feat: 预算警告 & Shadowing 防护 & 记忆容量管理 (v5.1.2)

- 预算警告临时层：Agent Loop 剩余 ≤5 轮注入 WARNING，≤2 轮注入 CRITICAL
- MCP Shadowing 防护：MCP 工具注册时检测重名，自动跳过并警告
- 记忆容量限制：上限 500 条，超限自动清理低价值条目（rule 受保护）
- 版本号更新至 5.1.2

src/renderer/services/agent-engine.ts

@@ -529,6 +529,17 @@ export async function runAgentLoop(
     const toolCalls: ToolCall[] = [];
     allCallsThisLoop = [];
 
+    // v5.1.2 预算警告：接近迭代上限时注入临时提示
+    let budgetWarningIdx = -1;
+    const remaining = maxLoops - loopCount + 1;
+    if (remaining <= 5 && remaining > 0) {
+      const warning = remaining <= 2
+        ? `\n⚠️ CRITICAL: You have only ${remaining} iteration(s) left. Stop using tools and provide your final answer NOW.`
+        : `\n⚠️ WARNING: You have approximately ${remaining} iterations remaining. Start wrapping up and prepare your final answer.`;
+      messages.push({ role: 'system', content: warning });
+      budgetWarningIdx = messages.length - 1;
+    }
+
     const abortController = new AbortController();
     state.set(KEYS.ABORT_CONTROLLER, abortController);
 
@@ -587,6 +598,10 @@ export async function runAgentLoop(
         return;
       }
       logError('流式调用异常', (err as Error).message);
+      // 清理预算警告临时消息
+      if (budgetWarningIdx >= 0) {
+        messages.splice(budgetWarningIdx, 1);
+      }
       if (content || thinking) {
         messages.push({ role: 'assistant', content: content || '（模型响应异常）', ...(thinking && { thinking }) });
       }
@@ -594,6 +609,11 @@ export async function runAgentLoop(
       return;
     }
 
+    // 清理预算警告临时消息
+    if (budgetWarningIdx >= 0) {
+      messages.splice(budgetWarningIdx, 1);
+    }
+
     // 提取 ReAct 思考过程
     const thoughtMatch = content.match(/\*\*Thought:\*\*\s*([\s\S]*?)(?=\*\*Action:\*\*|\*\*Final Answer:\*\*|$)/i);
     const thought = thoughtMatch ? thoughtMatch[1].trim() : '';