Treat already known error as success and move to confirmation

chain/evm/provider/rpcclient/multiclient.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"math/big"
+	"strings"
 	"sync"
 	"time"
 
@@ -38,6 +39,7 @@ const (
 
 	// Default timeout for health checks
 	RPCDefaultHealthCheckTimeout = 2 * time.Second
+	AlreadyKnownErrorMessage     = "already known"
 )
 
 // RetryConfig configures retry behavior for RPC operations.
@@ -161,7 +163,14 @@ func NewMultiClient(
 // chain.DeployerKey at chain load (gas_config defaults) or before signing the transaction.
 func (mc *MultiClient) SendTransaction(ctx context.Context, tx *types.Transaction) error {
 	return mc.retryWithBackups(ctx, "SendTransaction", func(ct context.Context, client *ethclient.Client) error {
-		return client.SendTransaction(ct, tx)
+		err := client.SendTransaction(ctx, tx)
+		if isAlreadyKnown(err) {
+			// The exact signed transaction is already in this node's
+			// transaction pool or was previously submitted to it.
+			return nil
+		}
+
+		return err
 	})
 }
 
@@ -561,3 +570,13 @@ func maybeDataErr(err error) error {
 
 	return err
 }
+
+func isAlreadyKnown(err error) bool {
+	if err == nil {
+		return false
+	}
+
+	msg := strings.ToLower(err.Error())
+
+	return strings.Contains(msg, AlreadyKnownErrorMessage)
+}

chain/evm/provider/rpcclient/multiclient_test.go

@@ -497,3 +497,52 @@ func TestMultiClient_EstimateGas_cap(t *testing.T) {
 		})
 	}
 }
+
+func TestIsAlreadyKnown(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name string
+		err  error
+		want bool
+	}{
+		{
+			name: "nil error",
+			err:  nil,
+			want: false,
+		},
+		{
+			name: "generic error containing 'already known'",
+			err:  errors.New("failed to send transaction: already known"),
+			want: true,
+		},
+		{
+			name: "error with uppercase 'Already Known'",
+			err:  errors.New("Already Known"),
+			want: true,
+		},
+		{
+			name: "error with padded 'already known'",
+			err:  errors.New("  already known  "),
+			want: true,
+		},
+		{
+			name: "error with 'already known' in middle",
+			err:  errors.New("operation failed: already known: reason unknown"),
+			want: true,
+		},
+		{
+			name: "error that doesn't match",
+			err:  errors.New("some other error"),
+			want: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			got := isAlreadyKnown(tt.err)
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}