address PR comments

execution/gethexec/express_lane_service.go

@@ -4,6 +4,7 @@
 package gethexec
 
 import (
+	"bytes"
 	"context"
 	"fmt"
 	"sync"
@@ -329,7 +330,10 @@ func (es *expressLaneService) sequenceExpressLaneSubmission(
 	}
 
 	// Check if a duplicate submission exists already, and reject if so.
-	if _, exists := roundInfo.msgAndResultBySequenceNumber[msg.SequenceNumber]; exists {
+	if prev, exists := roundInfo.msgAndResultBySequenceNumber[msg.SequenceNumber]; exists {
+		if bytes.Equal(prev.msg.Signature, msg.Signature) {
+			return nil
+		}
 		return timeboost.ErrDuplicateSequenceNumber
 	}
 

execution/gethexec/express_lane_service_test.go

@@ -317,18 +317,19 @@ func Test_expressLaneService_sequenceExpressLaneSubmission_duplicateNonce(t *tes
 	stubPublisher := makeStubPublisher(els)
 	els.transactionPublisher = stubPublisher
 
-	msg := buildValidSubmissionWithSeqAndTx(t, 0, 2, types.NewTx(&types.DynamicFeeTx{Data: []byte{1}}))
+	msg1 := buildValidSubmissionWithSeqAndTx(t, 0, 2, types.NewTx(&types.DynamicFeeTx{Data: []byte{1}}))
+	msg2 := buildValidSubmissionWithSeqAndTx(t, 0, 2, types.NewTx(&types.DynamicFeeTx{Data: []byte{2}}))
 	var wg sync.WaitGroup
 	wg.Add(3) // We expect only of the below two to return with an error here
 	var err1, err2 error
 	go func(w *sync.WaitGroup) {
 		w.Done()
-		err1 = els.sequenceExpressLaneSubmission(ctx, msg)
+		err1 = els.sequenceExpressLaneSubmission(ctx, msg1)
 		wg.Done()
 	}(&wg)
 	go func(w *sync.WaitGroup) {
 		w.Done()
-		err2 = els.sequenceExpressLaneSubmission(ctx, msg)
+		err2 = els.sequenceExpressLaneSubmission(ctx, msg2)
 		wg.Done()
 	}(&wg)
 	wg.Wait()