fix: recover stale WeChat active requests

wechat-mp.mjs

@@ -1012,6 +1012,7 @@ export function isRecoverableWechatAgentSessionError(message) {
   if (/stale_session_poisoned_completion/i.test(normalized)) return true;
   if (/403|404|not found|无权访问/i.test(normalized)) return true;
   if (/tool_calls|tool_call_id|insufficient tool messages/i.test(normalized)) return true;
+  if (/session already has an active request|active request.*cancel/i.test(normalized)) return true;
   if (/wechat_agent_incomplete_reply/i.test(normalized)) return true;
   return false;
 }

wechat-mp.test.mjs

@@ -2714,6 +2714,10 @@ test('isRecoverableWechatAgentSessionError detects poisoned tool_calls history',
   );
   assert.equal(isRecoverableWechatAgentSessionError('stale_session_poisoned_completion'), true);
   assert.equal(isRecoverableWechatAgentSessionError('无权访问该会话'), true);
+  assert.equal(
+    isRecoverableWechatAgentSessionError('Session already has an active request. Cancel it first.'),
+    true,
+  );
   assert.equal(isRecoverableWechatAgentSessionError('network timeout'), false);
 });