feat: add a method to get payload resolve future

crates/payload/builder/src/service.rs

@@ -158,6 +158,17 @@ impl<T: PayloadTypes> PayloadBuilderHandle<T> {
         }
     }
 
+    /// Same as [`Self::resolve_kind`] but returns the underlying future.
+    pub async fn resolve_kind_fut(
+        &self,
+        id: PayloadId,
+        kind: PayloadKind,
+    ) -> Result<Option<PayloadFuture<T::BuiltPayload>>, PayloadBuilderError> {
+        let (tx, rx) = oneshot::channel();
+        self.to_service.send(PayloadServiceCommand::Resolve(id, kind, tx))?;
+        rx.await.map_err(Into::into)
+    }
+
     /// Sends a message to the service to subscribe to payload events.
     /// Returns a receiver that will receive them.
     pub async fn subscribe(&self) -> Result<PayloadEvents<T>, PayloadBuilderError> {

crates/payload/primitives/src/error.rs

@@ -5,7 +5,7 @@ use alloy_primitives::B256;
 use alloy_rpc_types_engine::{ForkchoiceUpdateError, PayloadError, PayloadStatusEnum};
 use core::error;
 use reth_errors::{BlockExecutionError, ProviderError, RethError};
-use tokio::sync::oneshot;
+use tokio::sync::{mpsc, oneshot};
 
 /// Possible error variants during payload building.
 #[derive(Debug, thiserror::Error)]
@@ -69,6 +69,12 @@ impl From<BlockExecutionError> for PayloadBuilderError {
     }
 }
 
+impl<T> From<mpsc::error::SendError<T>> for PayloadBuilderError {
+    fn from(_: mpsc::error::SendError<T>) -> Self {
+        Self::ChannelClosed
+    }
+}
+
 /// Thrown when the payload or attributes are known to be invalid __before__ processing.
 ///
 /// This is used mainly for