修复: SFTP连接首拉不显示与传输挂起

- watcher握手期伪触发致幻影本地列表，根因修复
- 连接探测2.5s超时竞速，握手10s预算
- 30s保活自动掐死半开连接，取连接时剔除已断开
- 副本命名与进度计数抽公共，下载缓存清理去重

internal/storage/download_cache.go

@@ -4,8 +4,10 @@ import (
 	"crypto/sha256"
 	"fmt"
 	"log/slog"
+	"u-desk/internal/common"
 	"os"
 	"path/filepath"
+	"strings"
 	"time"
 
 	"u-desk/internal/storage/models"
@@ -129,7 +131,7 @@ func DownloadToTempCached(transport, connID, remotePath string, fileSize int64,
 	// 移动文件到确定性路径
 	if err := os.Rename(tempPath, deterministicPath); err != nil {
 		// Rename 可能跨卷失败，尝试 Copy+Delete
-		if copyFile(tempPath, deterministicPath) != nil {
+		if common.CopyFile(tempPath, deterministicPath) != nil {
 			SaveCache(transport, connID, remotePath, fileSize, modTime, tempPath)
 			return tempPath, nil
 		}
@@ -166,23 +168,37 @@ func deterministicCachePath(transport, connID, remotePath string, fileSize int64
 	return filepath.Join(cacheTempDir, fileName), nil
 }
 
-// copyFile 复制文件内容
-func copyFile(src, dst string) error {
-	in, err := os.Open(src)
-	if err != nil {
-		return err
+// CleanupSiteCacheDirs 清理超过 24h 的站点预览缓存目录
+// os.TempDir() 下两个前缀是旧版 MkdirTemp 随机目录残留（sftp 与 oss 各一种）
+func CleanupSiteCacheDirs() {
+	cutoff := time.Now().Add(-downloadCacheTTL)
+	cleaned := cleanupExpiredDirs(cacheTempDir, "site-", cutoff)
+	cleaned += cleanupExpiredDirs(os.TempDir(), "udesk-site-", cutoff)
+	cleaned += cleanupExpiredDirs(os.TempDir(), "udesk-sftp-site-", cutoff)
+	if cleaned > 0 {
+		slog.Info("清理过期站点缓存目录", "count", cleaned)
 	}
-	defer in.Close()
+}
 
-	out, err := os.Create(dst)
+// cleanupExpiredDirs 删除 dir 下修改时间早于 cutoff 的 prefix 前缀子目录，返回清理数量
+func cleanupExpiredDirs(dir, prefix string, cutoff time.Time) int {
+	entries, err := os.ReadDir(dir)
 	if err != nil {
-		return err
+		return 0
 	}
-	defer out.Close()
-
-	if _, err := out.ReadFrom(in); err != nil {
-		os.Remove(dst)
-		return err
+	cleaned := 0
+	for _, e := range entries {
+		if !e.IsDir() || !strings.HasPrefix(e.Name(), prefix) {
+			continue
+		}
+		info, err := e.Info()
+		if err != nil {
+			continue
+		}
+		if info.ModTime().Before(cutoff) {
+			os.RemoveAll(filepath.Join(dir, e.Name()))
+			cleaned++
+		}
 	}
-	return nil
+	return cleaned
 }