Struct ChainParts 

pub struct ChainParts {
    pub addr: SocketAddr,
    pub mounted: Vec<String>,
    pub metrics: Arc<MetricsRegistry>,
    pub train_worker: Option<EmbeddedWorker>,
}

The non-routing remainder of an AssembledChain after AssembledChain::into_axum_router splits the routes off: the resolved bind address, the mounted-service ledger (for the downstream’s startup log), the engine metrics handle (so a single-listener downstream can re-apply the engine’s MetricsLayer on its own listener), and the training-worker guard the downstream must keep alive for the lifetime of its own serve loop.

Fields

addr: SocketAddr

mounted: Vec<String>

metrics: Arc<MetricsRegistry>

train_worker: Option<EmbeddedWorker>

The embedded training worker guard. The downstream MUST hold this for the lifetime of its serve loop — dropping it stops the worker and submitted jobs stop running.