fix(error): map missing object errors

error.go

@@ -15,3 +15,7 @@ type Error struct {
 func (e *Error) Error() string {
 	return fmt.Sprintf("code: %d, message: %s", e.Code, e.Message)
 }
+
+func (e *Error) Is(target error) bool {
+	return e != nil && target == ErrObjectNotFound && e.Code == 430004
+}

error_test.go

@@ -0,0 +1,31 @@
+package sdk
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+)
+
+func TestErrorIsObjectNotFound(t *testing.T) {
+	if !errors.Is(&Error{Code: 430004}, ErrObjectNotFound) {
+		t.Fatal("expected 430004 to match ErrObjectNotFound")
+	}
+	wrapped := fmt.Errorf("get folder info: %w", &Error{Code: 430004})
+	if !errors.Is(wrapped, ErrObjectNotFound) {
+		t.Fatal("expected wrapped 430004 to match ErrObjectNotFound")
+	}
+	var sdkErr *Error
+	if !errors.As(wrapped, &sdkErr) || sdkErr.Code != 430004 {
+		t.Fatal("expected wrapped error to preserve *Error")
+	}
+	if errors.Is(&Error{Code: 430005}, ErrObjectNotFound) {
+		t.Fatal("unexpected object-not-found match")
+	}
+	if errors.Is(&Error{Code: 430004}, errors.New("object not found")) {
+		t.Fatal("unexpected match for a different target")
+	}
+	var nilErr *Error
+	if errors.Is(nilErr, ErrObjectNotFound) {
+		t.Fatal("unexpected match for a nil error")
+	}
+}