Cover timeline right-click Pre-compose grouping the whole selection (#985, #1003)

Right-clicking selected layers and choosing Pre-compose grouped only the
right-clicked layer in 0.8.0 while Layer > Pre-compose grouped all of them.
The menu plumbing was fixed since; add a regression test driving the dialog
from both the outline row and the layer bar and asserting both selected
layers end up nested in the new composition.

crates/ui-egui/tests/ui_workflow_selection.rs

@@ -1,6 +1,6 @@
 //! User-reported selection, Project deletion, and render-queue drop regressions.
 use effectcraft_engine::{Session, project::LayerId};
-use effectcraft_ui_egui::{EffectcraftApp, dock::PanelKind};
+use effectcraft_ui_egui::{Dialog, EffectcraftApp, dock::PanelKind};
 use egui::{Event, Modifiers, PointerButton, Pos2, Rect, pos2, vec2};
 use egui_kittest::Harness;
 use egui_kittest::kittest::Queryable as _;
@@ -508,3 +508,44 @@ fn project_context_move_to_root_acts_on_the_whole_selection() {
         assert_eq!(project.item(effectcraft_engine::project::ItemId(*id)).unwrap().parent, None);
     }
 }
+
+/// Timeline right-click "Pre-compose…" groups every selected layer into one composition,
+/// like Layer > Pre-compose does, from both the outline row and the layer bar
+/// (#985, #1003).
+#[test]
+fn timeline_context_menu_precompose_groups_the_whole_selection() {
+    let right_click = |h: &mut Harness<'_, EffectcraftApp>, p: Pos2| {
+        for pressed in [true, false] {
+            h.input_mut().events.push(Event::PointerMoved(p));
+            h.input_mut().events.push(Event::PointerButton { pos: p, button: PointerButton::Secondary, pressed, modifiers: Modifiers::NONE });
+            h.step();
+        }
+        h.run_steps(3);
+    };
+    let row = |h: &Harness<'_, EffectcraftApp>, id: LayerId| {
+        let r = rect(h, &format!("timeline.layer.{}.row", id.0));
+        pos2(r.min.x + 210.0, r.center().y)
+    };
+    let bar = |h: &Harness<'_, EffectcraftApp>, id: LayerId| rect(h, &format!("timeline.layer.{}.bar", id.0)).center();
+    for via_bar in [false, true] {
+        let mut h = harness();
+        let ids: Vec<LayerId> = h.state().session.active_comp().unwrap().layers.iter().map(|l| l.id).collect();
+        let mut want: Vec<String> =
+            h.state().session.active_comp().unwrap().layers.iter().filter(|l| l.id == ids[0] || l.id == ids[1]).map(|l| l.name.clone()).collect();
+        want.sort();
+        h.state_mut().session.execute("layer.select", json!({"layers":[ids[0].0, ids[1].0]})).unwrap();
+        h.run_steps(3);
+        let p = if via_bar { bar(&h, ids[1]) } else { row(&h, ids[1]) };
+        right_click(&mut h, p);
+        h.get_by_label("Pre-compose…").click();
+        h.run_steps(3);
+        assert_eq!(h.state().dialog, Some(Dialog::Precompose), "via_bar={via_bar}: Pre-compose opens its dialog");
+        let ok = rect(&h, "dialog.precompose.ok").center();
+        click(&mut h, ok, Modifiers::NONE);
+        h.run_steps(3);
+        // The dialog opens the new composition holding both nested layers.
+        let mut nested: Vec<String> = h.state().session.active_comp().unwrap().layers.iter().map(|l| l.name.clone()).collect();
+        nested.sort();
+        assert_eq!(nested, want, "via_bar={via_bar}: both selected layers are nested");
+    }
+}