabKind) => void
   onClose: () => void
 }
 
 /** The empty dock owns a launcher; the + button owns a menu over its current content. */
 export function WorkspaceAddMenu({
-  id, anchorRef, dock, initialFocus, reviewUnavailableReason, onSelect, onClose,
+  id, anchorRef, dock, initialFocus, reviewUnavailableReason, sideChatAvailable, onSelect, onClose,
 }: WorkspaceAddMenuProps) {
   const t = useTranslation()
   const menuRef = useRef<HTMLDivElement>(null)
@@ -57,7 +58,7 @@ export function WorkspaceAddMenu({
       style={position.style}
       className="z-[var(--z-dropdown)] w-[260px] max-w-[calc(100vw-12px)] overflow-y-auto rounded-[var(--radius-lg)] border border-[var(--color-border)] bg-[var(--color-surface-container-lowest)] p-1 shadow-[var(--shadow-dropdown)]"
     >
-      <WorkspaceLauncher variant="menu" dock={dock} onSelect={onSelect} reviewUnavailableReason={reviewUnavailableReason} />
+      <WorkspaceLauncher variant="menu" dock={dock} onSelect={onSelect} reviewUnavailableReason={reviewUnavailableReason} sideChatAvailable={sideChatAvailable} />
     </div>,
     document.body,
   )

desktop/src/components/workbench/WorkspaceLauncher.test.tsx

@@ -22,6 +22,16 @@ describe('WorkspaceLauncher', () => {
     ])
   })
 
+  it('leaves side chat out while there is no conversation to fork', () => {
+    render(<WorkspaceLauncher onSelect={vi.fn()} sideChatAvailable={false} />)
+    expect(screen.getAllByRole('button').map((item) => item.getAttribute('data-testid'))).toEqual([
+      'workspace-launcher-review',
+      'workspace-launcher-terminal',
+      'workspace-launcher-browser',
+      'workspace-launcher-file',
+    ])
+  })
+
   it('advertises the four global resource shortcuts while clicks retain their dock', () => {
     render(<WorkspaceLauncher onSelect={vi.fn()} />)
     // The hint is what makes the launcher teach its own shortcuts rather than

desktop/src/components/workbench/WorkspaceLauncher.tsx

@@ -42,11 +42,19 @@ export type WorkspaceLauncherProps = {
    * missing feature.
    */
   reviewUnavailableReason?: string | null
+  /**
+   * A side chat forks the parent transcript, so a session with no
+   * conversation yet has nothing to fork. Unlike review, the entry is left
+   * out rather than disabled: it becomes available by talking, not by
+   * changing the folder.
+   */
+  sideChatAvailable?: boolean
 }
 
 export function WorkspaceLauncher({
   onSelect,
   reviewUnavailableReason,
+  sideChatAvailable = true,
   dock = 'side',
   variant = 'empty',
 }: WorkspaceLauncherProps) {
@@ -61,7 +69,7 @@ export function WorkspaceLauncher({
       className={menu ? '' : `flex min-h-0 flex-1 items-start justify-center overflow-y-auto ${compact ? 'px-4 py-2' : 'px-6 py-10'}`}
     >
       <ul className={menu ? 'space-y-px' : 'my-auto w-full max-w-[420px] space-y-px'} role={menu ? 'presentation' : undefined} aria-label={menu ? undefined : t('workspace.launcher.label')}>
-        {ENTRIES.filter(entry => dock !== 'bottom' || entry.kind !== 'side-chat').map(({ kind, labelKey, shortcut, Icon }) => {
+        {ENTRIES.filter(entry => entry.kind !== 'side-chat' || (dock !== 'bottom' && sideChatAvailable)).map(({ kind, labelKey, shortcut, Icon }) => {
           const disabledReason = kind === 'review' ? reviewUnavailableReason ?? null : null
           // The hint advertises the app command; a pointer choice uses this dock.
           const hint = shortcut ? formatWorkspaceShortcut(shortcut, platform) : null

desktop/src/components/workbench/WorkspaceSurface.tsx

@@ -31,6 +31,8 @@ export type WorkspaceSurfaceProps = {
   cwd: string
   /** Reason the review entry is unavailable here, e.g. "not a Git repository". */
   reviewUnavailableReason?: string | null
+  /** False until the session has a conversation for a side chat to fork. */
+  sideChatAvailable?: boolean
   /**
    * Whether this dock is on screen. The bottom dock stays mounted while hidden
    * so xterm keeps its geometry, so "mounted" and "visible" are not the same
@@ -51,6 +53,7 @@ export function WorkspaceSurface({
   dock,
   cwd,
   reviewUnavailableReason = null,
+  sideChatAvailable = true,
   visible = true,
 }: WorkspaceSurfaceProps) {
   const t = useTranslation()
@@ -237,6 +240,7 @@ export function WorkspaceSurface({
             onSelect={handleLauncherSelect}
             dock={dock}
             reviewUnavailableReason={reviewUnavailableReason}
+            sideChatAvailable={sideChatAvailable}
           />
         ) : activeTab === null ? null : activeTab.kind === 'side-chat' ? (
           <SideChatSurface parentSessionId={sessionId} sideChatId={activeTab.sideChatId} visible={visible} />
@@ -269,6 +273,7 @@ export function WorkspaceSurface({
           dock={dock}
           initialFocus={initialMenuFocus.current}
           reviewUnavailableReason={reviewUnavailableReason}
+          sideChatAvailable={sideChatAvailable}
           onSelect={selectFromMenu}
           onClose={closeMenu}
         />

desktop/src/pages/ActiveSession.test.tsx

@@ -258,6 +258,34 @@ describe('ActiveSession task polling', () => {
     expect(screen.getByTestId('message-list')).toBe(main)
   })
 
+  it.each([false, true])('offers no side chat in a blank session until it has a conversation (mobile: %s)', (isMobile) => {
+    viewportMocks.isMobile = isMobile
+    const id = `blank-side-parent-${isMobile ? 'mobile' : 'desktop'}`
+    useSettingsStore.setState({ locale: 'en' })
+    useTabStore.setState({ activeTabId: id, tabs: [{ sessionId: id, title: 'Untitled Session', type: 'session', status: 'idle' }] })
+    useSessionStore.setState({ sessions: [{ id, title: 'Untitled Session', messageCount: 0, createdAt: '', modifiedAt: '', projectPath: '/repo', workDir: '/repo', workDirExists: true }] })
+    useChatStore.setState({ sessions: { [id]: { ...createDefaultSessionState(), connectionState: 'connected', historyStatus: 'ready', historyHydrated: true } } })
+    if (!isMobile) useWorkspaceStore.getState().setLayout(id, 'split')
+    render(<ActiveSession sessionId={id} />)
+
+    expect(screen.getByTestId('empty-session-hero')).toBeInTheDocument()
+    expect(screen.queryByRole('button', { name: 'Side chat' })).not.toBeInTheDocument()
+    if (!isMobile) {
+      expect(screen.getByTestId('workspace-launcher-review')).toBeInTheDocument()
+      expect(screen.queryByTestId('workspace-launcher-side-chat')).not.toBeInTheDocument()
+    }
+
+    act(() => useChatStore.setState(state => ({ sessions: { ...state.sessions, [id]: { ...state.sessions[id]!, messages: [{ id: 'u', type: 'user_text', content: 'hi', timestamp: 1 }] } } })))
+
+    expect(screen.queryByTestId('empty-session-hero')).not.toBeInTheDocument()
+    const launcherEntry = screen.queryByTestId('workspace-launcher-side-chat')
+    expect(Boolean(launcherEntry)).toBe(!isMobile)
+    const headerEntry = screen.getAllByRole('button', { name: 'Side chat' }).filter(button => button !== launcherEntry)
+    expect(headerEntry).toHaveLength(1)
+    fireEvent.click(headerEntry[0]!)
+    expect(openSideChat).toHaveBeenCalledWith(id)
+  })
+
   it('can hide a mobile side chat without destroying its temporary tab', () => {
     viewportMocks.isMobile = true
     const id = 'mobile-side-parent'

desktop/src/pages/ActiveSession.tsx

@@ -886,13 +886,18 @@ export function ActiveSession({ sessionId, active = true }: { sessionId?: string
               dock="side"
               cwd={getSessionTerminalCwd(session) ?? ''}
               reviewUnavailableReason={workspaceIsGitRepo === false ? t('workspace.launcher.reviewNeedsGit') : null}
+              sideChatAvailable={!isEmpty}
               visible={active}
             />
           </aside>
         </>
       ) : null}</>}
     >
-          {(isEmpty || isMobileLayout) && (
+          {/*
+            Mobile has no session header, so its side-chat entry lives here. A
+            blank session has nothing for a side chat to fork, so it gets none.
+          */}
+          {isMobileLayout && !isEmpty && (
             <div className="flex justify-end px-4 py-2">
               <IconButton icon={<MessageCircleQuestion size={16} strokeWidth={1.75} aria-hidden="true" />} label={t('sideChat.title')} size="sm"
                 pressed={sideChatOpen} onClick={() => void openSideChat(activeTabId)} />