A target rendered block by block off one table. The target may read @notes, the sum of
the terms added under handles; an edit to it or to a term plays from the next block on.
One reading off a buffer nothing rendered — an external file, say — under the profile the
caller names. Every representation needing the graph behind it refuses here.
render through store, from the root down: a node the store answers stands as its
samples, and nothing under it is typed, planned or looked up. What the rest computes is
staged beside the store as the render drops it; only persist writes the store.