ValidationCode:
    | "QTY_INVALID"
    | "QTY_STEP"
    | "QTY_FREEZE_LIMIT"
    | "PRICE_INVALID"
    | "PRICE_OUT_OF_BAND"

Machine-readable rejection code. Three of these (QTY_STEP, QTY_FREEZE_LIMIT, PRICE_OUT_OF_BAND) are spelled exactly as the planned v2 broker contract's RejectCode members, so a mapping to it would be identity; QTY_INVALID and PRICE_INVALID are local, and would fold into its CONTRACT_VIOLATION. Every member is emitted by a branch below: a code nothing can produce would be a label with nothing behind it.