bin/60379: file(1) should recognize snapshot files

>Number:         60379
>Category:       bin
>Synopsis:       file(1) should recognize snapshot files
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Jun 28 18:20:00 +0000 2026
>Originator:     Taylor R Campbell
>Release:        current, 11, 10, 9, ...
>Organization:
The NetBSnapD Filer, Inc.
>Environment:
>Description:

	file(1) should recognize snapshot files as such, rather than
	report `regular file, no read permission'.

>How-To-Repeat:

	# fssconfig fss0 / /.snap/20260628T181411Z
	# ls -loa /.snap
	total 8720
	drwxr-xr-x   2 root  wheel  -            512 Jun 28 18:14 .
	drwxr-xr-x  23 root  wheel  -            512 Jun 28 18:13 ..
	-rw-------   1 root  wheel  snap 63763907072 Jun 28 18:14 20260628T181411Z
	# file /.snap/20260628T181411Z
	/.snap/20260628T181411Z: regular file, no read permission

>Fix:

	Yes, please!  Presumably it is just a matter of checking
	st_flags for SF_SNAPSHOT like ls(1) does, via
	flags_to_string(3) in libutil:

    596 					flags =
    597 					    flags_to_string((u_long)sp->st_flags, "-");

https://nxr.netbsd.org/xref/src/bin/ls/ls.c?r=1.79#595

     68 char *
     69 flags_to_string(u_long flags, const char *def)
     70 {
...
     92 	if (flags & SF_SNAPSHOT)
     93 		SAPPEND("snap");

https://nxr.netbsd.org/xref/src/lib/libutil/stat_flags.c?r=1.3#63