Automatic snapshot on nested `agentfs run`

[penberg]

@divyenduz had this idea of doing automatic snapshot on nested agentfs run, which seems like a really nice way of branching off coding agents.

Depends on #57

[kriyanshii]

Hey I would love to take this on

[eureka928]

Hi @penberg @avinassh nice to meet you

I'd like to contribute on this project.
May I take this as a first contribution?

Thank you for your time