Copy. The mechanism is probably similar once we abandon the "LLM that is asked to generate json" path. But the grammar alone doesn't ensure the output is a probability vector does it?
Both use the softmax operation, but "probability of emitting a given label" is not the same as "probability the decided action is correct". OTOH, taking an action to sample something to come up with "probability of emitting a label" is in fact the whole shebang if the label is the next action. If it works it works.
Who cares, this distinction is small.
For me, a planning guy, either your suggestion or Jev-like would work just fine, and you better believe I'll be testing both as I'm quite excited about being able to use less-structured, untrained systems in decision pipelines. Thanks for the heads up.