The challenge envelope returned by getmatmulservicechallenge. Opaque to the SDK at the wire boundary — pass through to solver / redeem.
Open extension.
Optional
btxd schema kind discriminator (e.g. "matmul_service_challenge_v1").
The challenge envelope returned by getmatmulservicechallenge. Opaque to the SDK at the wire boundary — pass through to solver / redeem.