Function resolve 

pub fn resolve(conflict: &Conflict, choice: Resolution) -> BufferEntry

Picks one of conflict’s versions (Ours/Theirs, both by explicit source name — there is no “current vs incoming” side at this generic level, that distinction belongs to whatever UI drives this, see the TODO below) or builds a fresh Put from Custom. Panics if the named source is not one of conflict’s versions — the caller is expected to only offer resolutions built from conflict.versions in the first place.