feat: add resumable file archive jobs and offline verification

internal/retention/job_lock_unix.go

@@ -0,0 +1,27 @@
+//go:build linux || darwin
+
+package retention
+
+import (
+	"errors"
+	"os"
+	"syscall"
+)
+
+// lockJob 的非阻塞文件锁随进程退出自动释放，不使用永不过期的“锁目录”。
+func lockJob(root *os.Root) (*os.File, error) {
+	f, err := root.OpenFile(".lock", os.O_CREATE|os.O_RDWR|syscall.O_NOFOLLOW, 0600)
+	if err != nil {
+		return nil, err
+	}
+	info, err := f.Stat()
+	if err != nil || !info.Mode().IsRegular() || info.Mode().Perm()&0077 != 0 {
+		f.Close()
+		return nil, errors.New("invalid archive lock file")
+	}
+	if err := syscall.Flock(int(f.Fd()), syscall.LOCK_EX|syscall.LOCK_NB); err != nil {
+		f.Close()
+		return nil, errors.New("archive job is locked or filesystem does not support locking")
+	}
+	return f, nil
+}