KM> I wonder if the whole idea of a "primary" shell in the
environments is
 KM> moot. 

No it isn't.  The "primary" command processor is the first
command processor to run in any given session/console/login session, and on
OS/2 Warp, linux, UNIX, and other operating systems this distinction is
still important.  On OS/2 Warp, for example, the primary command processor
in each session creates the per-session shared memory objects that are used
to share history, aliases, directory history, and so forth.  On UNIX,
handling of SIGHUP, and dealing with other events that affect the session
as a whole, is the responsibility of the "primary command
processor" (UNIX calls it the "login shell").

 KM> There's probably not another one, a "primary", parts of which get 
 KM> used, underneath that. So each processor you start _is_ a 
 KM> "primary" processor, [...]

No.  "primary" means no more than "first".  It doesn't
necessarily imply that all of the crazy shenanighans that happen with 4DOS
in DOS will happen.  It merely implies that the command processor is the
first one to run in the given session.

 ¯ JdeBP ®

--- FleetStreet 1.19 NR