E-PE0009 — Invalid axis expression

Error Type	Protobuf Error
Phase	loading a model via protobuf (`from_protobuf`)
Python exception	`jijmodeling.ProtobufError`

Message

Invalid axis expression: expected a literal natural number, but got `{actual}`

Cause

The serialized model stores tensor-fold axes through the deprecated axis_ids field, and one of the referenced expressions is not a literal natural number. Current JijModeling releases always write axes as plain integers via the axes field and only accept integer axes, so this error only occurs for bytes produced by an older release or by external tooling.

Fix

Re-export the model with a current JijModeling release, which writes axes as plain integers. If the bytes are produced by external tooling, use the axes field, or make every expression referenced by the deprecated axis_ids field a literal non-negative integer.