MCP: copy_nodes, and room for groups made round new nodes (#434)

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

MCP.md

@@ -106,9 +106,18 @@ it. One Ctrl+Z takes the whole call back.
   Nodes that belong together go into a group (`add_group`), with a comment on what they do
   (`add_comment`). Both take the nodes they are about rather than a box: a group is drawn around
   them, a comment just above — below them where another node or a group's title bar stands above —
-  and when the call arranges its nodes they follow them there, still in the same undo step. The
+  and when the call arranges its nodes they follow them there, still in the same undo step. A
+  group made round new nodes alone gets room as they are arranged: a node or another such group
+  that would stand in it goes below it, so it holds its own nodes only. The
   group is the one *Group* in the graph's menu draws around a selection. `lint_graph` also counts
   comments a node lies on (`coveredNotes`), which `fit_group` puts back by their nodes.
+- **Copying nodes.** `copy_nodes` copies nodes into the same graph or another, as Ctrl+C and
+  Ctrl+V do: with the links between them and the groups and comments about them alone. Each copy
+  is named by the id of its original (`"$copy.<id>"`), so later steps can link it. Without `x`
+  and `y` the copies are arranged like new nodes, with them the copy keeps its layout. Nodes the
+  other graph cannot hold are refused by name, by the same rule the graph tab pastes with. The
+  variables a copied Variables node reads from its behavior come along into the other behavior,
+  with their default, *Keep* and *Private*. One declared there in another kind is refused.
 - **Silent music.** A pattern plays nothing without an instrument, and an instrument sounds only
   the notes its Notes nodes take in (C4 to B4 in a new one). Nothing else says so. `get_asset` lists
   under `silent` what of a pattern, a song or a composition is not heard: all of it for want of an
@@ -152,7 +161,7 @@ for an area or for command names asked for.
 | assets | `create_asset`, `add_file_asset`, `rename_asset`, `duplicate_asset`, `delete_asset`, `set_asset_property`, `reset_asset_property`, `set_start_scene`, `set_machine_scope`, `set_machine_start`, `set_variables_scope`, `set_variables_persistent`, `make_project_asset` |
 | variables | `add_variable`, `remove_variable`, `rename_variable`, `move_variable`, `set_variable_kept`, `set_variable_private`, `add_struct_field`, `remove_struct_field`, `rename_struct_field`, `move_struct_field`, `set_struct_type`, `make_struct_type`, `set_list_item_type`, `make_list_item_type` |
 | objects | `place_asset`, `remove_objects`, `move_object`, `reorder_object`, `set_editor_offset`, `rename_object`, `set_override`, `clear_override`, `apply_override_to_asset`, `apply_override_to_container`, `revert_override_to_container`, `apply_position_to_container`, `revert_position_to_container`, `set_parent`, `group_objects`, `set_object_group`, `rename_object_group`, `ungroup_objects`, `create_container`, `unpack_container`, `add_collider`, `add_rigidbody`, `add_joint`, `fit_collider` |
-| graphs | `add_node`, `arrange_graph`, `remove_node`, `move_node`, `set_node_param`, `collapse_nodes`, `resize_node`, `connect`, `disconnect`, `fold_edge`, `name_transition`, `add_group`, `add_comment`, `fit_group`, `edit_annotation`, `remove_annotation`, `add_port`, `repoint_port`, `remove_port`, `rename_port`, `move_port`, `set_port_write`, `set_port_machine`, `set_port_default`, `set_node_struct_type`, `split_output`, `set_list_node_type` |
+| graphs | `add_node`, `copy_nodes`, `arrange_graph`, `remove_node`, `move_node`, `set_node_param`, `collapse_nodes`, `resize_node`, `connect`, `disconnect`, `fold_edge`, `name_transition`, `add_group`, `add_comment`, `fit_group`, `edit_annotation`, `remove_annotation`, `add_port`, `repoint_port`, `remove_port`, `rename_port`, `move_port`, `set_port_write`, `set_port_machine`, `set_port_default`, `set_node_struct_type`, `split_output`, `set_list_node_type` |
 | animation | `set_animation_root`, `add_animation_track`, `remove_animation_tracks`, `retarget_animation_track`, `set_track_relative`, `set_animation_key`, `set_key_easing`, `remove_animation_keys`, `move_animation_keys`, `shift_animation_frames`, `key_straight_run`, `set_curve_points` |
 | textures | `add_frame`, `set_frame_rect`, `rename_frame`, `remove_frame`, `slice_frames`, `set_nine_slice`, `set_sort_line`, `set_frame_collision` |
 | tiles | `add_tile_picture`, `remove_tile_picture`, `move_tile_picture`, `paint_tiles`, `add_tilemap_layer`, `duplicate_tilemap_layer`, `remove_tilemap_layer`, `move_tilemap_layer`, `set_tilemap_layer`, `resize_placed_tilemap` |
@@ -267,6 +276,10 @@ What is behind it on the server, and the routes it uses: [API](API), [Developmen
   undo step, `arrange_graph`, what the editor shows after a call (and
   the scene switch inside the undo step, and nothing with *Follow agent* off), the reading tools
   and the catalog (every area in full under the size an answer is cut at).
+- `tests/editor/agent-copy.test.ts`: nodes copied into another behavior with their links, a group
+  and a comment, a variable carried along and later steps linking the copies, all taken back by one
+  undo; a copy placed by hand keeping its layout; nodes a shader cannot hold and a variable of
+  another kind refused.
 - `tests/editor/agent-catalog.test.ts`: a Variables node reading a variable once `add_port` names
   it (and refusing a name it does not know), a group and a comment fitted to the nodes after the
   call arranged them, a field of a Struct asset reaching the variables of that type, a container's