M13.6: variable font axes in the character style

CharStyle/TextDoc variations (layer.setText variations), shaped with harfrust instances so
advances follow HVAR/gvar, outlines drawn at the design-space position, animator deltas relative
to the style's values, Character panel Variable Font Axes fields (character.axis.<tag>).

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

crates/engine/src/commands/layer.rs

@@ -1163,7 +1163,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "Edit Text",
             [],
             None,
-            "{layer?, range?: [start, end] (characters; default all), text?, font?, style?, size?, fill?, stroke?, applyFill?, applyStroke?, strokeWidth?, tracking?, leading?: px|\"auto\", baselineShift? px, hScale? %, vScale? %, tsume? %, fauxBold?, fauxItalic?, allCaps?, smallCaps?, baseline?: normal|superscript|subscript, superscript?, subscript?, kerning?: metrics|optical|number, ligatures?, OpenType: discretionaryLigatures?, contextualAlternates?, stylisticAlternates?, stylisticSets?: [1–20], ss01…ss20?, swash?, titling?, ordinals?, fractions?, allSmallCaps?, figureStyle?: default|lining|oldStyle, figureWidth?: default|proportional|tabular, figures?, justify?: left|center|right|justifyLeft|justifyCenter|justifyRight|justifyAll, indentLeft?, indentRight?, indentFirst?, spaceBefore?, spaceAfter?, direction?: ltr|rtl, composer?: everyLine|singleLine, hangingPunctuation?, strokeOverFill?, box?: [x,y,w,h]|null (layer space), vertical?}",
+            "{layer?, range?: [start, end] (characters; default all), text?, font?, style?, size?, fill?, stroke?, applyFill?, applyStroke?, strokeWidth?, tracking?, leading?: px|\"auto\", baselineShift? px, hScale? %, vScale? %, tsume? %, fauxBold?, fauxItalic?, allCaps?, smallCaps?, baseline?: normal|superscript|subscript, superscript?, subscript?, kerning?: metrics|optical|number, ligatures?, OpenType: discretionaryLigatures?, contextualAlternates?, stylisticAlternates?, stylisticSets?: [1–20], ss01…ss20?, swash?, titling?, ordinals?, fractions?, allSmallCaps?, figureStyle?: default|lining|oldStyle, figureWidth?: default|proportional|tabular, figures?, variations?: {tag: value} (variable font axes; null resets), justify?: left|center|right|justifyLeft|justifyCenter|justifyRight|justifyAll, indentLeft?, indentRight?, indentFirst?, spaceBefore?, spaceAfter?, direction?: ltr|rtl, composer?: everyLine|singleLine, hangingPunctuation?, strokeOverFill?, box?: [x,y,w,h]|null (layer space), vertical?}",
             has_layers,
             set_text
         ),

crates/engine/src/tests_tail.rs

@@ -326,6 +326,51 @@ fn variable_font_axes_animator() {
     let _ = info;
 }
 
+#[test]
+fn variable_font_axes_in_the_character_style() {
+    let mut s = comp(600, 200);
+    let t = s.execute("layer.newText", json!({"text": "Hamburg", "size": 60})).unwrap()["layer"].as_u64().unwrap();
+    // The attribute round-trips and is undoable even for static fonts (it is kept, unused).
+    s.execute("layer.setText", json!({"layer": t, "variations": {"wght": 650}})).unwrap();
+    let d = crate::commands::text_edit::layer_doc(&s, LayerId(t)).unwrap();
+    assert_eq!(d.style_at(0).variations, vec![("wght".to_string(), 650.0)]);
+    assert_eq!(effectcraft_keyframe::text_doc::char_style_json(&d.style_at(0))["variations"], json!({"wght": 650.0}));
+    s.execute("layer.setText", json!({"layer": t, "range": [0, 3], "variations": {"wght": null}})).unwrap();
+    let d = crate::commands::text_edit::layer_doc(&s, LayerId(t)).unwrap();
+    assert!(d.style_at(0).variations.is_empty() && !d.style_at(5).variations.is_empty());
+    s.execute("edit.undo", json!({})).unwrap();
+    s.execute("edit.undo", json!({})).unwrap();
+    assert!(crate::commands::text_edit::layer_doc(&s, LayerId(t)).unwrap().style_at(0).variations.is_empty());
+    assert!(s.execute("layer.setText", json!({"layer": t, "variations": 3})).is_err());
+    let Some((face, axes)) = effectcraft_text::variable::find_variable_face() else {
+        eprintln!("no variable font installed: rendering check skipped");
+        return;
+    };
+    let info = effectcraft_text::fonts::face(face).info.clone();
+    if effectcraft_text::resolve(&info.family, &info.style).face != face {
+        eprintln!("variable face not reachable by family/style: skipped");
+        return;
+    }
+    s.execute("layer.setText", json!({"layer": t, "font": info.family, "style": info.style})).unwrap();
+    let a = axes.iter().find(|a| a.tag == "wght" && a.max > a.min).or_else(|| axes.iter().find(|a| a.max > a.min)).unwrap().clone();
+    let geom = |s: &Session| {
+        let cid = s.active_comp_id().unwrap();
+        let comp = s.project.comp(cid).unwrap();
+        let ctx = effectcraft_render::EvalCtx::new(&s.project, cid, comp, s.time());
+        let l = comp.layer(LayerId(t)).unwrap();
+        let paths = effectcraft_render::text::glyph_paths(&ctx, l);
+        let area: f64 = paths.iter().map(|(p, _)| effectcraft_text::kurbo::Shape::area(p).abs()).sum();
+        let right = paths.iter().map(|(p, _)| effectcraft_text::kurbo::Shape::bounding_box(p).x1).fold(f64::MIN, f64::max);
+        (area, right)
+    };
+    s.execute("layer.setText", json!({"layer": t, "variations": {a.tag.trim_end(): a.min}})).unwrap();
+    let lo = geom(&s);
+    s.execute("layer.setText", json!({"layer": t, "variations": {a.tag.trim_end(): a.max}})).unwrap();
+    let hi = geom(&s);
+    assert!((hi.0 - lo.0).abs() > 1.0, "{} outlines {lo:?} → {hi:?}", a.tag);
+    assert!((hi.1 - lo.1).abs() > 0.5, "{} advances {lo:?} → {hi:?}", a.tag);
+}
+
 #[test]
 fn camera_focus_commands_undo_and_serde() {
     let mut s = comp(400, 300);