alt-b not working in Mosh

Hi -- hoping someone can help me sort through a key combination issue.

When I use a WSL terminal or a SSH terminal, `alt-b` works correctly in emacs to move the cursor back a word. However, when I enable Mosh in SSH, `alt-b` is broken in emacs, both going back a word and strangely selecting text in the opposite direction.

I tried some troubleshooting, running `cat` then typing `alt-b`. Here's what it printed in various shells:

* wsl: `^[b`
* ssh: `^[b`
* mosh: `^[^@^[b`

Any idea why the extra data is getting appended in mosh for `alt-b`? I tried adding the environment variable:
`MOSH_ESCAPE` with value `1`
But that didn't seem to help.

Also, if I manually invoke mosh (that is, run wsl, and execute mosh from the command line), `alt-b` works properly.

Grateful for any advice!

-Tim

Start by reproducing the issue in FluentTerminal through WSL, SSH, and Mosh, then compare the `cat` output for `alt-b` with the sequences reported in the issue. Done means `alt-b` produces the expected input in Mosh and moves backward by a word in Emacs without selecting text.

Written by the indexing model from the issue text.