[spam][crazy][ot] log: #3 write-anywhere to an append-only-log

[Undiscussed Horrific Abuse, One Victim of Many]

so basically an important property is not whether the tree is full or
not, it is rather
- whether it is refrained from exceeding the max depth
- where parts of it are pulled out in order to produce that limit

the parts of it that are pulled out should go near future writes, so
as to combine with them and make a balanced tree

depth > fullness