Function params_of 

pub fn params_of(
    kind: SystemKind,
    surface: ParamSurface,
) -> Vec<&'static ParamSpec>

Every parameter one surface of kind accepts, in the order an author meets them: the system’s own roster first, then the engine stages’.

The membership test this renders is the loader’s, read off the same two rosters is_known_param and compile_bindings consult — so a key the editor underlines is exactly a key the loader would warn about, and a key it accepts is one the loader reads. core/tests/suite/preset_schema.rs validates against this same function, which is what makes the committed JSON and the corpus check one model rather than two.

A name declared by the system and again by a stage appears once, at its first occurrence — the order kind_of_param resolves in.