Class PlanBuilder<From>

Adds a node under a caller-chosen slot name.

The name is required rather than derived, because it is the stable identity — deriving sma2 from a counter would renumber the moment a node is inserted above it, which is the property slots exist to provide.

Names the result, so a later request can refer back to it.

Surfaces a node under the caller's own name.

Takes a handle, because a selector's only remaining job is to point at a node — what comes back is whatever that node produces.

The envelope. Plain JSON — nothing here survives into the request.