Allow string interpolation in prompts for custom modes

[pehrlich-arbor]

Hello!

I'm looking to write a custom mode to speedily open pull requests.

Current behavior:

When asked to open a PR, Roo will run a number of commands to learn the git setup -- git status, git log --oneline -10 git branch -r, git remote -v, and so on. This will help it know whether changes have been committed, where to open the PR, the base branch, and so on.

Feature Request

When writing my prompt, I'd love to run those commands once (perhaps when switching into the Custom Mode) and send along the outputs in the initial contest. This would greatly reduce the number of round-trips involved in opening a pull request.

Seems related to, but different from #4183

[adamjen]

Did you try asking roo code to make a custom mode to do these exact steps?