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.mjs

@@ -72,6 +72,49 @@ export function shouldScheduleMissingActiveRequestGrace({
   return allowMissingGrace && !agentRunPending;
 }
 
+export const QUEUED_CHAT_SUBMIT_NOTICE =
+  '已收到你的消息，将在当前任务完成后自动继续执行。';
+
+/**
+ * @param {string | undefined | null} chatState
+ * @returns {boolean}
+ */
+export function isChatSubmitBusy(chatState) {
+  return (
+    chatState === 'streaming' ||
+    chatState === 'loading' ||
+    chatState === 'connecting' ||
+    chatState === 'waiting'
+  );
+}
+
+/**
+ * @param {number | undefined | null} queueLength
+ * @returns {string}
+ */
+export function buildQueuedChatSubmitNotice(queueLength = 1) {
+  const length = Math.max(1, Number(queueLength) || 1);
+  if (length <= 1) return QUEUED_CHAT_SUBMIT_NOTICE;
+  return `已收到你的消息，当前还有 ${length} 条待执行，将在任务完成后按顺序继续。`;
+}
+
+/**
+ * @param {{ chatState?: string; agentRunPending?: boolean; pendingTool?: boolean; queueLength?: number }} input
+ * @returns {boolean}
+ */
+export function canFlushQueuedChatSubmit({
+  chatState = 'idle',
+  agentRunPending = false,
+  pendingTool = false,
+  queueLength = 0,
+} = {}) {
+  if (!queueLength || queueLength <= 0) return false;
+  if (isChatSubmitBusy(chatState)) return false;
+  if (agentRunPending) return false;
+  if (pendingTool) return false;
+  return true;
+}
+
 /**
  * Only transport uncertainty may continue a run after submit fails. A
  * deterministic gateway error already has a terminal outcome and must return