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

[Undiscussed Horrific Abuse, One Victim of Many]

i guess it would be good to retain is_full() in parallel with height
<= max_depth since the concept is partial . these are just metrics
that can be applied to portions of the graph, in order to judge what
to collect where. the metrics are basically the same.