fix(chat): ignore self-emitted custom session echoes

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/features/agents/CustomAgentChatView.test.tsx

@@ -1,4 +1,5 @@
 import { fireEvent, render, screen, waitFor } from "@testing-library/react";
+import { useState } from "react";
 import { describe, expect, it, vi } from "vitest";
 
 import { DIProvider } from "@/app/di";
@@ -151,6 +152,63 @@ describe("CustomAgentChatView", () => {
     expect(screen.queryByText(/structured session gone/)).toBeNull();
   });
 
+  it("does not reopen when the parent echoes a launched session id", async () => {
+    const agent = {
+      launchAgentChat: vi.fn(async () => ({
+        sessionId: "chat-session-echo",
+        assignedConversationId: "conversation-2",
+      })),
+      reattachAgentChat: vi.fn(async (sessionId: string) => ({
+        sessionId,
+        scrollback: [],
+      })),
+      sendAgentChat: vi.fn(() => new Promise<void>(() => {})),
+      cancelAgentChat: vi.fn(async () => {}),
+      closeAgentChat: vi.fn(async () => {}),
+    };
+    const onSessionId = vi.fn();
+
+    function EchoingParent() {
+      const [echoedSessionId, setEchoedSessionId] = useState<string | null>(null);
+      return (
+        <DIProvider
+          gateways={{
+            agent,
+            system: { pickFile: vi.fn(async () => null) },
+          } as unknown as Gateways}
+        >
+          <CustomAgentChatView
+            projectId="project-1"
+            agentId="agent-1"
+            agentName="Worker"
+            profile={profile}
+            cwd="/repo"
+            nodeId="node-1"
+            sessionId={echoedSessionId}
+            conversationId="conversation-1"
+            onSessionId={(nextSessionId) => {
+              onSessionId(nextSessionId);
+              setEchoedSessionId(nextSessionId);
+            }}
+            onConversationId={vi.fn()}
+          />
+        </DIProvider>
+      );
+    }
+
+    render(<EchoingParent />);
+
+    await waitFor(() =>
+      expect(onSessionId).toHaveBeenCalledWith("chat-session-echo"),
+    );
+    await waitFor(() => expect(agent.launchAgentChat).toHaveBeenCalledTimes(1));
+    await waitFor(() => expect(agent.reattachAgentChat).toHaveBeenCalledTimes(1));
+    await new Promise((resolve) => setTimeout(resolve, 20));
+
+    expect(agent.launchAgentChat).toHaveBeenCalledTimes(1);
+    expect(agent.reattachAgentChat).toHaveBeenCalledTimes(1);
+  });
+
   it("recovers and retries the prompt when send reports NOT_FOUND", async () => {
     const agent = {
       launchAgentChat: vi.fn(async () => ({