canvas/src/components/mobile/MobileChat.tsx

@@ -767,7 +767,12 @@ export function MobileChat({
           <button
             type="button"
             onClick={() => fileInputRef.current?.click()}
-            disabled={!reachable || sending || uploading}
+            // Multi-send parity (core#2726 / CR2 #2762): the attach button
+            // must NOT disable while a send is in flight, so the user can add
+            // attachments to a follow-up message while the agent is still
+            // working. Keep the uploading gate (single concurrent upload) and
+            // the reachable gate (offline agent).
+            disabled={!reachable || uploading}
             aria-label="Attach"
             className="focus:outline-none focus-visible:ring-2 focus-visible:ring-emerald-500 focus-visible:ring-offset-2 focus-visible:ring-offset-zinc-100 dark:focus-visible:ring-offset-zinc-900"
             style={{
@@ -775,14 +780,14 @@ export function MobileChat({
               height: 32,
               borderRadius: 999,
               border: "none",
-              cursor: reachable && !sending && !uploading ? "pointer" : "not-allowed",
+              cursor: reachable && !uploading ? "pointer" : "not-allowed",
               background: "transparent",
               color: p.text3,
               flexShrink: 0,
               display: "flex",
               alignItems: "center",
               justifyContent: "center",
-              opacity: !reachable || sending || uploading ? 0.4 : 1,
+              opacity: !reachable || uploading ? 0.4 : 1,
             }}
           >
             {Icons.attach({ size: 16 })}

canvas/src/components/mobile/__tests__/MobileChat.test.tsx

@@ -678,8 +678,11 @@ describe("MobileChat — thinking indicator (core#2720/#2745 parity)", () => {
 });
 
 describe("MobileChat — multi-send tap path (CR2 #2762)", () => {
-  it("Send button stays ENABLED during an in-flight send (tap multi-send)", async () => {
+  beforeEach(() => {
     mockStoreState.nodes = [onlineNode];
+  });
+
+  it("Send button stays ENABLED during an in-flight send (tap multi-send)", async () => {
     // First send hangs → sending stays true.
     vi.spyOn(api, "post").mockReturnValueOnce(new Promise(() => {}));
     const { container } = renderChat(mockAgentId);
@@ -698,4 +701,65 @@ describe("MobileChat — multi-send tap path (CR2 #2762)", () => {
     });
     expect(sendBtn().disabled).toBe(false);
   });
+
+  it("Attach button stays ENABLED during an in-flight send (core#2762 follow-up)", async () => {
+    // First send hangs → sending stays true.
+    vi.spyOn(api, "post").mockReturnValueOnce(new Promise(() => {}));
+    const { container } = renderChat(mockAgentId);
+    const ta = container.querySelector("textarea") as HTMLTextAreaElement;
+    const sendBtn = container.querySelector('[aria-label="Send"]') as HTMLButtonElement;
+    const attachBtn = container.querySelector('[aria-label="Attach"]') as HTMLButtonElement;
+
+    await act(async () => {
+      fireEvent.change(ta, { target: { value: "first" } });
+    });
+    await act(async () => {
+      sendBtn.click();
+    });
+
+    // Attach must remain usable while the send is in flight.
+    expect(attachBtn.disabled).toBe(false);
+
+    // Selecting a file while sending should add it to the pending list.
+    const fileInput = container.querySelector('input[type="file"]') as HTMLInputElement;
+    const file = new File(["hello"], "note.txt", { type: "text/plain" });
+    await act(async () => {
+      fireEvent.change(fileInput, { target: { files: [file] } });
+    });
+    expect(container.textContent ?? "").toContain("note.txt");
+  });
+
+  it("clears the send-error banner when a follow-up send starts (multi-send banner-clear)", async () => {
+    const postSpy = vi.spyOn(api, "post");
+    // First send fails → error banner.
+    postSpy.mockRejectedValueOnce(new Error("boom"));
+    // Second send succeeds → banner must clear.
+    postSpy.mockResolvedValueOnce({ result: { parts: [] } });
+
+    const { container } = renderChat(mockAgentId);
+    const ta = container.querySelector("textarea") as HTMLTextAreaElement;
+    const sendBtn = container.querySelector('[aria-label="Send"]') as HTMLButtonElement;
+
+    await act(async () => {
+      fireEvent.change(ta, { target: { value: "first" } });
+    });
+    await act(async () => {
+      sendBtn.click();
+    });
+    await waitFor(() => {
+      expect(container.textContent ?? "").toContain("unreachable");
+    });
+
+    // Start a follow-up send; the banner should clear as soon as the new
+    // send is dispatched (send() calls clearError before awaiting the POST).
+    await act(async () => {
+      fireEvent.change(ta, { target: { value: "second" } });
+    });
+    await act(async () => {
+      sendBtn.click();
+    });
+    await waitFor(() => {
+      expect(container.textContent ?? "").not.toContain("unreachable");
+    });
+  });
 });