Subscribes to one field. Returns null when the field is not active in the
current branch. Inside a , name is the bare member key —
the element path prefixes it, so the same control works at the root and
in any element.
The subscription only fires when the field's snapshot reference changes, and
diffSnapshot preserves that reference for structurally-unchanged fields — so
a full recompute re-renders only the controls whose data actually moved.
Subscribes to one field. Returns null when the field is not active in the current branch. Inside a,
nameis the bare member key — the element path prefixes it, so the same control works at the root and in any element.The subscription only fires when the field's snapshot reference changes, and
diffSnapshotpreserves that reference for structurally-unchanged fields — so a full recompute re-renders only the controls whose data actually moved.