canvas/src/components/tabs/ChatTab.tsx

@@ -243,6 +243,22 @@ function MyChatPanel({ workspaceId, data }: Props) {
     }
   }, [data.status, clearSendError]);
 
+  // Clear any stale "Failed to send — agent may be unreachable" banner the
+  // moment the agent is demonstrably WORKING (core#2697). `thinking` is true
+  // when the user's send is in flight OR the workspace heartbeat reports an
+  // in-flight task — either way the agent is reachable, so an "unreachable"
+  // banner is self-contradictory (reported: banner shown beside a live
+  // "●●● 102s" timer + streaming tool calls on a long poll-mode turn).
+  // #2736 only cleared on a reply LANDING; this also clears the instant the
+  // agent starts/continues working, so the banner can't linger through a
+  // multi-minute turn that hasn't replied yet.
+  useEffect(() => {
+    if (thinking) {
+      setError(null);
+      clearSendError();
+    }
+  }, [thinking, clearSendError]);
+
   // Scroll behavior across messages updates:
   //  - Prepend (loadOlder landed)  → restore the user's saved
   //    distance-from-bottom so their reading position is unchanged.

canvas/src/components/tabs/__tests__/ChatTab.errorClearOnReply.test.tsx

@@ -75,4 +75,14 @@ describe("ChatTab — stale error banner clears on a successful reply (core#2697
     act(() => { captured.onSendComplete?.(); });
     expect(clearErrorSpy).toHaveBeenCalled();
   });
+
+  it("clears the 'unreachable' banner while the agent is THINKING (currentTask set), before any reply", () => {
+    // The reported bug: banner shown beside a live "●●● 102s" timer on a long
+    // poll-mode turn that hadn't replied yet. data.currentTask set => thinking
+    // => the agent is reachable => the unreachable banner must clear on its own.
+    const busy = { status: "online" as const, runtime: "claude-code", currentTask: "downloading assets" } as unknown as Parameters<typeof ChatTab>[0]["data"];
+    render(<ChatTab workspaceId="ws-thinking" data={busy} />);
+    // Mount with currentTask set => the thinking-clears-error effect fires.
+    expect(clearErrorSpy).toHaveBeenCalled();
+  });
 });