add initial electra spec

specs/electra/builder.md

@@ -0,0 +1,36 @@
+# Electra -- Builder Specification
+
+## Introduction
+
+This is the modification of the builder specification accompanying the Electra upgrade.
+
+## Containers
+
+### Extended containers
+
+#### `ExecutionPayloadHeader`
+
+See [`ExecutionPayloadHeader`](https://github.com/ethereum/consensus-specs/blob/dev/specs/electra/beacon-chain.md#executionpayloadheader) in Electra consensus specs.
+
+Note: `ExecutionPayloadAndBlobsBundle` and `BuilderBid` and `SignedBuilderBid` types are updated indirectly.
+
+##### `BlindedBeaconBlockBody`
+
+Note: `BlindedBeaconBlock` and `SignedBlindedBeaconBlock` types are updated indirectly.
+
+```python
+class BlindedBeaconBlockBody(Container):
+    randao_reveal: BLSSignature
+    eth1_data: Eth1Data
+    graffiti: Bytes32
+    proposer_slashings: List[ProposerSlashing, MAX_PROPOSER_SLASHINGS]
+    attester_slashings: List[AttesterSlashing, MAX_ATTESTER_SLASHINGS]
+    attestations: List[Attestation, MAX_ATTESTATIONS]
+    deposits: List[Deposit, MAX_DEPOSITS]
+    voluntary_exits: List[SignedVoluntaryExit, MAX_VOLUNTARY_EXITS]
+    sync_aggregate: SyncAggregate
+    execution_payload_header: ExecutionPayloadHeader  # [Modified in Electra]
+    bls_to_execution_changes: List[SignedBLSToExecutionChange, MAX_BLS_TO_EXECUTION_CHANGES]
+    blob_kzg_commitments: List[KZGCommitment, MAX_BLOB_COMMITMENTS_PER_BLOCK]
+    consolidations: List[SignedConsolidation, MAX_CONSOLIDATIONS]  # [New in Electra]
+```