feat(ui-conversation): wire assistant session forks

packages/client/ui-conversation/src/client/chat/AssistantMarkdown.tsx

@@ -23,6 +23,10 @@ export interface AssistantMarkdownProps {
   interrupted?: boolean | undefined
   /** Unix epoch ms for the finalized IconActions clock; omitted while streaming. */
   time?: number | undefined
+  /** Event sequence used as the fork boundary; omitted while streaming. */
+  seq?: number | undefined
+  /** Fork the session through the turn containing this finalized message. */
+  onFork?: ((seq: number) => void) | undefined
 }
 
 function firstLine(text: string): string {
@@ -60,7 +64,7 @@ function ThinkRow({ text, running }: { text: string; running: boolean }) {
 }
 
 export const AssistantMarkdown = memo(function AssistantMarkdown({
-  blocks, streaming, interrupted, time,
+  blocks, streaming, interrupted, time, seq, onFork,
 }: AssistantMarkdownProps) {
   const last = blocks.length - 1
   // Tool-call heads render as tool rows in the chat view's grouping pass, so
@@ -91,6 +95,7 @@ export const AssistantMarkdown = memo(function AssistantMarkdown({
           text={copyText(blocks)}
           time={time}
           clock="end"
+          onBranch={onFork === undefined || seq === undefined ? undefined : () => { onFork(seq) }}
           className={css.actions}
         />
       )}

packages/client/ui-conversation/src/client/chat/ChatView.tsx

@@ -377,6 +377,8 @@ export function ChatView({ useSession, useSessions, useStore, renderSlot, sessio
           streaming={false}
           interrupted={node.interrupted}
           time={node.time}
+          seq={node.seq}
+          onFork={forkAt}
         />
       )
     }

packages/client/ui-conversation/src/client/chat/MessageIconActions.tsx

@@ -1,5 +1,5 @@
 // Shared IconActions chrome for user and assistant messages: copy live,
-// branch wired through onBranch (stub without it), date-aware clock,
+// branch wired through onBranch, date-aware clock,
 // optional edit stub.
 
 import { useCallback } from 'react'
@@ -19,7 +19,7 @@ export interface MessageIconActionsProps {
   clock: 'start' | 'end'
   /** When true, append the stub edit control (user bubble). */
   edit?: boolean | undefined
-  /** Fork the session at this message; absent leaves the branch control a stub. */
+  /** Fork the session at this message. */
   onBranch?: (() => void) | undefined
   /** Parent layout class composed onto the actions row. */
   className?: string | undefined

packages/client/ui-conversation/tests/chat-view.spec.tsx

@@ -196,6 +196,16 @@ describe('ChatView', () => {
     expect(view.getByText('run a')).toBeTruthy()
   })
 
+  it('forks from both user and finalized assistant message actions at their event seq', () => {
+    const h = makeHarness({ nodes: [user(1, 'question'), assistant(2, 'answer')] })
+    const view = render(<h.ChatView {...h.props} />)
+    const buttons = view.getAllByRole('button', { name: '在新对话中分支' })
+    expect(buttons).toHaveLength(2)
+    fireEvent.click(buttons[0]!)
+    fireEvent.click(buttons[1]!)
+    expect(h.forkAt.mock.calls).toEqual([[1], [2]])
+  })
+
   it('renders assistant Markdown across history, streaming, final, and interrupted states while user text stays literal', () => {
     const markdown = '# Rendered\n\n- **one**\n- `two`'
     const h = makeHarness({ nodes: [user(1, markdown), assistant(2, markdown)] })