fix: gloas from genesis

- Fix forkchoice update sending zero-hash head to EL at genesis by reading
  latest_block_hash from state when the genesis bid hashes are all zeros
- Simplify genesis block construction — the genesis block body is empty per
  spec, remove the incorrect bid-copying logic and body root override in
  initialize_beacon_state_from_eth1

consensus/fork_choice/src/fork_choice.rs

@@ -416,11 +416,24 @@ where
 
         let (execution_status, execution_payload_parent_hash, execution_payload_block_hash) =
             if let Ok(signed_bid) = anchor_block.message().body().signed_execution_payload_bid() {
-                // Gloas: execution status is irrelevant post-Gloas; payload validation
+                // At Gloas genesis the block bid is empty (all zeros) per spec, but the
-                // is decoupled from beacon blocks.
+                // state holds the EL genesis hash in `latest_block_hash`. Use it so the
+                // first forkchoice update sends a valid head to the EL.
+                let parent_hash = if anchor_block.slot() == spec.genesis_slot
+                    && anchor_state.slot() == spec.genesis_slot
+                    && signed_bid.message.parent_block_hash.into_root().is_zero()
+                    && signed_bid.message.block_hash.into_root().is_zero()
+                {
+                    *anchor_state
+                        .latest_block_hash()
+                        .map_err(Error::BeaconStateError)?
+                } else {
+                    signed_bid.message.parent_block_hash
+                };
+
                 (
                     ExecutionStatus::irrelevant(),
-                    Some(signed_bid.message.parent_block_hash),
+                    Some(parent_hash),
                     Some(signed_bid.message.block_hash),
                 )
             } else if let Ok(execution_payload) = anchor_block.message().execution_payload() {

consensus/state_processing/src/genesis.rs

@@ -167,19 +167,12 @@ pub fn initialize_beacon_state_from_eth1<E: EthSpec>(
         // Remove intermediate Fulu fork from `state.fork`.
         state.fork_mut().previous_version = spec.gloas_fork_version;
 
-        // The genesis block's bid must have block_hash = 0x00 per spec (empty payload).
         // Retain the EL genesis hash in latest_block_hash and parent_block_hash so the
         // first post-genesis proposer can build on the correct EL head.
         let el_genesis_hash = state.latest_execution_payload_bid()?.block_hash;
         let bid = state.latest_execution_payload_bid_mut()?;
         bid.parent_block_hash = el_genesis_hash;
         bid.block_hash = ExecutionBlockHash::default();
-
-        // Update the `latest_block_header.body_root` so that it matches the body of the
-        // Gloas genesis block, which embeds `state.latest_execution_payload_bid` in its
-        // `signed_execution_payload_bid` field (see `genesis_block`).
-        let genesis_body_root = genesis_block(&state, spec)?.body_root();
-        state.latest_block_header_mut().body_root = genesis_body_root;
     }
 
     // Now that we have our validators, initialize the caches (including the committees)
@@ -191,25 +184,16 @@ pub fn initialize_beacon_state_from_eth1<E: EthSpec>(
     Ok(state)
 }
 
-/// Create an unsigned genesis `BeaconBlock`.
+/// Create an unsigned genesis `BeaconBlock` matching the genesis state.
 ///
-/// Per spec, the genesis block body is empty (all default fields) except for Gloas,
+/// Per spec, the genesis block body is empty (all default fields).
-/// where `body.signed_execution_payload_bid.message` is initialised from
+/// `state.latest_block_header.body_root` is set from `BeaconBlock::empty()`,
-/// `state.latest_execution_payload_bid` so that the first post-genesis proposer can
+/// so this function must return the same empty block to keep roots consistent.
-/// build on the correct execution layer head.
-///
-/// `state.latest_block_header.body_root` is set from this same block's body, so the
-/// two must stay in sync.
 pub fn genesis_block<E: EthSpec>(
-    state: &BeaconState<E>,
+    _genesis_state: &BeaconState<E>,
     spec: &ChainSpec,
 ) -> Result<BeaconBlock<E>, BeaconStateError> {
-    let mut block = BeaconBlock::empty(spec);
+    Ok(BeaconBlock::empty(spec))
-    if let BeaconBlock::Gloas(ref mut gloas_block) = block {
-        let bid = state.latest_execution_payload_bid()?.clone();
-        gloas_block.body.signed_execution_payload_bid.message = bid;
-    }
-    Ok(block)
 }
 
 /// Determine whether a candidate genesis state is suitable for starting the chain.