On 2/7/2023 10:20 AM, miha--- via Bug reports for GNU Emacs, the Swiss 
army knife of text editors wrote:
> You might also be interested in how comint deals with this. It can
> handle the case when the user yanks something in the middle of output as
> well. See function comint--mark-as-output, bug#3735 and bug#18135 for
> more details.

Good call. Here's a patch that (mostly) copies those comint functions 
over to Eshell.