Merge branch 'pr/662' into batch1

# Conflicts:
#	crates/engine/src/cmd/object.rs

docs/mcp.md

@@ -58,7 +58,9 @@ so inspect the document before retrying. The next request re-establishes the con
 
 Points (1/72 in), y down, in **spread** space: on a single-page spread the page's top-left is (0, 0); on a facing
 spread the right page starts at x = page width. `inspect_document` lists page bounds per spread. Page indices in
-`render_page` / `export_png` are 0-based. `pointer` events in connected mode may use `"space": "screen"` (egui points,
+`render_page` / `export_png` are 0-based. Commands that create items take `spread`: a body spread index, or
+`{"kind": "parent", "index": 0}` for a parent spread (its index in `parents` of `inspect_document`); any other
+value is an error. `pointer` events in connected mode may use `"space": "screen"` (egui points,
 see `ui_inspect` → `canvasRect`).
 
 ## Text offsets