diff --git a/canvas/src/components/tabs/chat/hooks/__tests__/useChatSend.test.tsx b/canvas/src/components/tabs/chat/hooks/__tests__/useChatSend.test.tsx
new file mode 100644
index 000000000..796104616
--- /dev/null
+++ b/canvas/src/components/tabs/chat/hooks/__tests__/useChatSend.test.tsx
@@ -0,0 +1,209 @@
+// @vitest-environment jsdom
+/**
+ * Tests for useChatSend — the canvas user→agent send hook.
+ *
+ * Behavioural focus: the poll-mode ("queued") path. When the target
+ * workspace is an external / MCP-registered agent (delivery_mode=poll,
+ * e.g. an operator laptop running the molecule MCP channel), the
+ * platform's POST /workspaces/:id/a2a returns a synthetic
+ * {status:"queued", delivery_mode:"poll"} envelope IMMEDIATELY with no
+ * reply — the real reply arrives later over the AGENT_MESSAGE
+ * WebSocket push.
+ *
+ * Pre-fix the hook treated that synthetic envelope as a terminal
+ * response and called releaseSendGuards() → `sending` went false the
+ * instant the POST returned → the "agent is working" indicator
+ * vanished and the external turn looked dead. This suite pins the
+ * fixed contract:
+ *
+ *   - a real reply still clears `sending` (regression guard)
+ *   - a poll "queued" envelope KEEPS `sending` true (no terminal
+ *     clear) so the existing thinking indicator persists
+ *   - the eventual reply path (releaseSendGuards, the same call the
+ *     AGENT_MESSAGE WS push makes via useChatSocket) clears it
+ *   - an offline poll agent that never replies eventually surfaces an
+ *     honest error instead of an infinite spinner
+ *
+ * Plus pure-function coverage for the poll-envelope detector.
+ *
+ * Root cause: workspace-server a2a_proxy.go:402 poll-mode
+ * short-circuit returns {status:"queued"} synchronously.
+ */
+import {
+  describe,
+  it,
+  expect,
+  vi,
+  beforeEach,
+  afterEach,
+  type Mock,
+} from "vitest";
+import { act, renderHook, cleanup } from "@testing-library/react";
+
+const { mockApiPost } = vi.hoisted(() => ({ mockApiPost: vi.fn() }));
+
+vi.mock("@/lib/api", () => ({
+  api: { post: mockApiPost },
+}));
+
+vi.mock("../uploads", () => ({
+  uploadChatFiles: vi.fn(),
+}));
+
+// Import AFTER mocks.
+import {
+  useChatSend,
+  isPollQueuedResponse,
+  extractReplyText,
+  POLL_QUEUED_REPLY_TIMEOUT_MS,
+} from "../useChatSend";
+
+const flush = () => act(async () => { await Promise.resolve(); });
+
+describe("isPollQueuedResponse", () => {
+  it("is true only for the synthetic poll-mode queued envelope", () => {
+    expect(isPollQueuedResponse({ status: "queued", delivery_mode: "poll" })).toBe(true);
+  });
+
+  it("is false for a real agent reply", () => {
+    expect(
+      isPollQueuedResponse({ result: { parts: [{ kind: "text", text: "hi" }] } }),
+    ).toBe(false);
+  });
+
+  it("is false for null / undefined / partial shapes", () => {
+    expect(isPollQueuedResponse(null)).toBe(false);
+    expect(isPollQueuedResponse(undefined)).toBe(false);
+    // status=queued without delivery_mode=poll is NOT the poll envelope
+    // — don't accidentally swallow a real reply that happens to carry
+    // an unrelated status field.
+    expect(isPollQueuedResponse({ status: "queued" })).toBe(false);
+    expect(isPollQueuedResponse({ delivery_mode: "poll" })).toBe(false);
+  });
+});
+
+describe("extractReplyText (regression guard — unchanged by fix)", () => {
+  it("collects text parts from result", () => {
+    expect(
+      extractReplyText({ result: { parts: [{ kind: "text", text: "hello" }] } }),
+    ).toBe("hello");
+  });
+  it("returns empty for the poll-queued envelope", () => {
+    expect(extractReplyText({ status: "queued", delivery_mode: "poll" })).toBe("");
+  });
+});
+
+describe("useChatSend — poll-mode in-progress state", () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+    mockApiPost.mockReset();
+  });
+  afterEach(() => {
+    vi.runOnlyPendingTimers();
+    vi.useRealTimers();
+    cleanup();
+  });
+
+  const setup = () => {
+    const onUserMessage = vi.fn();
+    const onAgentMessage = vi.fn();
+    const { result } = renderHook(() =>
+      useChatSend("ws-ext-1", {
+        getHistoryMessages: () => [],
+        onUserMessage,
+        onAgentMessage,
+      }),
+    );
+    return { result, onUserMessage, onAgentMessage };
+  };
+
+  it("a real reply clears `sending` (regression guard)", async () => {
+    mockApiPost.mockResolvedValue({
+      result: { parts: [{ kind: "text", text: "real reply" }] },
+    });
+    const { result, onAgentMessage } = setup();
+
+    await act(async () => {
+      void result.current.sendMessage("hi");
+    });
+    await flush();
+
+    expect(onAgentMessage).toHaveBeenCalledTimes(1);
+    expect(result.current.sending).toBe(false);
+  });
+
+  it("keeps `sending` true on a poll 'queued' envelope (no terminal clear)", async () => {
+    mockApiPost.mockResolvedValue({ status: "queued", delivery_mode: "poll" });
+    const { result, onAgentMessage } = setup();
+
+    await act(async () => {
+      void result.current.sendMessage("hi external agent");
+    });
+    await flush();
+
+    // The POST resolved, but it was only a queued ack — the indicator
+    // must stay up and no agent bubble should be rendered yet.
+    expect(result.current.sending).toBe(true);
+    expect(onAgentMessage).not.toHaveBeenCalled();
+    expect(result.current.error).toBeNull();
+  });
+
+  it("releaseSendGuards (the AGENT_MESSAGE-push path) clears the poll in-progress state", async () => {
+    mockApiPost.mockResolvedValue({ status: "queued", delivery_mode: "poll" });
+    const { result } = setup();
+
+    await act(async () => {
+      void result.current.sendMessage("hi");
+    });
+    await flush();
+    expect(result.current.sending).toBe(true);
+
+    // Simulate the terminal AGENT_MESSAGE WebSocket push arriving:
+    // useChatSocket's onAgentMessage / onSendComplete call
+    // releaseSendGuards. That must clear the in-progress state AND the
+    // safety timer (asserted by the next test).
+    act(() => {
+      result.current.releaseSendGuards();
+    });
+    expect(result.current.sending).toBe(false);
+  });
+
+  it("surfaces an honest error if a poll agent never replies (safety timeout)", async () => {
+    mockApiPost.mockResolvedValue({ status: "queued", delivery_mode: "poll" });
+    const { result } = setup();
+
+    await act(async () => {
+      void result.current.sendMessage("hi");
+    });
+    await flush();
+    expect(result.current.sending).toBe(true);
+
+    act(() => {
+      vi.advanceTimersByTime(POLL_QUEUED_REPLY_TIMEOUT_MS + 1000);
+    });
+
+    expect(result.current.sending).toBe(false);
+    expect(result.current.error).toMatch(/queued/i);
+  });
+
+  it("does NOT fire the safety error when the reply arrives before timeout", async () => {
+    mockApiPost.mockResolvedValue({ status: "queued", delivery_mode: "poll" });
+    const { result } = setup();
+
+    await act(async () => {
+      void result.current.sendMessage("hi");
+    });
+    await flush();
+
+    // Reply arrives (releaseSendGuards) well before the timeout.
+    act(() => {
+      result.current.releaseSendGuards();
+    });
+    act(() => {
+      vi.advanceTimersByTime(POLL_QUEUED_REPLY_TIMEOUT_MS + 1000);
+    });
+
+    expect(result.current.error).toBeNull();
+    expect(result.current.sending).toBe(false);
+  });
+});
diff --git a/canvas/src/components/tabs/chat/hooks/useChatSend.ts b/canvas/src/components/tabs/chat/hooks/useChatSend.ts
index dd9951b55..e0efd2614 100644
--- a/canvas/src/components/tabs/chat/hooks/useChatSend.ts
+++ b/canvas/src/components/tabs/chat/hooks/useChatSend.ts
@@ -1,6 +1,6 @@
 "use client";
 
-import { useCallback, useRef, useState } from "react";
+import { useCallback, useEffect, useRef, useState } from "react";
 import { api } from "@/lib/api";
 import { uploadChatFiles } from "../uploads";
 import { createMessage, type ChatMessage, type ChatAttachment } from "../types";
@@ -22,8 +22,42 @@ interface A2AResponse {
     parts?: A2APart[];
     artifacts?: Array<{ parts: A2APart[] }>;
   };
+  /** Synthetic poll-mode envelope. The platform returns this
+   *  immediately (HTTP 200) when the target workspace is registered
+   *  delivery_mode=poll — an external / MCP-registered agent with no
+   *  public URL (e.g. an operator's laptop running the molecule MCP
+   *  channel). The request has only been QUEUED into activity_logs;
+   *  the agent will pick it up on its next poll and the real reply
+   *  arrives asynchronously over the AGENT_MESSAGE WebSocket push
+   *  (consumed by useChatSocket). See workspace-server
+   *  a2a_proxy.go:402 (poll-mode short-circuit) and
+   *  a2a_proxy_helpers.go:516 (logA2AReceiveQueued). */
+  status?: string;
+  delivery_mode?: string;
 }
 
+/** True when `resp` is the platform's synthetic poll-mode "queued"
+ *  envelope rather than a real agent reply. For these the send is
+ *  acknowledged-but-pending: the user's message landed and the agent
+ *  is working, but there is no reply yet — the terminal AGENT_MESSAGE
+ *  push will arrive later over the WebSocket. Treating this as a
+ *  terminal response (the pre-fix behaviour) cleared the "agent is
+ *  working" indicator the instant the POST returned, so an external
+ *  workspace turn looked dead even though work had not started. */
+export function isPollQueuedResponse(resp: A2AResponse | null | undefined): boolean {
+  return !!resp && resp.status === "queued" && resp.delivery_mode === "poll";
+}
+
+/** Hard ceiling on how long the "agent is working" indicator stays up
+ *  for a poll-mode turn with no reply. The terminal AGENT_MESSAGE push
+ *  normally clears it well before this. The cap exists so a poll-mode
+ *  workspace that is offline / never consumes its queue doesn't pin a
+ *  spinner forever — at which point we surface an honest, actionable
+ *  error instead of an opaque dead spinner. Generous because poll
+ *  agents (an operator laptop) can legitimately take minutes to wake,
+ *  poll, and respond; the goal is "eventually honest", not fail-fast. */
+export const POLL_QUEUED_REPLY_TIMEOUT_MS = 15 * 60 * 1000;
+
 export function extractReplyText(resp: A2AResponse): string {
   const collect = (parts: A2APart[] | undefined): string => {
     if (!parts) return "";
@@ -59,14 +93,29 @@ export function useChatSend(workspaceId: string, options: UseChatSendOptions) {
   const sendInFlightRef = useRef(false);
   const sendingFromAPIRef = useRef(false);
   const sendTokenRef = useRef(0);
+  // Safety-net timer armed only for poll-mode ("queued") turns: the
+  // POST returns immediately with no reply, so the normal
+  // POST-resolves-→-clear-spinner path can't drive the indicator. The
+  // terminal AGENT_MESSAGE WebSocket push clears it via
+  // releaseSendGuards (which also clears this timer); the timer is the
+  // backstop for an offline poll agent that never consumes its queue.
+  const pollTimeoutRef = useRef<ReturnType<typeof setTimeout> | null>(null);
   const optionsRef = useRef(options);
   optionsRef.current = options;
 
+  const clearPollTimeout = useCallback(() => {
+    if (pollTimeoutRef.current !== null) {
+      clearTimeout(pollTimeoutRef.current);
+      pollTimeoutRef.current = null;
+    }
+  }, []);
+
   const releaseSendGuards = useCallback(() => {
+    clearPollTimeout();
     setSending(false);
     sendingFromAPIRef.current = false;
     sendInFlightRef.current = false;
-  }, []);
+  }, [clearPollTimeout]);
 
   const clearError = useCallback(() => setError(null), []);
 
@@ -146,6 +195,33 @@ export function useChatSend(workspaceId: string, options: UseChatSendOptions) {
             sendInFlightRef.current = false;
             return;
           }
+          // Poll-mode ("queued") turn: the message landed and the
+          // external/MCP agent will pick it up on its next poll, but
+          // there is NO reply in this response. Pre-fix this fell
+          // through to releaseSendGuards() below and the "agent is
+          // working" indicator vanished the instant the POST returned —
+          // an external-workspace turn looked dead even though work had
+          // not started. Instead, keep `sending` true so the existing
+          // thinking indicator (the same one internal agents use)
+          // persists as a "received — agent is working" state; the
+          // terminal AGENT_MESSAGE WebSocket push (consumed by
+          // useChatSocket → onAgentMessage / onSendComplete →
+          // releaseSendGuards) clears it when the real reply arrives,
+          // exactly the path an internal async reply already uses.
+          if (isPollQueuedResponse(resp)) {
+            clearPollTimeout();
+            pollTimeoutRef.current = setTimeout(() => {
+              if (sendTokenRef.current !== myToken) return;
+              if (!sendingFromAPIRef.current) return;
+              releaseSendGuards();
+              setError(
+                "No response yet from this agent — it may be offline or " +
+                  "busy. Your message was delivered and is queued; the " +
+                  "reply will appear here if the agent picks it up.",
+              );
+            }, POLL_QUEUED_REPLY_TIMEOUT_MS);
+            return;
+          }
           const replyText = extractReplyText(resp);
           const replyFiles = extractFilesFromTask(
             (resp?.result ?? {}) as Record<string, unknown>,
@@ -167,9 +243,15 @@ export function useChatSend(workspaceId: string, options: UseChatSendOptions) {
           setError("Failed to send message — agent may be unreachable");
         });
     },
-    [workspaceId, sending, uploading],
+    [workspaceId, sending, uploading, clearPollTimeout],
   );
 
+  // Drop the poll-mode safety timer on unmount / workspace switch so a
+  // stale timeout can't fire setError against a panel the user has
+  // already navigated away from. sendTokenRef guards correctness if it
+  // ever did fire; this just avoids the wasted timer + setState churn.
+  useEffect(() => clearPollTimeout, [clearPollTimeout]);
+
   return {
     sending,
     uploading,