Maps are editor-built scenes: [Tool] Playground/Crag, headless rebuild for agents

scenes/maps/playground.tscn and crag.tscn are generated by the map scripts' Rebuild (inspector
button, or godot-mono --headless --path . tools/rebuild_maps.tscn) and loaded as saved by the game,
so hand edits stick. The crag route is saved as Marker3D nodes and crag_spike checks the saved
scene. Layout verified identical to the code-built one (tools/map_dump.tscn).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/MapScene.cs

@@ -0,0 +1,80 @@
+using Godot;
+using System.Collections.Generic;
+
+// Shared plumbing for the editor-built maps (Playground, Crag). Each map is the ROOT of its own scene
+// (scenes/maps/*.tscn) with a [Tool] script whose Rebuild() regenerates every child from code and
+// gives it to the scene (Owner = the map root) so it is saved into the .tscn like hand-made nodes.
+// The game never regenerates: it loads what was saved, so edits made in the editor stick (until the
+// next Rebuild, which replaces ALL children). Rebuild from the inspector button with the map scene
+// open, or headless for agents: godot-mono --headless --path . tools/rebuild_maps.tscn
+public static class MapScene
+{
+    public const string PropGroup = "prop";
+
+    // The inspector button only works with the map scene itself open (nodes owned by an instanced
+    // sub-scene's root aren't saved into the outer scene).
+    public static bool CanRebuildInEditor(Node map)
+    {
+        if (map.GetTree()?.EditedSceneRoot == map)
+            return true;
+        GD.PushWarning($"{map.Name}: open its own scene (scenes/maps/) to rebuild it — it's instanced here.");
+        return false;
+    }
+
+    public static void Clear(Node map)
+    {
+        foreach (Node child in map.GetChildren())
+        {
+            map.RemoveChild(child);
+            child.Free();
+        }
+    }
+
+    // Every generated node belongs to the map scene; children of instanced sub-scenes (e.g. a
+    // teleport marker) keep their own owner.
+    public static void Adopt(Node map)
+    {
+        foreach (Node child in map.GetChildren())
+            Adopt(map, child);
+    }
+
+    private static void Adopt(Node root, Node node)
+    {
+        if (node.Owner == null)
+            node.Owner = root;
+        if (node.SceneFilePath != "")
+            return;
+        foreach (Node child in node.GetChildren())
+            Adopt(root, child);
+    }
+
+    public static void MarkUnsaved()
+    {
+#if TOOLS
+        if (Engine.IsEditorHint())
+            EditorInterface.Singleton.MarkSceneAsUnsaved();
+#endif
+    }
+
+    // Runtime: the dynamic props (group "prop") and where they start, for Reset().
+    public static void CollectProps(Node map, List<(RigidBody3D Body, Transform3D Start)> props)
+    {
+        props.Clear();
+        foreach (Node child in map.GetChildren())
+            if (child is RigidBody3D body && body.IsInGroup(PropGroup))
+                props.Add((body, body.GlobalTransform));
+    }
+
+    public static void Reset(List<(RigidBody3D Body, Transform3D Start)> props)
+    {
+        foreach (var (body, start) in props)
+        {
+            if (!GodotObject.IsInstanceValid(body))
+                continue;
+            body.GlobalTransform = start;
+            body.LinearVelocity = Vector3.Zero;
+            body.AngularVelocity = Vector3.Zero;
+            body.ResetPhysicsInterpolation();
+        }
+    }
+}