bug#33050: 27.0.50; [macOS] Problem with process input with process-connection-type nil

[Charles A. Roelli]

> From: Thomas Fitzsimmons <fitzsim@fitzsim.org>
> Date: Thu, 25 Oct 2018 21:41:34 -0400
> 
> I re-read the Elisp "Asynchronous Processes" node; when I was deciding
> how to set process-connection-type, I think I was following the
> _underlined_ part in:
>
> [...]
>
>                                         However, _for subprocesses used
>    by Lisp programs for internal purposes, it is often better to use a
>    pipe_, because pipes are more efficient, and because they are immune
>    to stray character injections that ptys introduce for large (around
>    500 byte) messages.

Does anyone recall where these "character injections" come from?  ISTR
that these no longer happen...  Maybe this is a reference to the code
deleted here:

https://git.savannah.gnu.org/cgit/emacs.git/commit/?id=2b0a91e78f83fb446cc38efb99399e83ad2cded3
(as seen, e.g., in Bug#32438)

Also, both "process-send-region" and "process-send-string" (in master)
claim to split their process input if it is longer than 500
/characters/ (not bytes) -- but reading through the code in process.c,
it's not clear where (or if) this still happens.