Fix Process same-slot slashings before builder payments in Gloas #4561

Author: 0xc0de42

specs/gloas/beacon-chain.md

@@ -729,8 +729,6 @@ def process_builder_pending_payments(state: BeaconState) -> None:
 
 ```python
 def process_block(state: BeaconState, block: BeaconBlock) -> None:
-    process_block_header(state, block)
-    # [Modified in Gloas:EIP7732]
     process_withdrawals(state)
     # [Modified in Gloas:EIP7732]
     # Removed `process_execution_payload`
@@ -741,6 +739,8 @@ def process_block(state: BeaconState, block: BeaconBlock) -> None:
     # [Modified in Gloas:EIP7732]
     process_operations(state, block.body)
     process_sync_aggregate(state, block.body.sync_aggregate)
+    # [Modified in Gloas:EIP7732]
+    process_block_header(state, block)
 ```
 
 #### Withdrawals

tests/core/pyspec/eth2spec/test/gloas/block_processing/test_process_execution_payload_bid.py

@@ -1,3 +1,6 @@
+import random
+from eth2spec.test.helpers.state import next_epoch
+
 from eth2spec.test.context import (
     always_bls,
     spec_state_test,
@@ -349,6 +352,48 @@ def test_process_execution_payload_bid_slashed_builder(spec, state):
     yield from run_execution_payload_bid_processing(spec, state, block, valid=False)
 
 
+@with_gloas_and_later
+@spec_state_test
+def test_process_block_then_slash_non_timely_builder(spec, state):
+    """
+    Test proposer is rewarded if builder is slashed after a successful bid.
+    This test case tests the third fork choice - "Empty", The beacon block has been included on-chain, but the committed execution payload has not.
+    The beacon block proposer received payment from the corresponding builder. 
+    """
+
+    # Advance to a state past genesis so the builder is active
+    next_epoch(spec, state)
+    next_epoch(spec, state)
+    state.slot += random.randrange(spec.SLOTS_PER_EPOCH)
+
+    # Prepare block and assign a builder who is not the proposer
+    block, builder_index = prepare_block_with_non_proposer_builder(spec, state)
+    proposer_index = block.proposer_index
+
+    # Give builder enough balance for the bid to succeed
+    value = spec.Gwei(1_000_000)
+    state.balances[builder_index] = value + spec.MIN_ACTIVATION_BALANCE
+
+    # Prepare and insert a valid signed bid from the builder
+    signed_bid = prepare_signed_execution_payload_bid(
+        spec,
+        state,
+        builder_index=builder_index,
+        value=value,
+        slot=block.slot,
+        parent_block_root=block.parent_root,
+    )
+    # block.body.signed_execution_payload_bid = signed_bid
+
+    # Capture proposer balance before processing
+    pre_balance = state.balances[proposer_index]
+
+    spec.process_block(state, block)
+
+    post_balance = state.balances[proposer_index]
+    assert post_balance >= pre_balance + value, "Proposer did not receive builder's slashed bid value"
+
+
 @with_gloas_and_later
 @spec_state_test
 def test_process_execution_payload_bid_self_build_non_zero_value(spec, state):