Yichen Jiang
8a3c5daad7
A form needs two things the snapshot did not carry. The `user` layer tells it which fields the user overrode — presence, not value equality, because an override equal to the composition default is still an override — and `base` is what a cleared field reverts to. `unset` is that clear, sharing `set`'s queue, revision fence, and rejected-write recovery through one write path.