provide unopened FCBs to launched applications
May I ask why do we (you) want this? What is it for?
this is an arcane compatibility item. When executing a program, DOS (COMMAND.COM) parses the command line and prepares two unopened FCB records in the application's PSP with the filenames mentioned respectively in first and second argument, so the application can use them right away instead of having to perform command line lookups and preparing FCB entries. This is presumably used by some old (DOS 1.x era) programs.
here's a simple test program I devised today (toys/fcbdir.asm):
(from SVARCOM TODO LIST todo.txt)