The LLM driver's capabilities: the stub stands in for a model answer, so it accepts what the LLM driver does.
Runs the two context hooks (the driver contract), logs the input, and answers from the table.
Checks each output's constraint type, target mode, and rules against Capabilities. An output with no constraint is not checked for its constraint type unless the type requires constraints.
OptionalfieldValues: FeaturePipelineFieldValueLookupOne message per output or rule this driver cannot satisfy; empty when it can produce them all.
The driver: reads the input field from the prompt data the processor built and answers from the table.