Feature request: support eternal terminal

Mosh has some native drawbacks, for example we can’t use the scrollback or remix control mode
But eternal terminal doesn’t have these problems. So can we consider add the et command support?

Start by reviewing how Blink currently invokes and integrates Mosh and how terminal scrollback and control mode are handled. Determine the scope of adding the `et` command support, then verify that an Eternal Terminal session preserves the requested terminal behavior without regressing existing Mosh support.

Written by the indexing model from the issue text.