specify the max blobs per block with each payload

specs/electra/fork-choice.md

@@ -0,0 +1,37 @@
+# Electra -- Fork Choice
+
+## Table of contents
+<!-- TOC -->
+<!-- START doctoc generated TOC please keep comment here to allow auto update -->
+<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
+
+- [Introduction](#introduction)
+- [Containers](#containers)
+- [Helpers](#helpers)
+  - [Extended `PayloadAttributes`](#extended-payloadattributes)
+
+<!-- END doctoc generated TOC please keep comment here to allow auto update -->
+<!-- /TOC -->
+
+## Introduction
+
+This is the modification of the fork choice accompanying the Electra upgrade.
+
+## Containers
+
+## Helpers
+
+### Extended `PayloadAttributes`
+
+`PayloadAttributes` is extended with the maximum number of blobs per block.
+
+```python
+@dataclass
+class PayloadAttributes(object):
+    timestamp: uint64
+    prev_randao: Bytes32
+    suggested_fee_recipient: ExecutionAddress
+    withdrawals: Sequence[Withdrawal]
+    parent_beacon_block_root: Root
+    max_blobs_per_block: uint64  # [New in Electra]
+```

specs/electra/validator.md

@@ -139,6 +139,7 @@ def prepare_execution_payload(state: BeaconState,
         suggested_fee_recipient=suggested_fee_recipient,
         withdrawals=withdrawals,
         parent_beacon_block_root=hash_tree_root(state.latest_block_header),
+        max_blobs_per_block=MAX_BLOBS_PER_BLOCK,  # [New in Electra]
     )
     return execution_engine.notify_forkchoice_updated(
         head_block_hash=parent_hash,