Add sync protocol changes

pysetup/spec_builders/eip7732.py

@@ -19,3 +19,10 @@ def hardcoded_custom_type_dep_constants(cls, spec_object) -> Dict[str, str]:
             'PTC_SIZE': spec_object.preset_vars['PTC_SIZE'].value,
             'MAX_PAYLOAD_ATTESTATIONS': spec_object.preset_vars['MAX_PAYLOAD_ATTESTATIONS'].value,
         }
+
+    @classmethod
+    def hardcoded_ssz_dep_constants(cls) -> Dict[str, str]:
+        constants = {
+            'EXECUTION_PAYLOAD_GINDEX': 'GeneralizedIndex(26)',
+        }
+        return {**super().hardcoded_ssz_dep_constants(), **constants}

specs/_features/eip7732/light-client/sync-protocol.md

@@ -0,0 +1,20 @@
+# EIP-7732 Light Client -- Sync Protocol
+
+**Notice**: This document is a work-in-progress for researchers and implementers.
+
+## 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 -->
+
+- [Modified Constants](#modified-constants)
+
+<!-- END doctoc generated TOC please keep comment here to allow auto update -->
+<!-- /TOC -->
+
+## Modified Constants
+
+| Name | Value |
+| - | - |
+| `EXECUTION_PAYLOAD_GINDEX` | `get_generalized_index(BeaconBlockBody, 'signed_execution_payload_header')` (= 25) |