MessageProcessor

Folds agent-to-renderer messages into RendererState.

This is the incremental half of the protocol: a surface is built up by a stream of messages that each carry only what changed, and convergence depends on applying them in order. The order MUSTs are enforced here — a surface cannot be created twice, and cannot be updated or deleted before it is created — and raise A2uiStateException.

Everything that needs a catalog is out of scope. A component whose properties the catalog does not define, a child reference that names nothing, a function call with the wrong argument types: all of those are accepted into state here and rejected by the validator, which is also what lets progressive rendering work at all.