One that:

1. creates a temp directory;
2. checks out the given commit;
3. git-annex gets the data files;
4. runs bids-validator;
5. runs the output through ansifilter --html --fragment --line-numbers --anchors=self
6. spits out a minimal HTML header and footer for the fragment
7. cleans up the temp directory

See the current worker script for a skeleton.