except of my dozens or so commits to a feature branch, most of which are "update" or "fix test" or "oops forgot edge case". But for the one squash commit, it's "some-feature-tag: nice description of the changes (#relevant-pr)".

and there's no way I'm going to write more than one nice commit message for a branch.

You can still get the fine-grained commits if you keep your merges focused on one thing.