lib/INS@d2fRCK ?

Fingprinting a staging jail with 14.2 shows a half-dozen new files that
didn't exist in 14.1 but one in particular, without a man page, that is
unlike the rest:

   # file lib/INS@d2fRCK
   (ELF 64-bit LSB shared object, x86-64, version 1 (FreeBSD), dynamically linked, for FreeBSD 14.2, stripped)

Checksums indicates it is a copy of libmt.so.5:

   # md5sum lib/*
   4987e6ba61e36eeff23de3acaa4ee771  lib/INS@d2fRCK
   4987e6ba61e36eeff23de3acaa4ee771  lib/libmt.so.5

Questions are:

   a) is it safe to delete,
   b) what buildworld delete-old{,-libs} or etcupdate function might have created it,
   c) should I be checking for other apparent tempfiles, and
   d) if so, how?

Roger Marquis