fix: Keep the loading card's Cancel button still; deterministic Cancel test (#686)

The loading card was centred on its height, so Cancel moved when the progress bar or the saved preview appeared, and a click could miss it. That's what made the Cancel test flaky on slow runners. The card is now anchored at its top, Cancel sits in the heading row and the progress bar is always shown. Progress::hold_at lets the test hold a load at a feature boundary until it's cancelled.

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

crates/ui-egui/src/file_load.rs

@@ -95,6 +95,9 @@ impl Running {
 pub struct FileLoad {
     queued: VecDeque<Request>,
     running: Option<Running>,
+    /// Tests: the next load waits before this feature until cancelled.
+    #[cfg(test)]
+    pub hold_at: Option<usize>,
 }
 
 impl FileLoad {
@@ -102,6 +105,10 @@ impl FileLoad {
     pub fn busy(&self) -> bool {
         self.running.as_ref().is_some_and(|r| !r.cancelled()) || !self.queued.is_empty()
     }
+    /// The running load's progress: (features rebuilt, timeline length).
+    pub fn features(&self) -> Option<(usize, usize)> {
+        self.running.as_ref().map(|r| r.progress.features())
+    }
     /// Nothing running or queued (a cancelled job may still be finishing in [`Self::busy`]'s eyes).
     pub fn idle(&self) -> bool {
         self.running.is_none() && self.queued.is_empty()
@@ -210,6 +217,10 @@ fn start(app: &mut SolveApp) {
     let phase = Arc::new(AtomicU8::new(0));
     let worker_phase = phase.clone();
     let progress = Arc::new(Progress::default());
+    #[cfg(test)]
+    if let Some(i) = app.file_load.hold_at.take() {
+        progress.hold_at(i);
+    }
     let worker_progress = progress.clone();
     let (tx, rx) = std::sync::mpsc::channel();
     let (preview_tx, preview_rx) = std::sync::mpsc::channel();
@@ -491,22 +502,32 @@ pub fn show(app: &mut SolveApp, ctx: &egui::Context) {
         ui.painter().rect_filled(cover, 0.0, egui::Color32::from_black_alpha(70));
     });
     let width = 340.0f32.min(cover.width() - 16.0).max(120.0);
-    egui::Area::new(card_id).order(egui::Order::Middle).pivot(egui::Align2::CENTER_CENTER).fixed_pos(centre).show(ctx, |child| {
+    // Anchored at its top with Cancel in the heading row: the card grows downwards (the saved
+    // preview, the progress bar) and Cancel never moves under the pointer.
+    let top = egui::pos2(centre.x, (centre.y - 120.0).max(cover.top() + 8.0));
+    egui::Area::new(card_id).order(egui::Order::Middle).pivot(egui::Align2::CENTER_TOP).fixed_pos(top).show(ctx, |child| {
         egui::Frame::popup(child.style()).fill(t.panel).show(child, |ui| {
             ui.set_width(width - 16.0);
-            ui.label(
-                egui::RichText::new(if cancelled {
-                    "Waiting for file operation"
-                } else {
-                    match r.request.kind {
-                        Kind::Insert => "Inserting geometry",
-                        Kind::Open => "Opening design",
-                        Kind::Recover { .. } => "Recovering design",
-                    }
-                })
-                .strong()
-                .size(14.0),
-            );
+            ui.horizontal(|ui| {
+                ui.label(
+                    egui::RichText::new(if cancelled {
+                        "Waiting for file operation"
+                    } else {
+                        match r.request.kind {
+                            Kind::Insert => "Inserting geometry",
+                            Kind::Open => "Opening design",
+                            Kind::Recover { .. } => "Recovering design",
+                        }
+                    })
+                    .strong()
+                    .size(14.0),
+                );
+                ui.with_layout(egui::Layout::right_to_left(egui::Align::Center), |ui| {
+                    let b = ui.button("Cancel");
+                    crate::scenario::publish_handle("file_loading:cancel", b.rect.center());
+                    cancel |= b.clicked();
+                });
+            });
             ui.label(egui::RichText::new(format!("{name}…")).weak());
             if let Some(preview) = r.preview.as_ref().filter(|_| !cancelled) {
                 let w = ui.available_width().min(320.0);
@@ -527,15 +548,15 @@ pub fn show(app: &mut SolveApp, ctx: &egui::Context) {
                     }
                 });
             });
-            if phase == 0 && total > 0 && !cancelled {
-                ui.add(egui::ProgressBar::new(done as f32 / total as f32).desired_height(6.0));
-            }
-            ui.add_space(4.0);
-            ui.allocate_ui_with_layout(egui::vec2(ui.available_width(), 24.0), egui::Layout::right_to_left(egui::Align::Center), |ui| {
-                let b = ui.button("Cancel");
-                crate::scenario::publish_handle("file_loading:cancel", b.rect.center());
-                cancel |= b.clicked();
-            });
+            // Always there, so the card keeps its height as the phases change.
+            let fraction = if cancelled || total == 0 {
+                0.0
+            } else if phase == 0 {
+                done as f32 / total as f32
+            } else {
+                1.0
+            };
+            ui.add(egui::ProgressBar::new(fraction).desired_height(6.0));
         });
     });
     if cancel && !cancelled {