Live Paint: a triple-click matches the first fill of a face clicked again

A triple-click whose clicks land on a face, another face, then the first
face again matched the fill the first click gave that face. It now
matches the fill the face had before the first click that painted it, as
the tool's doc comment and docs/mcp.md say.

- With Space held for the view tools, the Live Paint Bucket outlines no
  face or edge, as a press there paints nothing.
- A scoped livePaint.fill or livePaint.strokeEdge where every face or
  edge reached already has the paint records no undo step; a test covers
  it, and one where only some faces need the paint.
- An MCP test drives the bucket through ui.pointer with mods.space.
- The tool's doc comment and the progress line state the rule.

crates/engine/src/tests/build.rs

@@ -2566,6 +2566,42 @@ fn live_paint_stroke_edge_same_paint_and_width_is_no_op() {
     assert_eq!(history_state(&s).0, before.1.0 + 1);
 }
 
+/// With `scope`, faces and edges that already have the paint (and the width) are skipped: when
+/// every face or edge the call reaches has it, nothing changes, and when some do, only the others
+/// are painted, in one undo step. `count` is every face or edge reached.
+#[test]
+fn live_paint_scoped_fill_and_stroke_skip_parts_with_the_paint() {
+    let mut s = session();
+    let g = live(&mut s);
+    s.execute("livePaint.fill", &json!({"group": g.0, "point": [25, 50], "points": [[25, 50], [125, 50]], "color": "#00ff00"})).unwrap();
+    let edges =
+        s.execute("livePaint.strokeEdge", &json!({"group": g.0, "point": [100, 50], "scope": "samePaint", "color": "#ff0000", "width": 3})).unwrap();
+    redo_waiting_and_saved(&mut s, g);
+    let mut before = snapshot(&s);
+    let same = json!({"group": g.0, "point": [75, 50], "scope": "samePaint", "color": "#00ff00"});
+    assert_eq!(s.execute("livePaint.fill", &same).unwrap()["count"], 3);
+    assert_unchanged(&mut s, &mut before, "a samePaint fill where every face has the paint");
+    let again = json!({"group": g.0, "point": [100, 50], "scope": "samePaint", "color": "#ff0000", "width": 3});
+    assert_eq!(s.execute("livePaint.strokeEdge", &again).unwrap()["count"], edges["count"]);
+    assert_unchanged(&mut s, &mut before, "a samePaint stroke where every edge has the paint and the width");
+    // One face of the three without the paint: only it is filled, in one undo step.
+    let green = Paint::solid(Color::from_hex("#00ff00").unwrap());
+    let red = Paint::solid(Color::from_hex("#ff0000").unwrap());
+    s.execute("livePaint.fill", &json!({"group": g.0, "point": [25, 50], "color": "#ff0000"})).unwrap();
+    let depth = history_state(&s).0;
+    let like = serde_json::to_value(&green).unwrap();
+    let r = s.execute("livePaint.fill", &json!({"group": g.0, "point": [25, 50], "scope": "samePaint", "match": like, "color": "#00ff00"})).unwrap();
+    assert_eq!(r["count"], 3);
+    assert_eq!(history_state(&s).0, depth + 1);
+    let fill_at = |s: &Session, x: f64| vectorcraft_tools::builder::face_at(&node(s, g), Point::new(x, 50.0)).unwrap().appearance.fill_paint();
+    for x in [25.0, 75.0, 125.0] {
+        assert_eq!(fill_at(&s, x), green, "{x}");
+    }
+    s.execute("edit.undo", &json!({})).unwrap();
+    assert_eq!(fill_at(&s, 25.0), red);
+    assert_eq!((fill_at(&s, 75.0), fill_at(&s, 125.0)), (green.clone(), green));
+}
+
 #[test]
 fn live_paint_gap_options_same_values_are_no_op() {
     let mut s = session();