Function upsert_agent 

pub async fn upsert_agent(
    persistence: &dyn PersistenceLayer,
    agent: &AgentArtifact,
) -> Result<()>

Upsert an agent artifact as-is (used by the embedded admin surface).

Unlike create_agent this preserves the caller-provided id and kind, so a host can round-trip an artifact it already owns without mutation.

Errors

Returns an error if the persistence write fails.