From 869e5a22d96cc50a36953c27777070532ea01aae Mon Sep 17 00:00:00 2001
From: samliok <samliok@stanford.edu>
Date: Mon, 17 Aug 2026 22:05:49 -0400
Subject: [PATCH] double start nit

---
 instance.go      | 8 ++++++--
 instance_test.go | 2 +-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/instance.go b/instance.go
index 39d82e3e..4a4fd8a7 100644
--- a/instance.go
+++ b/instance.go
@@ -5,6 +5,7 @@ package simplex
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"math"
 	"sync"
@@ -19,6 +20,8 @@ import (
 	"go.uber.org/zap"
 )
 
+var errAlreadyStarted = errors.New("instance already started")
+
 const (
 	// tickInterval is the interval at which the instance will call AdvanceTime on the current epoch or non-validator.
 	tickInterval = time.Millisecond * 100
@@ -34,6 +37,8 @@ type Config struct {
 	PlatformChain PlatformChain
 	// Broadcaster is the interface to broadcast messages to other nodes in the network.
 	Broadcaster Broadcaster
+	// Sender is an interface to send messages to a specific node in the network
+	Sender Sender
 	// CryptoOps is the interface to the cryptographic operations needed by the simplex instance.
 	CryptoOps CryptoOps
 	// WalCreator is the interface to create new write-ahead logs for the simplex instance.
@@ -41,7 +46,6 @@ type Config struct {
 	// Storage is the interface to the block storage layer for the simplex instance.
 	Storage        Storage
 	Logger         common.Logger
-	Sender         Sender
 	WALs           []wal.DeletableWAL
 	VM             VM
 	ICMETransition metadata.ICMEpochTransition
@@ -94,7 +98,7 @@ func (i *Instance) Start(ctx context.Context) error {
 	defer i.lock.Unlock()
 
 	if i.started {
-		return fmt.Errorf("instance already started")
+		return errAlreadyStarted
 	}
 
 	i.started = true
diff --git a/instance_test.go b/instance_test.go
index 5d22517f..5ad935f4 100644
--- a/instance_test.go
+++ b/instance_test.go
@@ -612,7 +612,7 @@ func TestInstanceDoubleStartFails(t *testing.T) {
 	require.NoError(t, inst.Start(t.Context()))
 	t.Cleanup(inst.Stop)
 
-	require.ErrorContains(t, inst.Start(t.Context()), "instance already started")
+	require.ErrorIs(t, inst.Start(t.Context()), errAlreadyStarted)
 }
 
 func TestNonValidatorSkipsMSMVerification(t *testing.T) {