[JJ3] show.presenter answers {on, window}

The answer was null. Presenter view is its own window beside the show window,
so window is true; the doc says where it appears.

PowerPoint: Presenter View opens in a separate window on the second display
when the show starts (the Use Presenter View option); same here.

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

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

@@ -162,7 +162,11 @@ impl SlideApp {
                     self.start_show(from, false);
                 }
             }
-            "show.presenter" => self.ui.presenter_view = self.flag(p, self.ui.presenter_view),
+            "show.presenter" => {
+                self.ui.presenter_view = self.flag(p, self.ui.presenter_view);
+                // The browser build has one viewport: presenter view is drawn inside the page.
+                return Ok(json!({"on": self.ui.presenter_view, "window": !cfg!(target_arch = "wasm32")}));
+            }
             "show.end" => {
                 self.show = None;
                 self.media.stop_owned(media::Owner::Show);

crates/ui-egui/src/lib.rs

@@ -109,7 +109,12 @@ pub const UI_COMMANDS: &[(&str, &str, Option<&str>, &str)] = &[
     ("view.grayscale", "Grayscale", None, "{on?: bool}"),
     ("view.newWindow", "New Window", None, "{on?: bool, slide?: index, delta?: int}"),
     ("show.start", "Slide Show", Some("F5"), "{from?: index, custom?: name}"),
-    ("show.presenter", "Presenter View", None, "{on?: bool}"),
+    (
+        "show.presenter",
+        "Presenter View",
+        None,
+        "{on?: bool} → {on, window} (presenter view, with notes, a clock and the next slide, appears in its own separate window beside the show window when the show starts; window is false in the browser build, which draws it inside the page)",
+    ),
     ("show.end", "End Show", None, "{}"),
     ("animation.preview", "Preview Animations", None, "{on?: bool, from?: effect index}"),
     ("app.home", "Home", None, "{on?}"),
@@ -445,6 +450,8 @@ mod ime_tests;
 #[cfg(test)]
 mod last_color_tests;
 #[cfg(test)]
+mod presenter_tests;
+#[cfg(test)]
 mod replacefonts_tests;
 #[cfg(test)]
 mod reuse_picker_tests;

crates/ui-egui/src/presenter_tests.rs

@@ -0,0 +1,18 @@
+//! JJ3: `show.presenter` answers the setting and where presenter view appears.
+#![allow(clippy::unwrap_used, clippy::expect_used)]
+
+use serde_json::json;
+
+use crate::{Services, SlideApp};
+use deckcraft_engine::Session;
+
+#[test]
+fn show_presenter_answers_on_and_window() {
+    let mut app = SlideApp::new(Session::with_new(), Services::default());
+    let v = app.run("show.presenter", json!({"on": true})).unwrap();
+    assert_eq!(v, json!({"on": true, "window": true}));
+    let v = app.run("show.presenter", json!({})).unwrap();
+    assert_eq!(v["on"], false, "no `on` toggles: {v}");
+    let doc = crate::UI_COMMANDS.iter().find(|c| c.0 == "show.presenter").unwrap().3;
+    assert!(doc.contains("separate window"), "{doc}");
+}