A keyed collection in the render algebra — structurally identical to
Phoenix.LiveView.Comprehension. AshUi always emits keyed entries
(has_key?: true) and never emits streams: collections are keyed
comprehensions over resource state by model, permanently — stream and
LiveComponents are excluded from this algebra by design, not omission.
Entries are {key, vars, render_fun} where render_fun.(changed_vars, track_changes?) returns the entry's dynamic list.