Retrieve runtime fact requirements per Action type. For each Action, shows which input facts must be present in the execution payload — e.g. MUTATE_FACT always requires its targetVar fact, plus refVar when one is specified. The factRequired flag describes the FACT, not the parameter: refVar is an optional parameter, but if you specify it the named fact must exist. A required fact absent at runtime throws — the engine never defaults to 0. These facts must be sent in the request (P-015 otherwise), even when an earlier action in the same rule writes them. SET_FACT requires no input fact: it is the only action whose targetVar the request does not have to send, and that targetVar must be a registered fact (ACT-032). Static data, safe to cache in-session.