fix(ui): show error toasts raised by a slow frame for their full 3 s

A toast's clock started from the time of the frame that first drew it. That
time is taken when the frame starts, before whatever raised the toast ran:
the Open dialog and a failed open blocked that frame for longer than 3 s, so
the error expired before it was ever seen and the open failed silently. The
clock now starts on the frame after the first one that draws the toast.

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

crates/ui-egui/src/idle_tests.rs

@@ -190,6 +190,25 @@ fn a_toast_wakes_the_ui_only_to_go_away() {
     assert!(h.app.ui.toast.is_none(), "gone after 3 s");
 }
 
+#[test]
+fn a_toast_raised_by_a_slow_frame_still_shows_for_3_s() {
+    let (mut h, _) = document();
+    h.settle();
+    // The Open dialog and a failed open block the frame that raises the error: the next frame
+    // comes 5 s after it started.
+    h.app.toast("can't open file.fig");
+    h.frame(vec![]);
+    h.time += 5.0;
+    h.frame(vec![]);
+    assert!(h.app.ui.toast.is_some(), "shown, not expired by the wait");
+    h.time += 2.0;
+    h.frame(vec![]);
+    assert!(h.app.ui.toast.is_some());
+    h.time += 1.5;
+    h.frame(vec![]);
+    assert!(h.app.ui.toast.is_none(), "gone after 3 s");
+}
+
 #[test]
 fn a_finished_background_render_wakes_the_ui() {
     let ctx = egui::Context::default();

crates/ui-egui/src/lib.rs

@@ -274,6 +274,17 @@ pub const AUTOSAVE_SECS: f64 = 30.0 * 60.0;
 /// How long a toast shows (seconds).
 const TOAST_SECS: f64 = 3.0;
 
+/// How long a toast has been showing ([`UiState::toast`]).
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum ToastClock {
+    /// Raised, not drawn yet.
+    Raised,
+    /// Drawn once; the next frame starts the clock.
+    Drawn,
+    /// Showing since this time (UI clock, seconds).
+    Since(f64),
+}
+
 /// Draw another frame `secs` from now (nothing else needs drawing until then: an idle window draws
 /// no frames).
 #[track_caller]
@@ -337,8 +348,8 @@ pub struct UiState {
     pub title_bar: TitleBar,
     /// Every icon on one screen, for reviewing the set (control channel `ui.set {iconGallery}`).
     pub icon_gallery: bool,
-    /// A message at the bottom of the window and when it first showed (UI clock, seconds).
-    pub toast: Option<(String, Option<f64>)>,
+    /// A message at the bottom of the window and how long it has been showing.
+    pub toast: Option<(String, ToastClock)>,
     pub present: Option<present::Presenter>,
     /// The full-window presenter's options (how it sizes the prototype), kept between
     /// presentations.
@@ -648,7 +659,7 @@ impl FigApp {
     }
 
     pub fn toast(&mut self, msg: impl Into<String>) {
-        self.ui.toast = Some((msg.into(), None));
+        self.ui.toast = Some((msg.into(), ToastClock::Raised));
     }
 
     /// Say that `n` documents left unsaved by a crash were opened again from recovery copies.
@@ -1135,16 +1146,32 @@ impl FigApp {
     }
 
     fn toast_ui(&mut self, ctx: &egui::Context) {
-        let Some((msg, shown)) = &mut self.ui.toast else { return };
+        let Some((msg, clock)) = &mut self.ui.toast else { return };
         let now = ctx.input(|i| i.time);
-        let left = TOAST_SECS - (now - *shown.get_or_insert(now));
+        // The clock starts on the frame after the one that first draws the toast: that frame's
+        // time was taken before whatever raised it ran (a file dialog, a long open), and would
+        // count that wait against it, so a failed open's message expired before it was seen.
+        let left = match *clock {
+            ToastClock::Raised => {
+                *clock = ToastClock::Drawn;
+                ctx.request_repaint();
+                TOAST_SECS
+            }
+            ToastClock::Drawn => {
+                *clock = ToastClock::Since(now);
+                TOAST_SECS
+            }
+            ToastClock::Since(t) => TOAST_SECS - (now - t),
+        };
         if left <= 0.0 {
             self.ui.toast = None;
             return;
         }
         let msg = msg.clone();
         // Nothing moves while it shows: the next frame it needs is the one that hides it.
-        repaint_in(ctx, left);
+        if matches!(clock, ToastClock::Since(_)) {
+            repaint_in(ctx, left);
+        }
         let screen = ctx.content_rect();
         egui::Area::new(egui::Id::new("toast"))
             .fixed_pos(egui::pos2(screen.center().x, screen.max.y - 96.0))