Whether the document has changed since its newest marker - the store's own comparison, not something a client derives.
A property of the document, so it is on the page rather than on each entry: "changed since the newest marker" is one question however many rows the page carries.
`Option`, not `bool`, and that is the whole compatibility story. A bare bool with #[serde(default)] reads false - not stale - from every store built before this field existed, and a client that believed it would offer to rename a marker over a document that has moved on. None means this store does not say, and a caller must then fall back to whatever it did before it could ask.
Some(true) when the document has no markers at all: there is nothing to be unchanged relative to.
