Function deploy_by_digest 

pub async fn deploy_by_digest(
    registry: &dyn ReleaseRegistry,
    ledger: &dyn RunLedger,
    agent_name: &str,
    timestamp: Option<DateTime<Utc>>,
) -> Result<DeployResult>

Deploy an agent by looking up its current release digest.

Resolves the agent’s current release via the registry, then delegates to DeployByDigestRunner to create a deterministic run. Finally replays the run to produce a ReplaySummary suitable for golden equality testing.

Pass a fixed timestamp to get deterministic digests across invocations.