diff --git a/frontend/src/features/agents/CustomAgentChatView.test.tsx b/frontend/src/features/agents/CustomAgentChatView.test.tsx
index 6ee04ff..903638a 100644
--- a/frontend/src/features/agents/CustomAgentChatView.test.tsx
+++ b/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 () => ({
diff --git a/frontend/src/features/agents/CustomAgentChatView.tsx b/frontend/src/features/agents/CustomAgentChatView.tsx
index 82dd1fc..9f262da 100644
--- a/frontend/src/features/agents/CustomAgentChatView.tsx
+++ b/frontend/src/features/agents/CustomAgentChatView.tsx
@@ -131,6 +131,7 @@ export function CustomAgentChatView({
   const { agent, system } = useGateways();
   const [turns, setTurns] = useState<ChatTurn[]>([]);
   const [currentSession, setCurrentSession] = useState(sessionId);
+  const [externalSessionId, setExternalSessionId] = useState(sessionId);
   const [draft, setDraft] = useState("");
   const [attachment, setAttachment] = useState<string | null>(null);
   const [opening, setOpening] = useState(false);
@@ -141,6 +142,7 @@ export function CustomAgentChatView({
   sessionRef.current = currentSession;
   const mountedRef = useRef(false);
   const openOrAttachCountRef = useRef(0);
+  const selfEmittedSessionIdRef = useRef<string | null | undefined>(undefined);
   const onSessionIdRef = useRef(onSessionId);
   onSessionIdRef.current = onSessionId;
   const onConversationIdRef = useRef(onConversationId);
@@ -167,6 +169,11 @@ export function CustomAgentChatView({
     if (chunk.kind === "final" || chunk.kind === "error") setBusy(false);
   }, []);
 
+  const publishSessionId = useCallback((nextSessionId: string | null) => {
+    selfEmittedSessionIdRef.current = nextSessionId;
+    onSessionIdRef.current(nextSessionId);
+  }, []);
+
   const reattachStructuredSession = useCallback(
     async (sid: string, options: { applyScrollback?: boolean } = {}) => {
       if (!agent.reattachAgentChat) throw new Error("Structured reattach unavailable");
@@ -249,7 +256,7 @@ export function CustomAgentChatView({
         });
         if (!mountedRef.current) return launched.sessionId;
         setCurrentSession(launched.sessionId);
-        onSessionIdRef.current(launched.sessionId);
+        publishSessionId(launched.sessionId);
         if (launched.assignedConversationId) {
           onConversationIdRef.current(launched.assignedConversationId);
         }
@@ -268,7 +275,7 @@ export function CustomAgentChatView({
             retryAttachNotFound = false;
             if (mountedRef.current) {
               setCurrentSession(null);
-              onSessionIdRef.current(null);
+              publishSessionId(null);
             }
             continue;
           }
@@ -289,6 +296,7 @@ export function CustomAgentChatView({
       nodeId,
       conversationId,
       reattachStructuredSession,
+      publishSessionId,
     ],
   );
 
@@ -297,6 +305,18 @@ export function CustomAgentChatView({
     if (el) el.scrollTop = el.scrollHeight;
   }, [turns]);
 
+  useEffect(() => {
+    if (selfEmittedSessionIdRef.current === sessionId) {
+      console.debug("[ticket149] openOrAttach:self-session-echo:skip", {
+        timestamp: new Date().toISOString(),
+        sessionId,
+      });
+      selfEmittedSessionIdRef.current = undefined;
+      return;
+    }
+    setExternalSessionId(sessionId);
+  }, [sessionId]);
+
   useEffect(() => {
     if (!supported) return;
     let cancelled = false;
@@ -307,19 +327,19 @@ export function CustomAgentChatView({
       console.debug("[ticket149] openOrAttach:start", {
         timestamp: new Date().toISOString(),
         execution,
-        sessionId,
+        sessionId: externalSessionId,
       });
       setOpening(true);
       setError(null);
       try {
-        if (sessionId) {
+        if (externalSessionId) {
           try {
-            await reattachStructuredSession(sessionId, { applyScrollback: true });
+            await reattachStructuredSession(externalSessionId, { applyScrollback: true });
             if (cancelled) return;
             console.debug("[ticket149] openOrAttach:reattach-existing:success", {
               timestamp: new Date().toISOString(),
               execution,
-              sessionId,
+              sessionId: externalSessionId,
             });
             return;
           } catch (e) {
@@ -329,12 +349,12 @@ export function CustomAgentChatView({
             if (!isNotFound(e)) throw e;
             if (!cancelled) {
               setCurrentSession(null);
-              onSessionIdRef.current(null);
+              publishSessionId(null);
             }
             console.debug("[ticket149] openOrAttach:reattach-existing:not-found", {
               timestamp: new Date().toISOString(),
               execution,
-              sessionId,
+              sessionId: externalSessionId,
               error: instrumentationError(e),
             });
           }
@@ -347,13 +367,13 @@ export function CustomAgentChatView({
         console.debug("[ticket149] openOrAttach:recover:success", {
           timestamp: new Date().toISOString(),
           execution,
-          receivedSessionId: sessionId,
+          receivedSessionId: externalSessionId,
         });
       } catch (e) {
         console.error("[ticket149] openOrAttach:error", {
           timestamp: new Date().toISOString(),
           execution,
-          sessionId,
+          sessionId: externalSessionId,
           error: instrumentationError(e),
         });
         if (!cancelled) setError(describe(e));
@@ -368,9 +388,10 @@ export function CustomAgentChatView({
     };
   }, [
     supported,
-    sessionId,
+    externalSessionId,
     reattachStructuredSession,
     recoverStructuredSession,
+    publishSessionId,
   ]);
 
   const canSend = useMemo(
@@ -408,7 +429,7 @@ export function CustomAgentChatView({
       if (isNotFound(e)) {
         try {
           setCurrentSession(null);
-          onSessionIdRef.current(null);
+          publishSessionId(null);
           const recoveredSession = await recoverStructuredSession({
             applyScrollback: false,
             retryAttachNotFound: true,
@@ -440,7 +461,7 @@ export function CustomAgentChatView({
     } catch (e) {
       if (isNotFound(e)) {
         setCurrentSession(null);
-        onSessionIdRef.current(null);
+        publishSessionId(null);
         setTurns((prev) => [...prev, { role: "tool", label: "Session déjà fermée." }]);
         return;
       }