I can't just get the answer and builder out of Put in a single call.

There is no way to get out `Put a -> (a, Builder)` in a single call.

This is also a wart in the design of `cereal`.

This seems to be a bit of a lacuna in the current design.

Start by reading the current Put API and how its Builder result is exposed, then compare the corresponding cereal design mentioned in the issue. Define what a single-call API should return and how completion would be demonstrated; the issue does not name files or tests, so locating the relevant implementation and test coverage is part of the initial research.

Written by the indexing model from the issue text.