feat: 实现发送消息前余额检测

- creditsService.ts: 新增余额缓存和检测服务
- apiClient.ts: 新增 getCreditBalance() API 调用
- dialogService.ts: SSE credit_update 事件更新余额缓存
- messageHandler.ts: 发送消息前检测余额，低于5点阻止发送

src/utils/messageHandler.ts

@@ -18,6 +18,7 @@ import { ChatHistoryManager } from "./chatHistoryManager";
 import { dialogManager, DialogSession } from "../services/dialogService";
 import { userInteractionManager } from "../services/userInteraction";
 import { healthCheck } from "../services/apiClient";
+import { checkBalanceBeforeSend } from "../services/creditsService";
 
 import type { RunMode, ServiceTier } from "../types/api";
 
@@ -90,6 +91,27 @@ export async function handleUserMessage(
     return;
   }
 
+  // 发送前检测余额
+  const balanceCheck = await checkBalanceBeforeSend();
+  if (!balanceCheck.allowed) {
+    console.warn("[MessageHandler] 余额不足，阻止发送:", balanceCheck.message);
+    // 显示错误提示
+    const selection = await vscode.window.showWarningMessage(
+      balanceCheck.message || "资源点余额不足",
+      "去充值"
+    );
+    if (selection === "去充值") {
+      vscode.env.openExternal(vscode.Uri.parse("https://iccoder.com/recharge"));
+    }
+    // 恢复输入状态
+    panel.webview.postMessage({
+      command: "updateSegments",
+      segments: [],
+      isComplete: true,
+    });
+    return;
+  }
+
   // 尝试使用后端服务
   if (useBackendService && extensionPath) {
     try {