Return a stream to write to.

Prefetch as many recipes as we need to get back to an optimal snapshot.

Given a set of paths in one snapshot, rebase them into a snapshot further down the edit stream.

Find recipes, traversing backwards from `want` to `have`, but only looking at recipes tagged with the given pointer.

Get all the recipes needed, traversing backwards from `want` to `have`.

Get a tree of the recipes needed, with `want` at the root and `have` in a leaf node.

A tree structure for accumulating recipes.

A simple interface for storing large files.