I've tried to add an integration test of sorts, but the "No live threads left" error got the better of me.

@andrehjr Check this out.

Hi @dgutov I've made some additional changes on your PR. Can you try it?

Investigating a bit more, it seems this issue only happens when Reline is used in Pry as input (Ruby 3.3+). When I've tried emacs on the shell with older versions of ruby there was no issue.

I think this code might be removed if ruby/reline#660 changes how Reline treats TERM=dumb, but for now, it solves the echoing issue.

@andrehjr This works for me, thank you. This particular issue indeed seems Reline-specific (there were other bugs before, also related to Reline, but in the context of Pry IIUC they were triggered only with Rubies compiled without libreadline, so those should be covered as well).

Thanks for the link, I guess ruby/irb#907 also helped with that.

Speaking of the difference in solution, I think switching to SimpleStdio whenever the terminal is dumb and the user didn't choose any other input explicitly, makes a bit more sense conceptually, since it also covers unknown unknowns. But I don't mind the difference that much, and maybe we'll have a working Reline inside Emacs not too far off in the future.

@andrehjr Ping.

Ping on this thx!