fix(h5-chat): queue main-session submits while agent is busy

Prevent silent drops when users send follow-up instructions during waiting or streaming by showing the message immediately, notifying them it is queued, and auto-flushing after the composer returns to idle.

Co-authored-by: Cursor <cursoragent@cursor.com>

chat-agent-run-gate.test.mjs

@@ -1,6 +1,9 @@
 import assert from 'node:assert/strict';
 import test from 'node:test';
 import {
+  buildQueuedChatSubmitNotice,
+  canFlushQueuedChatSubmit,
+  isChatSubmitBusy,
   reconcileSessionEventRequestContext,
   resolvePostAgentRunChatState,
   shouldIgnoreZeroActivityFinish,
@@ -145,6 +148,52 @@ test('missing ActiveRequests cannot unlock while the Portal agent-run is pending
   );
 });
 
+test('isChatSubmitBusy covers active composer states', () => {
+  assert.equal(isChatSubmitBusy('idle'), false);
+  assert.equal(isChatSubmitBusy('error'), false);
+  assert.equal(isChatSubmitBusy('waiting'), true);
+  assert.equal(isChatSubmitBusy('streaming'), true);
+  assert.equal(isChatSubmitBusy('connecting'), true);
+});
+
+test('buildQueuedChatSubmitNotice reflects queue depth', () => {
+  assert.match(buildQueuedChatSubmitNotice(1), /当前任务完成后/);
+  assert.match(buildQueuedChatSubmitNotice(2), /2 条待执行/);
+});
+
+test('canFlushQueuedChatSubmit waits for idle composer without pending tool or run', () => {
+  assert.equal(
+    canFlushQueuedChatSubmit({
+      chatState: 'idle',
+      queueLength: 1,
+    }),
+    true,
+  );
+  assert.equal(
+    canFlushQueuedChatSubmit({
+      chatState: 'waiting',
+      queueLength: 1,
+    }),
+    false,
+  );
+  assert.equal(
+    canFlushQueuedChatSubmit({
+      chatState: 'idle',
+      agentRunPending: true,
+      queueLength: 1,
+    }),
+    false,
+  );
+  assert.equal(
+    canFlushQueuedChatSubmit({
+      chatState: 'idle',
+      pendingTool: true,
+      queueLength: 1,
+    }),
+    false,
+  );
+});
+
 test('reconcileSessionEventRequestContext adopts Goose request id while agent-run gate waits', () => {
   assert.deepEqual(
     reconcileSessionEventRequestContext({