One thing that's surprisingly powerful is to just say what you want in the prompt. One of my skill files now includes "inspect existing code under [subdir] for implementation patterns." Depending how much code you have, that might take a lot of tokens. You could either list the patterns that you want or include a smaller code sample in the skill's references.

A stronger version of this would be to make a separate gate. Fail the commit if the new code duplicates something already in a utility function, renames something that already had a name, uses for-loops instead of list comprehensions, whatever is bothering you.