Tighten disk safety checks

internal/watcher/watcher.go

@@ -135,6 +135,9 @@ func discoverDisks(root string) map[string]disk.DiskInfo {
 			continue
 		}
 		mountPath := filepath.Join(root, entry.Name())
+		if !disk.IsMountPoint(mountPath) {
+			continue
+		}
 		info, _ := disk.Probe(mountPath)
 		if info.State == disk.DiskAbsent {
 			continue
@@ -144,8 +147,10 @@ func discoverDisks(root string) map[string]disk.DiskInfo {
 
 	// If no child mountpoints were detected, the disk may be mounted directly at root.
 	if len(disks) == 0 {
-		if info, _ := disk.Probe(root); info.State != disk.DiskAbsent {
-			disks[root] = info
+		if disk.IsMountPoint(root) {
+			if info, _ := disk.Probe(root); info.State != disk.DiskAbsent {
+				disks[root] = info
+			}
 		}
 	}
 	return disks