ref impl: Address PR Comments

- var -> const (+ removing som extra copies)
- Rename BlockPreparer interface to Engine
- Remove out of date comment and update safe block

opnode/l1/source.go

@@ -14,10 +14,7 @@ import (
 	"github.com/ethereum/go-ethereum/ethclient"
 )
 
-var WrongChainErr = errors.New("wrong chain")
-var TooDeepReorgErr = errors.New("reorg is too deep")
-var MaxReorgDepth = 500
-var MaxBlocksInL1Range = uint64(100)
+const MaxBlocksInL1Range = uint64(100)
 
 type Source struct {
 	client     *ethclient.Client

opnode/rollup/driver/driver.go

@@ -31,7 +31,7 @@ type Downloader interface {
 	FetchTransactions(ctx context.Context, window []eth.BlockID) ([]*types.Transaction, error)
 }
 
-type BlockPreparer interface {
+type Engine interface {
 	GetPayload(ctx context.Context, payloadId l2.PayloadID) (*l2.ExecutionPayload, error)
 	ForkchoiceUpdate(ctx context.Context, state *l2.ForkchoiceState, attr *l2.PayloadAttributes) (*l2.ForkchoiceUpdatedResult, error)
 	ExecutePayload(ctx context.Context, payload *l2.ExecutionPayload) error

opnode/rollup/driver/step.go

@@ -18,7 +18,7 @@ import (
 
 type outputImpl struct {
 	dl     Downloader
-	l2     BlockPreparer
+	l2     Engine
 	log    log.Logger
 	Config rollup.Config
 }
@@ -176,7 +176,9 @@ func (d *outputImpl) step(ctx context.Context, l2Head eth.BlockID, l2Finalized e
 			return last, fmt.Errorf("failed to extend L2 chain at block %d/%d of epoch %d: %w", i, len(batches), epoch, err)
 		}
 		last = payload.ID()
-		fc.HeadBlockHash = last.Hash // should be safe block, but geth is broken
+		// TODO(Joshua): Update this to handle verifiers + sequencers
+		fc.HeadBlockHash = last.Hash
+		fc.SafeBlockHash = last.Hash
 	}
 
 	return last, nil

opnode/rollup/sync/start.go

@@ -56,7 +56,8 @@ type L2Chain interface {
 
 var WrongChainErr = errors.New("wrong chain")
 var TooDeepReorgErr = errors.New("reorg is too deep")
-var MaxReorgDepth = 500
+
+const MaxReorgDepth = 500
 
 // FindSafeL2Head takes the supplied L2 start block and walks the L2 chain until it finds the first L2 block reachable from the supplied
 // block that is also canonical.