Implement chat queue fallback

ai_knowledge_base_v2/apps/user-client/src/App.vue

@@ -84,12 +84,30 @@ async function send(message: string) {
   messages.value.push(userMessage, assistantMessage);
   loading.value = true;
   activeAbortController.value = new AbortController();
+  let hasContent = false;
   await scrollToBottom();
   try {
-    await streamChat(activeSessionId.value, message, async (chunk) => {
-      assistantMessage.content += chunk;
-      await scrollToBottom();
-    }, activeAbortController.value.signal);
+    await streamChat(
+      activeSessionId.value,
+      message,
+      async (chunk) => {
+        if (!hasContent) {
+          assistantMessage.content = "";
+          hasContent = true;
+        }
+        assistantMessage.content += chunk;
+        await scrollToBottom();
+      },
+      async (statusMessage, statusType) => {
+        if (statusType === "queued") {
+          assistantMessage.content = statusMessage || "当前请求较多，正在排队中。";
+        } else if (statusType === "generating" && !hasContent) {
+          assistantMessage.content = "";
+        }
+        await scrollToBottom();
+      },
+      activeAbortController.value.signal,
+    );
     assistantMessage.streaming = false;
     await refreshSessions(activeSessionId.value);
     user.value = await api.profile();