M8: an icon double-click becomes the range anchor

A Shift-double-click on a layer's icon leaves only that layer selected, but the range anchor stayed on the layer clicked before, which was no longer selected, so the next Shift-click toggled instead of selecting a range. The icon branch now makes its layer the anchor.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Model-Effort: Opus 5.5 drove; Fable 5.2 queued; Sonnet 5.5 measured and wrote at medium

crates/ui-egui/src/layers_behaviour_tests.rs

@@ -914,3 +914,27 @@ fn an_icon_double_click_keeps_its_selection_when_a_modifier_is_held() {
     let v = &u.app.session.ds().unwrap().view;
     assert_ne!((v.cx, v.zoom), before, "the view frames the layer");
 }
+
+/// A Shift-double-click on an icon leaves just that layer selected, and it becomes the anchor: the
+/// next Shift-click selects the range from it, not a toggle.
+#[test]
+fn an_icon_double_click_becomes_the_range_anchor() {
+    let (mut u, [a, b, c, d]) = four();
+    u.frame(vec![]);
+    let a_row = u.row_at(a);
+    click(&mut u, a_row, Modifiers::NONE);
+    let icon = icon_of(&mut u, b);
+    for _ in 0..2 {
+        for pressed in [true, false] {
+            let e = Event::PointerButton { pos: icon, button: egui::PointerButton::Primary, pressed, modifiers: SHIFT };
+            u.frame_with(vec![Event::PointerMoved(icon), e], SHIFT);
+        }
+    }
+    for _ in 0..30 {
+        u.frame(vec![]);
+    }
+    assert_eq!(u.app.session.selection(), vec![b], "the icon's layer is all that is selected");
+    let d_row = u.row_at(d);
+    click(&mut u, d_row, SHIFT);
+    assert_eq!(sorted(u.app.session.selection()), sorted(vec![b, c, d]), "the range from the icon's layer");
+}

crates/ui-egui/src/panels/layers.rs

@@ -1271,6 +1271,8 @@ fn layers(app: &mut FigApp, ui: &mut Ui) {
                     app.run("view.zoomSelection", json!({}));
                     // The release is also a click: it must not toggle or extend the selection.
                     clicked = None;
+                    // The layer is the anchor of the next Shift-click's range.
+                    app.ui.layer_anchor = Some(row.id);
                 } else if !crate::menus::dev_mode_refuses(app, "object.rename") {
                     app.ui.rename = Some(Rename { id: row.id, start: true });
                 }