Static REGISTRY 

static REGISTRY: &[((&str, &str), fn() -> CurveRecipe)]

The registered default recipes, keyed by (cashflow_ccy, collateral_ccy), each single-sourced: a richer recipe in its own file, a par-OIS-only one as a row of ois::OIS_ONLY. (X, X) is a currency’s own recipe; (X, Y) (X ≠ Y) is a cross-collateral recipe. This is the immutable base: never mutated at runtime, and a recipe added here appears to callers without restating.