feat(webui): show forked history boundary

webui/src/tests/message-bubble.test.tsx

@@ -76,8 +76,8 @@ describe("MessageBubble", () => {
 
     expect(row).toHaveClass("ml-auto", "flex");
     expect(pill).toHaveClass("ml-auto", "w-fit", "rounded-[18px]");
-    expect(screen.getByRole("button", { name: "Copy message" })).toBeInTheDocument();
-    expect(screen.queryByRole("button", { name: "Copy reply" })).not.toBeInTheDocument();
+    expect(screen.getByRole("button", { name: "Copy" })).toBeInTheDocument();
+    expect(screen.queryByRole("button", { name: "Fork" })).not.toBeInTheDocument();
   });
 
   it("does not render fork control for user messages", () => {
@@ -91,8 +91,8 @@ describe("MessageBubble", () => {
 
     render(<MessageBubble message={message} onForkFromHere={onForkFromHere} />);
 
-    expect(screen.getByRole("button", { name: "Copy message" })).toBeInTheDocument();
-    expect(screen.queryByRole("button", { name: "Fork from here" })).not.toBeInTheDocument();
+    expect(screen.getByRole("button", { name: "Copy" })).toBeInTheDocument();
+    expect(screen.queryByRole("button", { name: "Fork" })).not.toBeInTheDocument();
   });
 
   it("renders fork control in completed assistant action rows", () => {
@@ -107,7 +107,7 @@ describe("MessageBubble", () => {
 
     render(<MessageBubble message={message} onForkFromHere={onForkFromHere} />);
 
-    fireEvent.click(screen.getByRole("button", { name: "Fork from here" }));
+    fireEvent.click(screen.getByRole("button", { name: "Fork" }));
     expect(onForkFromHere).toHaveBeenCalledTimes(1);
   });
 
@@ -207,11 +207,11 @@ describe("MessageBubble", () => {
 
     render(<MessageBubble message={message} />);
 
-    fireEvent.click(screen.getByRole("button", { name: "Copy reply" }));
+    fireEvent.click(screen.getByRole("button", { name: "Copy" }));
 
     expect(writeText).toHaveBeenCalledWith("I can help with the next step.");
     await waitFor(() =>
-      expect(screen.getByRole("button", { name: "Copied reply" })).toBeInTheDocument(),
+      expect(screen.getByRole("button", { name: "Copied" })).toBeInTheDocument(),
     );
   });
 
@@ -235,11 +235,11 @@ describe("MessageBubble", () => {
     try {
       render(<MessageBubble message={message} />);
 
-      fireEvent.click(screen.getByRole("button", { name: "Copy reply" }));
+      fireEvent.click(screen.getByRole("button", { name: "Copy" }));
 
       await waitFor(() => expect(execCommand).toHaveBeenCalledWith("copy"));
       await waitFor(() =>
-        expect(screen.getByRole("button", { name: "Copied reply" })).toBeInTheDocument(),
+        expect(screen.getByRole("button", { name: "Copied" })).toBeInTheDocument(),
       );
     } finally {
       Reflect.deleteProperty(navigator, "clipboard");
@@ -268,12 +268,12 @@ describe("MessageBubble", () => {
     try {
       render(<MessageBubble message={message} />);
 
-      fireEvent.click(screen.getByRole("button", { name: "Copy reply" }));
+      fireEvent.click(screen.getByRole("button", { name: "Copy" }));
 
       expect(writeText).toHaveBeenCalledWith("Rejected clipboard copy.");
       await waitFor(() => expect(execCommand).toHaveBeenCalledWith("copy"));
       await waitFor(() =>
-        expect(screen.getByRole("button", { name: "Copied reply" })).toBeInTheDocument(),
+        expect(screen.getByRole("button", { name: "Copied" })).toBeInTheDocument(),
       );
     } finally {
       Reflect.deleteProperty(navigator, "clipboard");
@@ -292,7 +292,7 @@ describe("MessageBubble", () => {
 
     render(<MessageBubble message={message} />);
 
-    expect(screen.queryByRole("button", { name: "Copy reply" })).not.toBeInTheDocument();
+    expect(screen.queryByRole("button", { name: "Copy" })).not.toBeInTheDocument();
   });
 
   it("does not show copy when showAssistantCopyAction is false", () => {
@@ -305,7 +305,7 @@ describe("MessageBubble", () => {
 
     render(<MessageBubble message={message} showAssistantCopyAction={false} />);
 
-    expect(screen.queryByRole("button", { name: "Copy reply" })).not.toBeInTheDocument();
+    expect(screen.queryByRole("button", { name: "Copy" })).not.toBeInTheDocument();
   });
 
   it("renders trace messages as collapsible tool groups", () => {

webui/src/tests/thread-messages.test.tsx

@@ -55,6 +55,23 @@ describe("ThreadMessages", () => {
     expect(rows[1]).toHaveClass("mt-4");
   });
 
+  it("renders a fork boundary divider after the copied history", () => {
+    const messages: UIMessage[] = [
+      { id: "u1", role: "user", content: "original", createdAt: 1 },
+      { id: "a1", role: "assistant", content: "answer", createdAt: 2 },
+      { id: "u2", role: "user", content: "branch prompt", createdAt: 3 },
+    ];
+
+    render(
+      <ThreadMessages
+        messages={messages}
+        forkBoundaryMessageCount={2}
+      />,
+    );
+
+    expect(screen.getByText("Forked from history")).toBeInTheDocument();
+  });
+
   it("keeps file edits as their own activity row inside a turn", () => {
     const messages: UIMessage[] = [
       {
@@ -639,7 +656,7 @@ describe("ThreadMessages", () => {
 
     render(<ThreadMessages messages={messages} isStreaming={false} />);
 
-    expect(screen.getAllByRole("button", { name: "Copy reply" })).toHaveLength(1);
+    expect(screen.getAllByRole("button", { name: "Copy" })).toHaveLength(1);
     expect(screen.getByText("final reply")).toBeInTheDocument();
   });
 
@@ -649,7 +666,7 @@ describe("ThreadMessages", () => {
       { id: "a2", role: "assistant", content: "part two", createdAt: 2 },
     ];
     render(<ThreadMessages messages={messages} isStreaming={false} />);
-    expect(screen.getAllByRole("button", { name: "Copy reply" })).toHaveLength(1);
+    expect(screen.getAllByRole("button", { name: "Copy" })).toHaveLength(1);
   });
 
   it("uses turn ids as activity grouping boundaries when available", () => {

webui/src/tests/thread-shell.test.tsx

@@ -758,7 +758,7 @@ describe("ThreadShell", () => {
 
     const targetText = await screen.findByText("answer 100");
     fireEvent.click(within(targetText.closest(".w-full") as HTMLElement).getByRole("button", {
-      name: "Fork from here",
+      name: "Fork",
     }));
 
     await waitFor(() =>
@@ -804,7 +804,7 @@ describe("ThreadShell", () => {
       target: { value: "keep my current draft" },
     });
     fireEvent.click(within(targetText.closest(".w-full") as HTMLElement).getByRole("button", {
-      name: "Fork from here",
+      name: "Fork",
     }));
 
     await waitFor(() => expect(onForkChat).toHaveBeenCalledWith("chat-a", 1));
@@ -864,7 +864,7 @@ describe("ThreadShell", () => {
 
     const targetText = await screen.findByText("answer2");
     fireEvent.click(within(targetText.closest(".w-full") as HTMLElement).getByRole("button", {
-      name: "Fork from here",
+      name: "Fork",
     }));
 
     await waitFor(() => expect(onForkChat).toHaveBeenCalledWith("chat-a", 2));
@@ -962,7 +962,7 @@ describe("ThreadShell", () => {
     );
 
     await screen.findByText("answer1");
-    fireEvent.click(screen.getAllByRole("button", { name: "Fork from here" }).at(-1)!);
+    fireEvent.click(screen.getAllByRole("button", { name: "Fork" }).at(-1)!);
 
     await waitFor(() => expect(onForkChat).toHaveBeenCalledWith("chat-a", 1));
     await act(async () => {

webui/src/tests/useSessions.test.tsx

@@ -230,6 +230,24 @@ describe("useSessions", () => {
     expect(result.current.sessions[0]?.workspaceScope).toEqual(workspaceScope);
   });
 
+  it("keeps a fork title visible while the server session list catches up", async () => {
+    vi.mocked(api.listSessions).mockResolvedValue([]);
+    const client = fakeClient();
+    client.forkChat.mockResolvedValue("chat-fork");
+
+    const { result } = renderHook(() => useSessions(), {
+      wrapper: wrap(client),
+    });
+
+    await waitFor(() => expect(result.current.loading).toBe(false));
+    await act(async () => {
+      await result.current.forkChat("source", 2, "Fork: Original title");
+    });
+
+    expect(client.forkChat).toHaveBeenCalledWith("source", 2, "Fork: Original title");
+    expect(result.current.sessions[0]?.title).toBe("Fork: Original title");
+  });
+
   it("passes through WebUI transcript user media as images and media", async () => {
     vi.mocked(api.fetchWebuiThread).mockResolvedValue({
       schemaVersion: 3,