All my commit messages are a mess and I spend the time that I have designing and writing code, not figuring out how to make the commit message look pretty. That's what merges are for. I don't see the value of this tbh. Just pedantic time wasting.
I have branches that I work in and fork out from in every direction before merging everything back into master. My branches are messy because they're works in progress so I don't care about the commit messages. For the final merge back into master its a high-level overview of changes. I don't try detail every change. I honestly think that devs obsess too much over this clean commit history thing and that it looks to me like pedantic OCD.
I mean, git lends itself to a lot of approaches, the ultimate goal is that the master repo's main branch has a readable and logical set of commit messages usefully describing every change.
Personally I try to avoid merge commits these days, although that's more of a habit than any reasoned position, as such I make frequent use of rebase/squash to edit previous commit messages. Is that worrying about clean commits?