Function default_space_identity 

pub fn default_space_identity(
    provider: &str,
    model_id: &str,
    dimension: usize,
) -> EmbeddingSpaceIdentity

A non-attested symmetric identity for providers with no registry fixture (hash placeholders, opaque fleet backends, tests).

The artifact hashes are derived from provider/model_id, not from model bytes: this identity states “this vector space is whatever this named provider produces”, which is enough to keep corpora from mixing but is not artifact provenance. Attested paths must supply a complete identity.