UI: "Preparing the GPU compositor…" stays until the compositor is attached

The status line is the toast that clears itself after 5 s, so the
preparing notice went blank while the viewer was still on the CPU for the
rest of a cold-cache build (tens of seconds), though `init_gpu` says the
status bar tells the user so. draw_toast now leaves that one status up
while `gpu_initializing()`; `finish_gpu_build` clears it when the
compositor lands, and the worker's repaint brings that frame, so the
toast doesn't tick meanwhile. A click still dismisses it; every other
status clears as before.

Test: with the build held on its gate, 30 more steps (7.5 s) leave the
status as it was; before this change it was empty by then.

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

crates/ui-egui/src/app/frame.rs

@@ -461,6 +461,13 @@ impl EffectcraftApp {
                 self.ui.status.clear();
                 self.toast = None;
             }
+            // "Preparing the GPU compositor…" stays until the compositor is attached (tens of
+            // seconds on a cold shader cache), not 5 s: `finish_gpu_build` clears it, and the
+            // worker's repaint brings that frame, so nothing needs to tick meanwhile. A click
+            // still dismisses it.
+            if self.ui.status == crate::GPU_PREPARING && self.gpu_initializing() {
+                return;
+            }
             ui.ctx().request_repaint_after(std::time::Duration::from_millis(500));
             if !self.ui.status.is_empty() {
                 let since: f64 = ui.data(|d| d.get_temp(egui::Id::unique("status-since")).unwrap_or(now));

crates/ui-egui/tests/it/ui_gpu.rs

@@ -47,6 +47,9 @@ fn the_interface_draws_and_composites_on_the_cpu_while_the_gpu_compositor_is_bui
     let s = small_session();
     let mut h = Harness::builder().with_size(egui::vec2(1200.0, 800.0)).wgpu().build_eframe(move |_| {
         let mut app = EffectcraftApp::new(s);
+        // The status line's 5 s expiry reads the app clock: a manual one makes the steps below
+        // stand for a known span of time.
+        app.use_manual_clock();
         app.hooks.before_gpu_build = Some(Box::new(move || {
             let _ = gate.recv();
         }));
@@ -67,6 +70,14 @@ fn the_interface_draws_and_composites_on_the_cpu_while_the_gpu_compositor_is_bui
     assert_eq!(h.state().session.accel_note.as_deref(), Some(effectcraft_ui_egui::GPU_PREPARING));
     assert!(h.state().frames.last_ms.lock().map(|v| *v > 0.0).unwrap_or(false), "a frame was composited on the CPU meanwhile");
     assert!(h.state_mut().viewer_pixels().is_some(), "the viewer shows that frame");
+    // Other statuses clear after 5 s; this one stays for as long as the build takes (each step
+    // is a quarter of a second).
+    for _ in 0..30 {
+        h.state_mut().clock_mut().advance(0.25);
+        h.step();
+    }
+    assert!(h.state().gpu_initializing());
+    assert_eq!(h.state().ui.status, effectcraft_ui_egui::GPU_PREPARING, "the status line still says so 7.5 s later");
     release.send(()).unwrap();
     settle(&mut h);
     assert!(!h.state().gpu_initializing());