SemanticsScope

Semantics collector for one retained node.

The scope is owned by the SemanticsNode.semantics callback and is valid only until that callback returns. Every access must use the tree's owner thread. Access after the callback or from another thread fails. Emitted values are retained as the complete local payload in emission order. Text remains unresolved until a platform adapter consumes the resulting entries. The tree is poisoned once pipeline work has started only when a scope access exception escapes the owning semantics callback.