diff --git a/canvas/src/components/tabs/chat/hooks/__tests__/useChatSend.originMessageId.test.tsx b/canvas/src/components/tabs/chat/hooks/__tests__/useChatSend.originMessageId.test.tsx
new file mode 100644
index 000000000..f70d0ae30
--- /dev/null
+++ b/canvas/src/components/tabs/chat/hooks/__tests__/useChatSend.originMessageId.test.tsx
@@ -0,0 +1,92 @@
+// @vitest-environment jsdom
+//
+// core#2713 — origin-device duplicate user bubble.
+//
+// Mechanism: useChatSend optimistically appends a user message with id X,
+// then POSTs /a2a with message.messageId = crypto.randomUUID() (id Y).
+// The server broadcasts USER_MESSAGE with id Y, and ChatTab dedupes by id
+// via appendMessageDedupedById. Because X ≠ Y, the origin device renders
+// both the optimistic bubble and the server echo.
+//
+// Fix: reuse the optimistic message id as the outbound A2A messageId so
+// the echo is collapsed on the origin device while other devices still
+// append normally.
+
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { renderHook, act } from "@testing-library/react";
+
+const apiPostMock = vi.fn<
+  (url: string, body?: unknown, opts?: unknown) => Promise<unknown>
+>();
+vi.mock("@/lib/api", () => ({
+  api: {
+    post: (url: string, body?: unknown, opts?: unknown) =>
+      apiPostMock(url, body, opts),
+    get: vi.fn(),
+  },
+}));
+vi.mock("../../uploads", () => ({
+  uploadChatFiles: vi.fn(),
+  FileTooLargeError: class FileTooLargeError extends Error {},
+}));
+
+import { useChatSend } from "../useChatSend";
+
+beforeEach(() => {
+  apiPostMock.mockReset();
+});
+
+describe("useChatSend — origin-device message id deduplication — core#2713", () => {
+  it("reuses the optimistic user message id as the outbound A2A messageId", async () => {
+    apiPostMock.mockResolvedValueOnce({ status: "queued", delivery_mode: "poll" });
+
+    const onUserMessage = vi.fn();
+    const { result } = renderHook(() =>
+      useChatSend("ws-origin-dedup", {
+        getHistoryMessages: () => [],
+        onUserMessage,
+      }),
+    );
+
+    await act(async () => {
+      await result.current.sendMessage("What is the weather?");
+      await Promise.resolve();
+    });
+
+    expect(onUserMessage).toHaveBeenCalledTimes(1);
+    const optimisticMsg = onUserMessage.mock.calls[0][0] as { id: string };
+    expect(optimisticMsg.id).toBeTruthy();
+
+    expect(apiPostMock).toHaveBeenCalledTimes(1);
+    const body = apiPostMock.mock.calls[0][1] as {
+      params: { message: { messageId: string } };
+    };
+    expect(body.params.message.messageId).toBe(optimisticMsg.id);
+  });
+
+  it("does not mint a fresh random UUID for the A2A payload", async () => {
+    apiPostMock.mockResolvedValueOnce({ status: "queued", delivery_mode: "poll" });
+
+    const onUserMessage = vi.fn();
+    const { result } = renderHook(() =>
+      useChatSend("ws-no-random-uuid", {
+        getHistoryMessages: () => [],
+        onUserMessage,
+      }),
+    );
+
+    await act(async () => {
+      await result.current.sendMessage("no duplicate please");
+      await Promise.resolve();
+    });
+
+    const optimisticMsg = onUserMessage.mock.calls[0][0] as { id: string };
+    const body = apiPostMock.mock.calls[0][1] as {
+      params: { message: { messageId: string } };
+    };
+    // The critical regression guard: if these diverge, appendMessageDedupedById
+    // cannot collapse the optimistic bubble and the WS USER_MESSAGE echo.
+    expect(body.params.message.messageId).not.toBe(crypto.randomUUID()); // always different
+    expect(body.params.message.messageId).toBe(optimisticMsg.id);
+  });
+});
diff --git a/canvas/src/components/tabs/chat/hooks/useChatSend.ts b/canvas/src/components/tabs/chat/hooks/useChatSend.ts
index cf124b602..6237ad52d 100644
--- a/canvas/src/components/tabs/chat/hooks/useChatSend.ts
+++ b/canvas/src/components/tabs/chat/hooks/useChatSend.ts
@@ -219,7 +219,7 @@ export function useChatSend(workspaceId: string, options: UseChatSendOptions) {
             params: {
               message: {
                 role: "user",
-                messageId: crypto.randomUUID(),
+                messageId: userMsg.id,
                 parts,
               },
               metadata: { history },