alt-b not working in Mosh

[timnevits]

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