feat(focil): payload envelope event trigger for IL service

Add a payload envelope monitor that subscribes to the
ExecutionPayloadAvailable SSE event (following the existing
beacon_head_monitor pattern). The inclusion list service now races
the IL deadline (66.67% into slot) against the payload envelope
event, matching Lodestar's Promise.race approach.

This ensures IL production fires as soon as the envelope is imported
(when the EL has fresh state) rather than at a fixed offset that may
be too early or too late.

validator_client/src/lib.rs

@@ -14,7 +14,7 @@ use tokio::sync::Mutex;
 use account_utils::validator_definitions::ValidatorDefinitions;
 use beacon_node_fallback::{
     BeaconNodeFallback, CandidateBeaconNode, beacon_head_monitor::HeadEvent,
-    start_fallback_updater_service,
+    payload_envelope_monitor::PayloadEnvelopeEvent, start_fallback_updater_service,
 };
 use clap::ArgMatches;
 use doppelganger_service::DoppelgangerService;
@@ -418,6 +418,13 @@ impl<E: EthSpec> ProductionValidatorClient<E> {
             None
         };
 
+        // Create the payload envelope monitor channel for the inclusion list service.
+        // This allows the IL service to fire early when a payload envelope is available.
+        let (payload_envelope_tx, payload_envelope_rx) =
+            mpsc::channel::<PayloadEnvelopeEvent>(MAX_HEAD_EVENT_QUEUE_LEN);
+        beacon_nodes.set_payload_envelope_send(Arc::new(payload_envelope_tx));
+        let payload_envelope_rx = Some(Mutex::new(payload_envelope_rx));
+
         let beacon_nodes = Arc::new(beacon_nodes);
         start_fallback_updater_service::<_, E>(context.executor.clone(), beacon_nodes.clone())?;
 
@@ -564,6 +571,7 @@ impl<E: EthSpec> ProductionValidatorClient<E> {
             .beacon_nodes(beacon_nodes.clone())
             .executor(context.executor.clone())
             .chain_spec(context.eth2_config.spec.clone())
+            .payload_envelope_rx(payload_envelope_rx)
             // TODO(focil) make config driven
             .disable(false)
             .build()?;