Variable REJECTION_SPEC`Const`

REJECTION_SPEC: {
    readonly [K in RejectionCode]: {
        fields: readonly Exclude<
            keyof Extract<RejectionDetail, { reason: K }>,
            "reason",
        >[];
    }
} = ...

Per-code registry of the fields each rejection's detail carries. The mapped key set and the keyof-derived field lists are both compile-locked to RejectionDetail, so this catalog cannot drift from the union.