This is done in the command, rather than in the op,
- To consistently construct the `Workspace`
- It is more composable as an API
A downside is we update the git dependencies a second time.
We are not rolling back on error.
- For some errors, the user might want to debug what went wrong
- Rollback adds its own complications and risks, including since its
non-atomic
Fixes#10901
In writing the contrib documentation for functional vs ui tests, I
realized that as we work to make snapbox work for the functional tests,
we'll need distinct `Assert` objects since we'll want to elide a lot
more content in functional tests. I'm making room for this by
qualifying the existing asserts as being for "ui".
