fix: handle height mismatch between Rollkit (1) and Reth (0)

Use Reth's genesis block hash for forkchoice update when Rollkit
initializes at height 1, ensuring proper block progression without
modifying block numbers.

execution.go

@@ -105,6 +105,38 @@ func (c *EngineAPIExecutionClient) Stop() {
 
 // InitChain initializes the blockchain with genesis information
 func (c *EngineAPIExecutionClient) InitChain(ctx context.Context, genesisTime time.Time, initialHeight uint64, chainID string) (execution_types.Hash, uint64, error) {
+	// For height 1, we need both the genesis state root and to prepare block 1
+	if initialHeight == 1 {
+		// Get genesis state root
+		header, err := c.ethClient.HeaderByNumber(ctx, big.NewInt(0))
+		if err != nil {
+			return execution_types.Hash{}, 0, fmt.Errorf("failed to get genesis block: %w", err)
+		}
+
+		// Now prepare block 1 by setting forkchoice to genesis
+		genesisHash := header.Hash()
+		var forkchoiceResult engine.ForkChoiceResponse
+		err = c.engineClient.CallContext(ctx, &forkchoiceResult, "engine_forkchoiceUpdatedV3",
+			engine.ForkchoiceStateV1{
+				HeadBlockHash:      genesisHash,
+				SafeBlockHash:      genesisHash,
+				FinalizedBlockHash: genesisHash,
+			},
+			engine.PayloadAttributes{
+				Timestamp:             uint64(genesisTime.Unix()),
+				Random:                common.Hash{},
+				SuggestedFeeRecipient: c.feeRecipient,
+				BeaconRoot:            &genesisHash,
+				Withdrawals:           []*types.Withdrawal{},
+			},
+		)
+		if err != nil {
+			return execution_types.Hash{}, 0, fmt.Errorf("engine_forkchoiceUpdatedV3 failed: %w", err)
+		}
+
+		return execution_types.Hash(header.Root[:]), uint64(1000000), nil
+	}
+
 	var forkchoiceResult engine.ForkChoiceResponse
 	err := c.engineClient.CallContext(ctx, &forkchoiceResult, "engine_forkchoiceUpdatedV3",
 		engine.ForkchoiceStateV1{
@@ -113,7 +145,7 @@ func (c *EngineAPIExecutionClient) InitChain(ctx context.Context, genesisTime ti
 			FinalizedBlockHash: c.genesisHash,
 		},
 		engine.PayloadAttributes{
-			Timestamp:             uint64(genesisTime.Unix()), //nolint:gosec // disable G115
+			Timestamp:             uint64(genesisTime.Unix()),
 			Random:                common.Hash{},
 			SuggestedFeeRecipient: c.feeRecipient,
 			BeaconRoot:            &c.genesisHash,
@@ -134,6 +166,21 @@ func (c *EngineAPIExecutionClient) InitChain(ctx context.Context, genesisTime ti
 		return execution_types.Hash{}, 0, fmt.Errorf("engine_getPayloadV3 failed: %w", err)
 	}
 
+	// submit payload
+	var newPayloadResult engine.PayloadStatusV1
+	err = c.engineClient.CallContext(ctx, &newPayloadResult, "engine_newPayloadV3",
+		payloadResult.ExecutionPayload,
+		[]string{}, // no blob hashes
+		c.genesisHash.Hex(),
+	)
+	if err != nil {
+		return execution_types.Hash{}, 0, fmt.Errorf("new payload submission failed: %w", err)
+	}
+
+	if newPayloadResult.Status != engine.VALID {
+		return execution_types.Hash{}, 0, ErrInvalidPayloadStatus
+	}
+
 	stateRoot := payloadResult.ExecutionPayload.StateRoot
 	rollkitStateRoot := execution_types.Hash(stateRoot[:])