Issue #8: prefer the integrated GPU, and the save prompt answers to the keyboard

- On hybrid-graphics laptops wgpu picked the discrete GPU (egui-wgpu defaults
  to HighPerformance). NVIDIA's can lose or corrupt its memory across suspend
  and screen lock, which matches the illegible window in #8. PrintCraft now
  asks for the low-power adapter unless WGPU_POWER_PREF is set; one-GPU
  machines are unaffected, and it saves battery.
- "Save changes?" had no keyboard: Enter saves, Escape cancels, and Don't save
  takes Cmd/Ctrl+D (macOS) or Alt+D / Alt+N (the mnemonics the reporter tried).
  Its keys are read before the canvas (which took Escape), and no other
  shortcut runs underneath it (Cmd+D opened Document properties).

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

apps/printcraft/src/main.rs

@@ -71,7 +71,8 @@ fn main() -> eframe::Result {
     }
     // eframe would otherwise derive the settings folder from the app id: keep it under "PrintCraft".
     let persistence_path = eframe::storage_dir("PrintCraft").map(|d| d.join("app.ron"));
-    let native = eframe::NativeOptions { viewport, persistence_path, ..Default::default() };
+    let mut native = eframe::NativeOptions { viewport, persistence_path, ..Default::default() };
+    prefer_integrated_gpu(&mut native);
     eframe::run_native(
         "PrintCraft",
         native,
@@ -125,3 +126,16 @@ fn write_control_file(path: &str, port: u16, token: &str) -> std::io::Result<()>
     }
     f.write_all(json.as_bytes())
 }
+
+/// Draw on the integrated GPU unless `WGPU_POWER_PREF` says otherwise. A PDF viewer has no use
+/// for a discrete GPU, and on hybrid-graphics laptops (NVIDIA Optimus) the discrete one can lose
+/// or corrupt its memory across suspend and screen lock, leaving the window illegible (issue #8).
+/// It also saves battery. Machines with one GPU are unaffected.
+fn prefer_integrated_gpu(native: &mut eframe::NativeOptions) {
+    if std::env::var_os("WGPU_POWER_PREF").is_some() {
+        return;
+    }
+    if let eframe::egui_wgpu::WgpuSetup::CreateNew(setup) = &mut native.wgpu_options.wgpu_setup {
+        setup.power_preference = eframe::wgpu::PowerPreference::LowPower;
+    }
+}

crates/ui-egui/src/dialogs.rs

@@ -1252,6 +1252,24 @@ fn draft_changes(app: &PrintCraftApp) -> Option<Vec<Edit>> {
     Some(edits)
 }
 
+/// The "Save changes?" prompt's keys (issue #8), read before anything else can take them: Enter
+/// saves (the default button) and Escape cancels; Don't save takes ⌘D / Ctrl+D, the macOS
+/// convention, or Alt+D / Alt+N, the mnemonics Windows and Linux desktops use for it.
+pub(crate) fn save_prompt_key(ctx: &egui::Context) -> Option<Option<bool>> {
+    use egui::{Key, Modifiers};
+    ctx.input_mut(|i| {
+        if i.consume_key(Modifiers::NONE, Key::Enter) {
+            Some(Some(true))
+        } else if i.consume_key(Modifiers::NONE, Key::Escape) {
+            Some(None)
+        } else if [(Modifiers::COMMAND, Key::D), (Modifiers::ALT, Key::D), (Modifiers::ALT, Key::N)].into_iter().any(|(m, k)| i.consume_key(m, k)) {
+            Some(Some(false))
+        } else {
+            None
+        }
+    })
+}
+
 /// "Save changes?" when closing a tab or quitting with unsaved edits.
 fn save_prompt(app: &mut PrintCraftApp, ctx: &egui::Context) {
     let Some(req) = app.close_request else { return };

crates/ui-egui/src/lib.rs

@@ -1061,6 +1061,15 @@ impl PrintCraftApp {
 
     fn shortcuts(&mut self, ctx: &egui::Context) {
         use egui::Key;
+        // "Save changes?" is modal: its keys are its own (⌘D is Don't save there, not Document
+        // properties; Escape cancels it rather than clearing a selection), and nothing may run
+        // underneath it. They are read here, before the canvas can consume them.
+        if self.close_request.is_some() {
+            if let Some(choice) = dialogs::save_prompt_key(ctx) {
+                self.resolve_close(ctx, choice);
+            }
+            return;
+        }
         self.registry_shortcuts(ctx);
         if self.full_screen && ctx.input(|i| i.key_pressed(Key::Escape)) {
             self.set_full_screen(ctx, false);

crates/ui-egui/tests/editing.rs

@@ -212,6 +212,44 @@ fn closing_a_dirty_tab_can_save_first() {
     let _ = std::fs::remove_file(out);
 }
 
+#[test]
+fn the_save_prompt_answers_to_the_keyboard() {
+    // Issue #8: Enter saves; ⌘D / Ctrl+D, Alt+D and Alt+N don't save; Escape cancels. While the
+    // prompt is open, ⌘D is not Document properties.
+    for (m, key) in [(Modifiers::COMMAND, Key::D), (Modifiers::ALT, Key::D), (Modifiers::ALT, Key::N)] {
+        let mut h = organize(2);
+        h.get_by_label("Rotate clockwise").click();
+        h.run_steps(3);
+        h.key_press_modifiers(Modifiers::COMMAND, Key::W);
+        h.run_steps(3);
+        h.get_by_label_contains("Save changes to “doc.pdf”");
+        h.key_press_modifiers(m, key);
+        h.run_steps(3);
+        assert!(h.state().views.is_empty(), "{m:?}+{key:?} doesn't save and closes");
+        assert!(h.state().dialog.is_none(), "{m:?}+{key:?} ran no command underneath");
+    }
+    let mut h = organize(2);
+    h.get_by_label("Rotate clockwise").click();
+    h.run_steps(3);
+    h.key_press_modifiers(Modifiers::COMMAND, Key::W);
+    h.run_steps(3);
+    h.key_press(Key::Escape);
+    h.run_steps(3);
+    assert_eq!(h.state().views.len(), 1, "Escape cancels");
+    assert!(h.state().close_request.is_none());
+
+    let out = temp_path("enter-saves.pdf");
+    h.state_mut().save_override = Some(out.to_string_lossy().into_owned());
+    h.key_press_modifiers(Modifiers::COMMAND, Key::W);
+    h.run_steps(3);
+    h.key_press(Key::Enter);
+    h.run_steps(3);
+    assert!(h.state().views.is_empty(), "Enter saves and closes");
+    let saved = printcraft_render::inspect(std::sync::Arc::new(std::fs::read(&out).unwrap()), None).unwrap();
+    assert_eq!(saved.pages[0].rotation, 90);
+    let _ = std::fs::remove_file(out);
+}
+
 #[test]
 fn clean_tabs_close_without_asking() {
     let mut h = harness(1, |_| {});