fix(op-preimage): preserve read and write close errors

op-preimage/filechan.go

@@ -46,10 +46,10 @@ func (rw *ReadWritePair) Writer() *os.File {
 func (rw *ReadWritePair) Close() error {
 	var combinedErr error
 	if err := rw.r.Close(); err != nil {
-		combinedErr = errors.Join(fmt.Errorf("failed to close reader: %w", err))
+		combinedErr = errors.Join(combinedErr, fmt.Errorf("failed to close reader: %w", err))
 	}
 	if err := rw.w.Close(); err != nil {
-		combinedErr = errors.Join(fmt.Errorf("failed to close writer: %w", err))
+		combinedErr = errors.Join(combinedErr, fmt.Errorf("failed to close writer: %w", err))
 	}
 	return combinedErr
 }

op-preimage/filechan_test.go

@@ -0,0 +1,25 @@
+package preimage
+
+import (
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestReadWritePairCloseJoinsReaderAndWriterErrors(t *testing.T) {
+	reader, err := os.CreateTemp(t.TempDir(), "reader")
+	require.NoError(t, err)
+	writer, err := os.CreateTemp(t.TempDir(), "writer")
+	require.NoError(t, err)
+
+	require.NoError(t, reader.Close())
+	require.NoError(t, writer.Close())
+
+	err = NewReadWritePair(reader, writer).Close()
+	require.Error(t, err)
+
+	errMsg := err.Error()
+	require.Contains(t, errMsg, "failed to close reader")
+	require.Contains(t, errMsg, "failed to close writer")
+}