I feel like that requires a lot of coordination that I, in the midst of development, don't necessarily have. Taking my WIP and trying to build a story around it at each step requires a lot of additional effort, but I can see how that would be useful for the reviewer.

We can agree that we don't need those additional steps once the PR is merged, though, right?

I have literally never met a developer who does this (including myself). 99% of all PRs I have ever created or reviewed consist of a single commit that "does the thing" and N commits that fix issues with/debug failure modes of the initial commit.

Yeah, make it work. Commit. Build unit test. Commit. Fix bugs. Commit. Make pretty. Commit and raise a PR.

You never design a solution which needs multiple architectural components which _support_ the feature? I do, and would make little sense to merge them as separate PRs most of the time as that would mean sometimes tests written on the inappropriate level, also a lot more coordination and needs a lot more elaborate description then just explain how the set of components work in tandem to provide the user value.