A2uiFunctionException

Thrown when a FunctionCall cannot be evaluated.

This is about the call, not about the data it reads: a missing argument, an argument of the wrong type, a function no catalog defines, @index outside a list template, an evaluation that outgrows its budget. A binding that resolves to nothing is not one of these — the specification requires a renderer to tolerate that and show a placeholder, so it produces JsonNull instead.

It is a RuntimeException rather than a dev.ynagai.a2ui.core.protocol.A2uiFormatException for the same reason dev.ynagai.a2ui.core.surface.A2uiStateException is: the payload parsed. Note that neither of those is a supertype of this one, so a renderer evaluating agent-sent expressions has to catch all three — JsonPointer.parse still raises the format one for a malformed path.