clarified signature: just one class Directory is sufficient;

--- a/src/Pure/System/nodejs.scala	Tue Sep 09 15:37:38 2025 +0200
+++ b/src/Pure/System/nodejs.scala	Tue Sep 09 17:39:04 2025 +0200
@@ -14,65 +14,48 @@
 
   val default_version = "22.17.0"
 
-  def context(
-    platform_context: Isabelle_Platform.Context = Isabelle_Platform.Context(),
-    version: String = default_version
-  ): Context = new Context(platform_context, version)
-
   def setup(
     base_dir: Path,
     platform_context: Isabelle_Platform.Context = Isabelle_Platform.Context(),
     version: String = default_version,
     packages: List[String] = Nil
   ): Directory = {
-    context(platform_context = platform_context, version = version)
-      .setup(base_dir, packages = packages)
+    val platform = platform_context.isabelle_platform
+    val progress = platform_context.progress
+
+    val platform_name =
+      if (platform.is_windows) "win" else if (platform.is_macos) "darwin" else "linux"
+
+    val arch = if (platform.is_arm) "arm64" else "x64"
+    val full_name = "node-v" + version + "-" + platform_name + "-" + arch
+
+    val download_ext = if (platform.is_windows) "zip" else "tar.gz"
+    val download_url = "https://nodejs.org/dist/v" + version + "/" + full_name + "." + download_ext
+
+    Isabelle_System.with_tmp_file("node", ext = download_ext) { archive =>
+      progress.echo("Getting Node.js ...")
+      Isabelle_System.download_file(download_url, archive)
+
+      progress.echo("Installing node ...")
+      Isabelle_System.extract(archive, base_dir)
+      val node_dir = new Directory(platform_context, base_dir + Path.basic(full_name))
+
+      for (name <- packages) node_dir.install(name)
+
+      node_dir
+    }
   }
 
-  class Context private[Nodejs](val platform_context: Isabelle_Platform.Context, version: String) {
+  class Directory private[Nodejs](
+    val platform_context: Isabelle_Platform.Context,
+    val path: Path
+  ) {
     def platform: Isabelle_Platform = platform_context.isabelle_platform
     def progress: Progress = platform_context.progress
 
-    override def toString: String =
-      "node-" + version + "-" + platform.ISABELLE_PLATFORM(windows = true, apple = true)
-
-    def arch: String = if (platform.is_arm) "arm64" else "x64"
-
-    def platform_name: String =
-      if (platform.is_windows) "win" else if (platform.is_macos) "darwin" else "linux"
-
-    def full_name: String = "node-v" + version + "-" + platform_name + "-" + arch
-
-    def download_ext: String = if (platform.is_windows) "zip" else "tar.gz"
-
-    def download_url: String =
-      "https://nodejs.org/dist/v" + version + "/" + full_name + "." + download_ext
-
-    def setup(base_dir: Path, packages: List[String] = Nil): Directory = {
-      Isabelle_System.with_tmp_file("node", ext = download_ext) { archive =>
-        progress.echo("Getting Node.js ...")
-        Isabelle_System.download_file(download_url, archive)
+    override def toString: String = path.file_name
 
-        progress.echo("Installing node ...")
-        Isabelle_System.extract(archive, base_dir)
-        val node_dir = new Directory(this, base_dir + Path.basic(full_name))
-
-        for (name <- packages) node_dir.install(name)
-
-        node_dir
-      }
-    }
-  }
-
-  class Directory private[Nodejs](val context: Context, val path: Path) {
-    override def toString: String = path.toString
-
-    def platform_context: Isabelle_Platform.Context = context.platform_context
-    def progress: Progress = context.progress
-
-    def bin_dir: Path =
-      if (platform_context.isabelle_platform.is_windows) path
-      else path + Path.basic("bin")
+    def bin_dir: Path = if (platform.is_windows) path else path + Path.basic("bin")
 
     def path_setup: String =
       "export PATH=" + Bash.string(platform_context.standard_path(bin_dir)) + """:"$PATH""""