feat(web): add nested subagent conversations

packages/client/ui-conversation/src/client/apply.ts

@@ -165,7 +165,10 @@ export function apply(ctx: Context): void {
   // the resident parent keeps Hero and composer layout identity stable.
   slots.register({
     name: 'conversation.session',
-    children: { 'conversation.view': { kind: 'list', scope: 'session' } },
+    children: {
+      'conversation.view': { kind: 'list', scope: 'session' },
+      'conversation.session.header.actions': { kind: 'list', scope: 'session' },
+    },
     store: chatStore,
     inject: (sessionId: SessionId, _actions: BoundActions<typeof chatStore>): ConversationSessionInjected => ({
       views: {

packages/client/ui-conversation/src/client/contract/slots.ts

@@ -17,6 +17,8 @@ declare module '@deepseek-ai/dsh-client-ui-slots' {
      * remounted when the current session id changes.
      */
     'conversation.session': { kind: 'single'; scope: 'session'; owner: ConversationSessionOwnerProps }
+    /** Session-header actions contributed by feature plugins. */
+    'conversation.session.header.actions': { kind: 'list'; scope: 'session'; owner: ConversationHeaderActionOwnerProps }
     /**
      * The conversation view ring: one list entry per view tab (chat here;
      * trajectory/waterfall from ui-trajectory), rendered one-at-a-time by
@@ -135,6 +137,9 @@ export interface ConversationSessionOwnerProps {
   wrapActiveBody?: (view: ReactNode) => ReactNode
 }
 
+/** Header actions derive their state from the standard session/global kit. */
+export interface ConversationHeaderActionOwnerProps {}
+
 /**
  * The input-region slot currency (plan §1.4): dock/left/right entries read
  * the conversation snapshot and the live input state as owner props (both
@@ -329,6 +334,8 @@ export type ComposerBarProps =
  */
 export interface ComposerChainProps {
   interactions: readonly PendingInteraction[]
+  /** A catalog-addressed child whose exact parent Agent is unavailable. */
+  subagentReadOnly: boolean
 }
 
 /**
@@ -350,7 +357,7 @@ export type ConversationSlotProps =
 /** Full strict-session content props: per-session store, view ring, callbacks, and the locale seat. */
 export type ConversationSessionSlotProps =
   PropsRuntime<'conversation.session'>
-  & PropsRenderSlots<'conversation.view'>
+  & PropsRenderSlots<'conversation.view' | 'conversation.session.header.actions'>
   & PropsStore<ChatStore>
   & ConversationSessionInjected
 

packages/client/ui-conversation/src/client/skeleton/ConversationRoot.module.css

@@ -26,6 +26,8 @@
 .titleRow {
   display: flex;
   align-items: center;
+  justify-content: space-between;
+  gap: 10px;
   min-height: 32px;
 }
 
@@ -43,6 +45,13 @@
   white-space: nowrap;
 }
 
+.headerActions {
+  display: flex;
+  flex: none;
+  align-items: center;
+  gap: 8px;
+}
+
 /* figma Tab_Group 34:11441: 35px strip, gap 36, pad-left 8, tabs bottom-aligned. */
 .tabs {
   display: flex;

packages/client/ui-conversation/src/client/skeleton/ConversationRoot.tsx

@@ -19,6 +19,7 @@ export function ConversationRoot({
   const openState = useSession(s => s.openState)
   const composerPhase = useSession(s => s.composerPhase)
   const pending = useSession(s => s.pending) ?? []
+  const subagentReadOnly = useSession(s => s?.subagent?.parentAvailable === false) ?? false
   const session = useSession(s => s)
   const inputState = useInput(s => s)
   const cwd = useSessions(s => sessionId === undefined ? undefined : s.byId[sessionId]?.cwd)
@@ -153,7 +154,7 @@ export function ConversationRoot({
   const phase = settling ? 'settling' : hero ? 'hero' : 'active'
   const composer = renderSlotChain(
     'conversation.composer',
-    { interactions: pending },
+    { interactions: pending, subagentReadOnly },
     { fallback: composerBar, overlay: true },
   )
 

packages/client/ui-conversation/src/client/skeleton/ConversationSession.tsx

@@ -57,6 +57,9 @@ export function ConversationSession({
           <>
             <div className={css.titleRow}>
               <h1 className={css.sessionTitle}>{title}</h1>
+              <div className={css.headerActions}>
+                {renderSlot('conversation.session.header.actions', {})}
+              </div>
             </div>
             {tabs.length > 1 && (
               <div className={css.tabs} role="tablist">

packages/client/ui-conversation/src/client/skeleton/InputBar.tsx

@@ -44,6 +44,7 @@ export function InputBar({
   const commandMenuOpen = useMenuLauncher(source => source === 'command')
   const promptError = useSession(s => s.promptError) ?? null
   const running = useSession(s => s.running) ?? false
+  const subagent = useSession(s => s.subagent) ?? null
   const removed = useSession(s => s.removed) ?? false
   // Plan mode swaps the textarea placeholder (the projection is the folded
   // host value; owner-prop placeholders — hero, session-unavailable — win).
@@ -283,10 +284,11 @@ export function InputBar({
     if (el !== null) toggleCommandMenu?.(selectionOf(el))
   }
 
-  const primaryLabel = running ? t('input.stop') : t('input.send')
+  const ordinary = subagent === null
+  const primaryLabel = running && ordinary ? t('input.stop') : t('input.send')
   const onPrimary = (): void => {
     if (inputActions === undefined || stop === undefined) return // absent machine: the button is disabled
-    if (running) {
+    if (running && ordinary) {
       stop()
       return
     }