feat(engine): introduce agent handoff tracing and data integrity validation based on Astra analysis

src/lib/engine.ts

@@ -2,6 +2,7 @@ import * as vscode from 'vscode';
 import { lockManager } from '../core/lock';
 import { actionQueue } from '../core/queue';
 import { logInfo, logError } from '../utils';
+import { AgentDataValidator, PerformanceProfiler } from './diagnostics';
 
 // ─────────────────────────────────────────────
 // 1. 에이전트 인터페이스 확장 (Interface Extensibility)
@@ -451,7 +452,13 @@ export class AgentEngine {
                     this.checkAbort(signal);
                 }
 
-                return await agent.execute(input, context, signal, options);
+                const startTime = Date.now();
+                const result = await agent.execute(input, context, signal, options);
+                const durationMs = Date.now() - startTime;
+                
+                PerformanceProfiler.logLLMLatency(agentName, durationMs, result.length);
+                
+                return result;
             } catch (error: any) {
                 lastError = error;
                 const { type, rule } = ErrorClassifier.classify(error);
@@ -536,8 +543,7 @@ export class AgentEngine {
     }
 
     private validateResult(data: string, step: string) {
-        if (!data || data.trim().length < 10) {
-            throw new Error(`${step} 에이전트로부터 유효한 응답을 받지 못했습니다.`);
-        }
+        // Error Recovery Matrix: Permanent 오류 발생을 방지하기 위한 선제적 핸드오프 검증
+        AgentDataValidator.validateHandoff(step, data);
     }
 }