feat(editor): open with a single empty starter frame

A fresh launch seeded the demo `sample()` document — a Frame with
a 'Hello OpenPencil' title and a 'Click me' button group. New
`EditorState::starter()` returns just one empty Frame (selected),
and both hosts open with it; `sample()` stays as the widget-test
fixture. input_tests retarget their `n11` selections to the
starter frame's `n10`.

crates/op-editor-core/src/host_support.rs

@@ -21,9 +21,8 @@ impl EditorState {
     /// containing a Text `n11` and a Group `n12` (`n13` blue rect +
     /// `n14` text). Selection anchors on `n11`.
     ///
-    /// Mirrors the historical shell-core `Document::sample()` fixture
-    /// so the native host opens with identical content after the
-    /// migration onto `EditorState`.
+    /// This is the widget-test fixture. The native host opens with
+    /// [`EditorState::starter`] (a single empty Frame) instead.
     pub fn sample() -> Self {
         let src = r##"{
             "version": "0.8.0",
@@ -55,6 +54,29 @@ impl EditorState {
         state
     }
 
+    /// Build the document a fresh launch opens with — a single empty
+    /// starter Frame `n10` (white fill, 1-px black stroke), selected
+    /// so the user can immediately resize / move it or drop nodes
+    /// inside. No demo decoration.
+    pub fn starter() -> Self {
+        let src = r##"{
+            "version": "0.8.0",
+            "children": [
+              {"type":"frame","id":"n10","name":"Frame",
+               "x":40,"y":40,"width":360,"height":240,
+               "fill":[{"type":"solid","color":"#FFFFFF"}],
+               "stroke":{"thickness":1,"fill":[{"type":"solid","color":"#000000"}]},
+               "children":[]}
+            ]
+        }"##;
+        let doc = jian_ops_schema::load_str(src)
+            .expect("EditorState::starter() fixture parses")
+            .value;
+        let mut state = Self::from_document(doc);
+        state.set_single_selection(NodeId::new("n10"));
+        state
+    }
+
     /// Spawn a fresh leaf node for the active shape / frame / text
     /// tool at `(doc_x, doc_y)`, sized `init_w × init_h`. Returns the
     /// new node's id on success; `None` for `Select` / `Hand` (no
@@ -200,6 +222,17 @@ mod tests {
         assert_eq!(s.max_node_id(), 14);
     }
 
+    #[test]
+    fn starter_is_a_single_empty_frame_with_it_selected() {
+        let s = EditorState::starter();
+        // Exactly one top-level node — the starter Frame. The
+        // `max_node_id() == 10` check proves no demo children:
+        // the n11..n14 sample tree would lift it to 14.
+        assert_eq!(s.doc.children.len(), 1);
+        assert_eq!(s.max_node_id(), 10);
+        assert_eq!(s.selection.anchor, NodeId::new("n10"));
+    }
+
     #[test]
     fn create_node_for_tool_spawns_a_rect_and_returns_its_id() {
         let mut s = EditorState::new();

crates/op-host-native/src/widget_host.rs

@@ -373,7 +373,9 @@ pub(in crate::widget_host) struct ComponentBrowserDragState {
 
 impl WidgetHostNative {
     pub fn new() -> Self {
-        let editor_state = op_editor_core::EditorState::sample();
+        // A fresh launch opens with a single empty starter Frame —
+        // see `EditorState::starter`.
+        let editor_state = op_editor_core::EditorState::starter();
         // Seed the render scene once up front; subsequent frames
         // re-derive only when `editor_state_dirty` is set.
         let layout_scene = op_pen_loader::editor_state_to_layout_scene(&editor_state);

crates/op-host-native/src/widget_host/input_tests.rs

@@ -50,7 +50,7 @@ fn escape_closes_one_overlay_per_press_in_priority_order() {
     host.editor_state_mut().editor_ui.fill_type_picker_open = true;
     host.editor_state_mut().chat.focused = true;
     host.editor_state_mut()
-        .set_single_selection(NodeId::new("n11"));
+        .set_single_selection(NodeId::new("n10"));
 
     // 1. Property focus clears first.
     assert!(host.apply_escape());
@@ -92,21 +92,21 @@ fn backspace_with_property_draft_does_not_delete_selected() {
     // char from the draft, not delete the selected node.
     let mut host = WidgetHostNative::new();
     host.editor_state_mut()
-        .set_single_selection(NodeId::new("n11"));
+        .set_single_selection(NodeId::new("n10"));
     host.editor_state_mut().ui.property_focus = Some(PropertyFocus::PositionX);
     host.editor_state_mut().ui.property_input_draft = "123".to_string();
 
     assert!(host.apply_backspace());
     assert_eq!(host.editor_state().ui.property_input_draft, "12");
     // Selection must be untouched.
-    assert_eq!(host.editor_state().selection.anchor, NodeId::new("n11"));
+    assert_eq!(host.editor_state().selection.anchor, NodeId::new("n10"));
 }
 
 #[test]
 fn backspace_without_focus_deletes_selected() {
     let mut host = WidgetHostNative::new();
     host.editor_state_mut()
-        .set_single_selection(NodeId::new("n11"));
+        .set_single_selection(NodeId::new("n10"));
     host.editor_state_mut().ui.property_focus = None;
     host.editor_state_mut().chat.focused = false;
 

crates/op-host-web/src/widget_host.rs

@@ -157,7 +157,9 @@ pub(in crate::widget_host) struct LayerDragState {
 
 impl WidgetHost {
     pub fn new() -> Self {
-        let editor_state = op_editor_core::EditorState::sample();
+        // A fresh launch opens with a single empty starter Frame —
+        // see `EditorState::starter`.
+        let editor_state = op_editor_core::EditorState::starter();
         // Seed the render scene once up front; subsequent frames
         // re-derive only when `editor_state_dirty` is set.
         let layout_scene = op_pen_loader::editor_state_to_layout_scene(&editor_state);