修复 Windows 后端退出：taskkill 结束进程树 + turn.completed 支持 (#108)

* fix(executor): handle turn.completed and terminate process tree on Windows

* fix: 修复代码审查发现的安全和资源泄漏问题

修复内容：
1. Windows 测试 taskkill 副作用：fake process 在 Windows 上返回 Pid()==0，避免真实执行 taskkill
2. taskkill PATH 劫持风险：使用 SystemRoot 环境变量构建绝对路径
3. stdinPipe 资源泄漏：在 StdoutPipe() 和 Start() 失败路径关闭 stdinPipe
4. stderr drain 并发语义：移除 500ms 超时，确保 drain 完成后再访问共享缓冲

测试验证：
- go test ./... -race 通过
- TestRunCodexTask_ForcesStopAfterTurnCompleted 通过
- TestExecutorSignalAndTermination 通过

Generated with SWE-Agent.ai

Co-Authored-By: SWE-Agent.ai <noreply@swe-agent.ai>

---------

Co-authored-by: cexll <evanxian9@gmail.com>
Co-authored-by: SWE-Agent.ai <noreply@swe-agent.ai>

codeagent-wrapper/parser.go

@@ -163,6 +163,10 @@ func parseJSONStreamInternal(r io.Reader, warnFn func(string), infoFn func(strin
 				isCodex = true
 			}
 		}
+		// Codex-specific event types without thread_id or item
+		if !isCodex && (event.Type == "turn.started" || event.Type == "turn.completed") {
+			isCodex = true
+		}
 		isClaude := event.Subtype != "" || event.Result != ""
 		if !isClaude && event.Type == "result" && event.SessionID != "" && event.Status == "" {
 			isClaude = true
@@ -194,6 +198,10 @@ func parseJSONStreamInternal(r io.Reader, warnFn func(string), infoFn func(strin
 				infoFn(fmt.Sprintf("thread.completed event thread_id=%s", event.ThreadID))
 				notifyComplete()
 
+			case "turn.completed":
+				infoFn("turn.completed event")
+				notifyComplete()
+
 			case "item.completed":
 				var itemType string
 				if len(event.Item) > 0 {