canvas/src/components/tabs/chat/hooks/__tests__/useChatSend.multiSend.test.tsx

@@ -82,4 +82,38 @@ describe("useChatSend — multi-send (core#2697 feature 2)", () => {
     expect(onUserMessage).not.toHaveBeenCalled();
     expect(apiPostMock).not.toHaveBeenCalled();
   });
+  it("treats a Cloudflare 524 gateway timeout as 'still processing' (no unreachable banner)", async () => {
+    // A long turn outlives CF's ~100s edge limit → api.post throws an Error
+    // with .status=524. The agent is still working; reply arrives via WS.
+    const err = Object.assign(new Error("API POST /workspaces/ws-1/a2a: 524 "), { status: 524 });
+    apiPostMock.mockRejectedValueOnce(err);
+    const onUserMessage = vi.fn();
+    const { result } = renderHook(() =>
+      useChatSend("ws-1", { getHistoryMessages: () => [], onUserMessage }),
+    );
+    await act(async () => {
+      await result.current.sendMessage("long migrate task");
+      await Promise.resolve(); await Promise.resolve();
+    });
+    // Spinner stays (sending true), NO error banner.
+    expect(result.current.sending).toBe(true);
+    expect(result.current.error).toBeNull();
+  });
+
+  it("a Cloudflare 522 (couldn't connect to origin) DOES surface the unreachable banner", async () => {
+    // CR2 distinction: 522 = CF couldn't establish a connection to the origin
+    // = genuinely unreachable. Unlike 524 (accepted + slow), 522 must NOT be
+    // swallowed — show the error so the user knows the message didn't land.
+    const err = Object.assign(new Error("API POST /workspaces/ws-1/a2a: 522 "), { status: 522 });
+    apiPostMock.mockRejectedValueOnce(err);
+    const { result } = renderHook(() =>
+      useChatSend("ws-1", { getHistoryMessages: () => [] }),
+    );
+    await act(async () => {
+      await result.current.sendMessage("hi");
+      await Promise.resolve(); await Promise.resolve();
+    });
+    expect(result.current.error).toMatch(/unreachable/i);
+  });
+
 });

canvas/src/components/tabs/chat/hooks/useChatSend.ts

@@ -322,7 +322,20 @@ export function useChatSend(workspaceId: string, options: UseChatSendOptions) {
           const isClientTimeout =
             e !== null && typeof e === "object" &&
             "name" in e && (e as { name: unknown }).name === "TimeoutError";
-          if (isClientTimeout) {
+          // CLOUDFLARE 524 ≠ UNREACHABLE (jrs-auto, 2026-06-13). The canvas→agent
+          // A2A POST is held open for the whole turn; a turn that runs longer
+          // than Cloudflare's ~100s edge limit gets a 524 ("A Timeout Occurred")
+          // — the origin ACCEPTED the request and is still processing it (the
+          // agent is visibly running tools), and its reply arrives via the
+          // AGENT_MESSAGE WebSocket event, exactly like the client-timeout case.
+          // ONLY 524: per CR2, 522 ("Connection Timed Out" — CF couldn't even
+          // connect to the origin) and 504 mean the request was NOT accepted /
+          // the origin is genuinely unreachable, so those MUST still surface the
+          // error banner. Don't conflate "accepted + slow" (524) with "couldn't
+          // connect" (522).
+          const status = (e as { status?: number } | null)?.status;
+          const isCloudflareHeldRequest = status === 524;
+          if (isClientTimeout || isCloudflareHeldRequest) {
             return; // delivered; reply (and guard release) arrives via WS
           }
           releaseSendGuards();

canvas/src/lib/api.ts

@@ -167,7 +167,12 @@ async function request<T>(
         if (err instanceof PlatformUnavailableError) throw err;
       }
     }
-    throw new Error(`API ${method} ${path}: ${res.status} ${text}`);
+    const apiErr = new Error(`API ${method} ${path}: ${res.status} ${text}`);
+    // Attach the HTTP status so callers can branch without parsing the
+    // message (e.g. useChatSend treats a Cloudflare 524/522/504 on a held
+    // long A2A turn as "still processing", not "agent unreachable").
+    (apiErr as Error & { status?: number }).status = res.status;
+    throw apiErr;
   }
   return res.json();
 }