Detached placeholders follow each property's style precedence

Review follow-up (CodeRabbit on #1658):

- Text levels are resolved before the copy's style changes. A master
  placeholder's font reference reached the copy's text (body font in an
  accent colour for a title) although the original ignores it: text only
  takes the shape's or the layout placeholder's font reference.
- Fill, line and effects come from where `resolve::fill`, `resolve::line`
  and `resolve::effects` take them: the first shape in the chain with an
  explicit value or a style. A layout's (or the slide's own) style no
  longer loses to an explicit fill, line or effect on the master. The
  copy gets one style whose references each come from the shape that
  supplied that property; unused references are neutral.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/tests.rs

@@ -267,6 +267,106 @@ fn a_pasted_or_duplicated_placeholder_keeps_its_inherited_look() {
     assert!(s.doc().unwrap().doc.validate().is_empty());
 }
 
+/// The resolved fill, line and effects of shape `id` on the current slide, with their style colours.
+fn resolved_box(s: &Session, id: ShapeId) -> String {
+    use deckcraft_model::resolve;
+    let st = s.doc().unwrap();
+    let ctx = resolve::Ctx::for_slide(&st.doc, st.current_slide().unwrap()).unwrap();
+    let sh = st.shape(id).unwrap();
+    format!("{:?}\n{:?}\n{:?}", resolve::fill(&ctx, sh), resolve::line(&ctx, sh), resolve::effects(&ctx, sh))
+}
+
+/// Edit the title placeholders the current slide's title inherits from: its layout's and its
+/// master's. Returns the slide title's id.
+fn edit_title_parents(
+    s: &mut Session,
+    layout: impl FnOnce(&mut deckcraft_model::Shape),
+    master: impl FnOnce(&mut deckcraft_model::Shape),
+) -> ShapeId {
+    let st = s.doc_mut().unwrap();
+    let slide = st.current_slide().unwrap().clone();
+    let title = slide.shapes.iter().find(|x| x.ph_type().is_some_and(|k| k.is_title())).unwrap().id;
+    let doc = std::sync::Arc::make_mut(&mut st.doc);
+    let m = std::sync::Arc::make_mut(&mut doc.masters[0]);
+    let lay = m.layouts.iter_mut().find(|l| l.id == slide.layout).unwrap();
+    layout(lay.shapes.iter_mut().find(|x| x.ph_type().is_some_and(|k| k.is_title())).unwrap());
+    master(m.shapes.iter_mut().find(|x| x.ph_type().is_some_and(|k| k.is_title())).unwrap());
+    title
+}
+
+/// A copied placeholder takes each of fill, line and effects from where the original does: a
+/// style on the layout's placeholder (or on the slide's own) wins over an explicit value on the
+/// master's, as `resolve::fill`, `resolve::line` and `resolve::effects` decide.
+#[test]
+fn a_pasted_placeholder_keeps_the_style_precedence_of_its_box() {
+    use deckcraft_color::SchemeSlot;
+    use deckcraft_model::{ColorRef, Effects, Fill, Line, ShapeStyle};
+    for style_on_slide in [false, true] {
+        let mut s = session();
+        s.execute("slide.new", &json!({})).unwrap();
+        let style = ShapeStyle {
+            line_ref: (1, ColorRef::scheme(SchemeSlot::Accent2)),
+            fill_ref: (1, ColorRef::scheme(SchemeSlot::Accent1)),
+            effect_ref: (0, ColorRef::scheme(SchemeSlot::Accent3)),
+            font_ref: ("minor".into(), None),
+        };
+        let layout_style = (!style_on_slide).then(|| style.clone());
+        let title = edit_title_parents(
+            &mut s,
+            |l| l.style = layout_style,
+            |m| {
+                m.fill = Some(Fill::solid(ColorRef::scheme(SchemeSlot::Accent4)));
+                m.line = Some(Line::solid(ColorRef::scheme(SchemeSlot::Accent5), 20.0));
+                m.effects = Some(Effects { soft_edge: Some(5.0), ..Default::default() });
+            },
+        );
+        if style_on_slide {
+            s.edit(|doc, sel| {
+                let list = crate::shapes_mut(doc, sel).unwrap();
+                list.iter_mut().find(|x| x.id == title).unwrap().style = Some(style.clone());
+                Ok(())
+            })
+            .unwrap();
+        }
+        s.execute("text.set", &json!({"id": title.0, "text": "Styled title"})).unwrap();
+        let want = (resolved_box(&s, title), resolved_look(&s, title));
+        s.execute("selection.select", &json!({"id": title.0})).unwrap();
+        s.execute("edit.copy", &json!({})).unwrap();
+        s.execute("edit.paste", &json!({})).unwrap();
+        let copy = s.doc().unwrap().selection.shapes[0];
+        assert_eq!((resolved_box(&s, copy), resolved_look(&s, copy)), want, "style on the slide: {style_on_slide}");
+    }
+}
+
+/// The master's placeholder style never reaches the copy's text: the original's text ignores it
+/// (only the shape's or the layout's font reference counts), so the copy must too.
+#[test]
+fn a_pasted_placeholder_ignores_the_masters_font_reference() {
+    use deckcraft_color::SchemeSlot;
+    use deckcraft_model::{ColorRef, ShapeStyle};
+    let mut s = session();
+    s.execute("slide.new", &json!({})).unwrap();
+    let title = edit_title_parents(
+        &mut s,
+        |l| l.style = None,
+        |m| {
+            m.style = Some(ShapeStyle {
+                line_ref: (0, ColorRef::scheme(SchemeSlot::Accent2)),
+                fill_ref: (0, ColorRef::scheme(SchemeSlot::Accent1)),
+                effect_ref: (0, ColorRef::scheme(SchemeSlot::Accent3)),
+                font_ref: ("minor".into(), Some(ColorRef::scheme(SchemeSlot::Accent6))),
+            })
+        },
+    );
+    s.execute("text.set", &json!({"id": title.0, "text": "Title"})).unwrap();
+    let want = (resolved_box(&s, title), resolved_look(&s, title));
+    assert!(want.1.contains("+mj-lt"), "the title draws in the heading font: {}", want.1);
+    s.execute("selection.select", &json!({"id": title.0})).unwrap();
+    s.execute("edit.duplicate", &json!({})).unwrap();
+    let copy = s.doc().unwrap().selection.shapes[0];
+    assert_eq!((resolved_box(&s, copy), resolved_look(&s, copy)), want);
+}
+
 /// The same on every text placeholder of the sample deck (titles, bulleted bodies, subtitles).
 #[test]
 fn sample_placeholders_paste_with_their_look() {