Avoid pruning some commits within a repo

[Ryan Rueth <rrueth gmail com>]

Hello,

We have a build repo that contains branches for multiple components of our build. This lets us skip rebuilding components that already exist in the build repo, but the various components are re-built at different frequencies. I'd like to prune old objects from this directory, but avoid deleting a component that is still being used for the whole build.

Does anyone have any recommendations for how I might prune a repository, but avoid pruning some old commits that are currently the HEADs of branches and still in use?

My current plan was to use the following to prune commits:

ostree --repo=<repo> prune --keep-younger-than='7 days ago' --refs-only

As an example, if I could do something like `touch` a commit that is the HEAD of a given branch to update the timestamp, then I could just `touch` all of the commits that are used for the full build each time. Thus, when the prune command ran, the still-in-use commits would be more recent than 7 days old.

Thanks,

Ryan