Constant ONNX_IR_VERSION_MAX 

pub const ONNX_IR_VERSION_MAX: i64 = 13;

The highest ONNX IR version this realization admits — onnx.proto’s current Version::IR_VERSION (= 13, 2026). The realization accepts any ir_version in 1..=ONNX_IR_VERSION_MAX: the canonical skeleton is IR-version-agnostic (the field numbers it reads are stable across IR revisions; IR-v10+ NodeProto.overload simply reads empty on older models), and the ir_version value itself is bound into the skeleton, so two IR revisions of the same logical model canonicalize distinctly. Admitting the range lets the realization content-address real-world models (published exports are predominantly IR 6–10) rather than only the latest revision.