Part of #673: a document tab's close box sits where the platform puts it

Document tabs drew their close box before the title on every platform, the
macOS convention. On Windows, Linux and the web it now comes after the title,
as those platforms' tabs (and Adobe's own apps there) put it; macOS keeps it
before.

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

crates/ui-egui/src/chrome.rs

@@ -319,6 +319,10 @@ fn tab_title(d: &vectorcraft_engine::DocState, zoom: f64, outline: bool) -> Stri
     format!("{}{} @ {} ({mode})", d.title(), if d.is_dirty() { "*" } else { "" }, zoom_label(zoom).replace('%', " %"))
 }
 
+/// Whether a document tab's × comes before its title (macOS) rather than after it (Windows,
+/// Linux and the web).
+const CLOSE_BEFORE_TITLE: bool = cfg!(target_os = "macos");
+
 /// Document tab strip: "Name* @ 66.67% (RGB/Preview)". User Interface › Large Tabs makes the tabs
 /// taller, with larger titles.
 pub fn doc_tabs(app: &mut VectorcraftApp, ui: &mut Ui) {
@@ -346,11 +350,13 @@ pub fn doc_tabs(app: &mut VectorcraftApp, ui: &mut Ui) {
             ui.painter().rect_filled(r, 0.0, t.hover.gamma_multiply(0.4));
         }
         ui.painter().line_segment([r.right_top(), r.right_bottom()], Stroke::new(1.5, t.border));
-        // × at the left like Illustrator.
-        let xr = egui::Rect::from_center_size(egui::pos2(r.left() + 16.0, r.center().y), vec2(12.0, 12.0));
+        // The × where each platform puts a tab's: before the title on macOS, after it elsewhere
+        // (#673).
+        let (x_center, title_left) = if CLOSE_BEFORE_TITLE { (r.left() + 16.0, r.left() + 32.0) } else { (r.right() - 16.0, r.left() + 14.0) };
+        let xr = egui::Rect::from_center_size(egui::pos2(x_center, r.center().y), vec2(12.0, 12.0));
         let xresp = ui.interact(xr.expand(3.0), ui.id().with(("tabx", i)), Sense::click());
         icons::paint(ui, "x", xr, if xresp.hovered() { t.text_strong } else { t.text });
-        ui.painter().galley(egui::pos2(r.left() + 32.0, r.center().y - galley.size().y / 2.0), galley, t.text);
+        ui.painter().galley(egui::pos2(title_left, r.center().y - galley.size().y / 2.0), galley, t.text);
         if xresp.clicked() {
             close = Some(i);
         } else if resp.clicked() {
@@ -782,6 +788,44 @@ mod tests {
         }
     }
 
+    /// A document tab's × sits where the platform puts it (#673): after the title on Windows,
+    /// Linux and the web, before it on macOS; clicking it closes that document.
+    #[test]
+    fn a_tabs_close_box_sits_where_the_platform_puts_it() {
+        let mut app = crate::VectorcraftApp::new(Session::new(), Default::default());
+        app.session.execute("file.new", &json!({"width": 100, "height": 100})).unwrap();
+        app.session.execute("file.new", &json!({"width": 100, "height": 100})).unwrap();
+        let ctx = egui::Context::default();
+        crate::theme::install_fonts(&ctx);
+        let screen = egui::Rect::from_min_size(egui::Pos2::ZERO, egui::vec2(1200.0, 200.0));
+        let frame = |app: &mut crate::VectorcraftApp, events: Vec<egui::Event>| {
+            let mut out = ctx.run_ui(egui::RawInput { screen_rect: Some(screen), events, ..Default::default() }, |ui| super::doc_tabs(app, ui));
+            out.textures_delta.clear();
+            let mut titles = vec![];
+            for c in &out.shapes {
+                // The titles, not the × icons.
+                if let egui::Shape::Text(t) = &c.shape
+                    && t.visual_bounding_rect().width() > 30.0
+                {
+                    titles.push(t.visual_bounding_rect());
+                }
+            }
+            titles.sort_by(|a, b| a.left().total_cmp(&b.left()));
+            titles
+        };
+        let titles = frame(&mut app, vec![]);
+        assert_eq!(titles.len(), 2, "{titles:?}");
+        // The first tab's ×: 20 pt past its title's end, or 16 pt before its start.
+        let first = titles[0];
+        let x = if super::CLOSE_BEFORE_TITLE { first.left() - 16.0 } else { first.right() + 20.0 };
+        let at = egui::pos2(x, first.center().y);
+        let press = |pressed| egui::Event::PointerButton { pos: at, button: egui::PointerButton::Primary, pressed, modifiers: Default::default() };
+        frame(&mut app, vec![egui::Event::PointerMoved(at), press(true)]);
+        frame(&mut app, vec![press(false)]);
+        assert_eq!(app.session.documents().len(), 1, "the × closed the first document");
+        assert!(super::CLOSE_BEFORE_TITLE == cfg!(target_os = "macos"));
+    }
+
     /// One headless frame of the status bar; returns the artboard navigator's buttons, left to
     /// right: first, previous, next, last.
     fn navigator(app: &mut crate::VectorcraftApp, ctx: &egui::Context, events: Vec<egui::Event>) -> Vec<egui::Rect> {