VERSION
VERSION = 1
Format marker, so a future change is a new version rather than a silent misread.
A complete index of what the site held at one instant, or the change since the last one.
The thing a replay starts from. Without an anchor, materializing a subject means walking every segment back to the root of history, which is fine on a site a week old and unusable on one a year old.
A manifest is a flat list of subjects, not a tree, and the reason is measured. A Merkle tree over the same index rewrites an interior node to record one changed leaf, which at any fanout costs roughly sixteen to twenty times the entry it is recording; the earlier subtree implementation wrote 3,989,289 bytes to record a 201-byte change across 50,000 subjects. A flat list of the subjects that changed since the previous manifest costs the entries themselves and nothing else, and it chains, so an anchor every four hours costs about 240 bytes per changed subject.
Two kinds. A full manifest lists every subject and ends the chain. A delta manifest lists what changed since its parent, and a NULL entry is a subject that was deleted - which has to be recorded explicitly, because a delta that simply omitted it would leave the parent's entry standing and resurrect it.
Content-addressed like everything else, so writing the same manifest twice writes one object.