Add safe immutable directory promotion

internal/fileops/rename_noreplace_other.go

@@ -0,0 +1,9 @@
+//go:build !linux
+
+package fileops
+
+import "fmt"
+
+func renameDirectoryNoReplace(_, _ string) error {
+	return fmt.Errorf("atomic no-replace directory rename is unsupported on this platform")
+}