diff --git a/apps/ely-show/src/slideshow/start.rs b/apps/ely-show/src/slideshow/start.rs
index 855a587..d61ce44 100644
--- a/apps/ely-show/src/slideshow/start.rs
+++ b/apps/ely-show/src/slideshow/start.rs
@@ -141,7 +141,9 @@ impl Deck {
     /// Plays a copy from the first or shown slide.
     pub fn start_show(&mut self, here: bool, cx: &mut Context<Self>) {
         if self.show.is_some() || self.show_starting {
-            return log::info!("show: already playing or starting");
+            log::info!("show: already playing or starting");
+            let text = Deck::text(cx, "show.play.busy", &[]);
+            return self.toast(text, Severity::Warning, cx);
         }
         let Some(id) = self.core.active else {
             return;
@@ -180,7 +182,9 @@ impl Deck {
                 let Some(first) = first.filter(|_| deck.core.active == Some(id)) else {
                     discard(worker, doc, path, cx);
                     if deck.core.active != Some(id) {
-                        return log::info!("show: tab {id} is no longer shown");
+                        log::info!("show: tab {id} is no longer shown");
+                        let text = Deck::text(cx, "show.play.gone", &[]);
+                        return deck.toast(text, Severity::Warning, cx);
                     }
                     let text = Deck::text(cx, "show.play.none", &[]);
                     return deck.toast(text, Severity::Warning, cx);
@@ -214,6 +218,8 @@ impl Deck {
         let (Some(tab), Some(audience)) = (self.tab(starting.tab), displays.get(starting.audience))
         else {
             log::warn!("show: the tab or screen {} is gone", starting.audience);
+            let text = Deck::text(cx, "show.play.gone", &[]);
+            self.toast(text, Severity::Warning, cx);
             return discard(worker, starting.doc, starting.copy, cx);
         };
         let presenter = (displays.iter())
@@ -347,4 +353,45 @@ mod tests {
         };
         assert_eq!(super::bounds(area), want);
     }
+
+    #[test]
+    fn a_start_whose_screen_is_gone_says_so_and_drops_its_copy() {
+        use ely_office::prelude::*;
+        use gpui::AppContext as _;
+
+        use crate::tests::{settle, update};
+        let dir = tempfile::tempdir().expect("a temp dir");
+        let mut cx = gpui::TestAppContext::single();
+        let Some(deck) = crate::tests::deck(&mut cx, dir.path()) else {
+            eprintln!("SKIP: no LOK build");
+            return;
+        };
+        update(&mut cx, &deck, |deck, cx| deck.new_blank(cx));
+        settle(&cx, |app| deck.read(app).active_tab().is_some_and(|tab| !tab.extra.slides.list.is_empty()));
+        // The window's toasts live on its root.
+        let handle = cx.update(|app| deck.read(app).core.window).expect("a window");
+        let root = cx
+            .update_window(handle, |_, window, app| {
+                let root = ely_ui::document_root(ely_platform::AppId::Show, deck.clone().into(), &ely_ui::commands::FILE, Vec::new(), window, app);
+                deck.update(app, |deck, _| deck.core.root = root.downgrade());
+                root
+            })
+            .expect("the window lives");
+        let path = dir.path().join("copy.odp");
+        let starting = cx.update(|app| {
+            let deck = deck.read(app);
+            let tab = deck.active_tab().expect("a tab");
+            let mut worker = deck.core.worker.lock().expect("the worker lock");
+            let (_, doc, slides) = super::copy(&mut worker, &tab.doc, (&path, None)).expect("a copy");
+            super::Starting { tab: tab.id, slides, first: 0, doc, copy: path.clone(), audience: 99, presenter: false }
+        });
+        update(&mut cx, &deck, |deck, cx| {
+            deck.show_starting = true;
+            deck.open_show(starting, cx);
+        });
+        settle(&cx, |_| !path.exists());
+        let (toasts, gone) = cx.update(|app| (root.read(app).toasts(app), crate::deck::Deck::text(app, "show.play.gone", &[])));
+        assert!(toasts.iter().any(|(text, _)| *text == gone), "{toasts:?}");
+        assert!(cx.update(|app| !deck.read(app).show_starting && deck.read(app).show.is_none()));
+    }
 }
diff --git a/apps/ely-show/src/tests.rs b/apps/ely-show/src/tests.rs
index 05e3826..554db49 100644
--- a/apps/ely-show/src/tests.rs
+++ b/apps/ely-show/src/tests.rs
@@ -45,7 +45,7 @@ pub(super) fn deck(cx: &mut TestAppContext, dir: &Path) -> Option<Entity<Deck>>
 
 /// Steps the scheduler until `done` or ten seconds pass.
 #[track_caller]
-fn settle(cx: &TestAppContext, done: impl Fn(&gpui::App) -> bool) {
+pub(super) fn settle(cx: &TestAppContext, done: impl Fn(&gpui::App) -> bool) {
     let deadline = std::time::Instant::now() + std::time::Duration::from_secs(10);
     while std::time::Instant::now() < deadline {
         if !cx.executor().tick() {
@@ -59,7 +59,7 @@ fn settle(cx: &TestAppContext, done: impl Fn(&gpui::App) -> bool) {
     panic!("the state never settled");
 }
 
-fn update(
+pub(super) fn update(
     cx: &mut TestAppContext,
     deck: &Entity<Deck>,
     f: impl FnOnce(&mut Deck, &mut gpui::Context<Deck>),
diff --git a/apps/ely-show/src/tests/play.rs b/apps/ely-show/src/tests/play.rs
index 9697034..417812b 100644
--- a/apps/ely-show/src/tests/play.rs
+++ b/apps/ely-show/src/tests/play.rs
@@ -145,3 +145,56 @@ fn a_click_on_media_finds_it_and_elsewhere_does_not() {
     assert_eq!(cx.update(|app| show.read(app).media_at(centre)), Some(0));
     assert_eq!(cx.update(|app| show.read(app).media_at((0.01, 0.01))), None);
 }
+
+#[test]
+fn a_second_start_says_the_show_is_busy() {
+    let dir = tempfile::tempdir().expect("a temp dir");
+    let mut cx = TestAppContext::single();
+    let Some(deck) = blank(&mut cx, dir.path()) else {
+        eprintln!("SKIP: no LOK build");
+        return;
+    };
+    // The window's toasts live on its root.
+    let root = super::slides::in_window(&mut cx, &deck, |deck, window, cx| {
+        let this = cx.entity();
+        let root = ely_ui::document_root(ely_platform::AppId::Show, this.into(), &ely_ui::commands::FILE, Vec::new(), window, cx);
+        deck.core.root = root.downgrade();
+        root
+    });
+    update(&mut cx, &deck, |deck, cx| {
+        deck.show_starting = true;
+        deck.start_show(false, cx);
+    });
+    cx.run_until_parked();
+    let (toasts, busy) = cx.update(|app| (root.read(app).toasts(app), Deck::text(app, "show.play.busy", &[])));
+    assert!(toasts.iter().any(|(text, _)| *text == busy), "{toasts:?}");
+}
+
+#[test]
+fn a_start_left_for_another_tab_says_so() {
+    let dir = tempfile::tempdir().expect("a temp dir");
+    let mut cx = TestAppContext::single();
+    let Some(deck) = blank(&mut cx, dir.path()) else {
+        eprintln!("SKIP: no LOK build");
+        return;
+    };
+    let first = cx.update(|app| deck.read(app).core.active.expect("a tab"));
+    update(&mut cx, &deck, |deck, cx| deck.new_blank(cx));
+    settle(&cx, |app| deck.read(app).core.tabs.len() == 2 && deck.read(app).core.active != Some(first));
+    let second = cx.update(|app| deck.read(app).core.active.expect("a tab"));
+    let root = super::slides::in_window(&mut cx, &deck, |deck, window, cx| {
+        let this = cx.entity();
+        let root = ely_ui::document_root(ely_platform::AppId::Show, this.into(), &ely_ui::commands::FILE, Vec::new(), window, cx);
+        deck.core.root = root.downgrade();
+        root
+    });
+    update(&mut cx, &deck, |deck, cx| {
+        deck.core.active = Some(first);
+        deck.start_show(false, cx);
+        // Another tab comes forward while the copy is read.
+        deck.core.active = Some(second);
+    });
+    let gone = cx.update(|app| Deck::text(app, "show.play.gone", &[]));
+    settle(&cx, |app| root.read(app).toasts(app).iter().any(|(text, _)| *text == gone));
+    assert!(cx.update(|app| !deck.read(app).show_starting && deck.read(app).show.is_none()));
+}
diff --git a/crates/ely-ui/src/i18n/play.rs b/crates/ely-ui/src/i18n/play.rs
index 0e72c03..182aaa0 100644
--- a/crates/ely-ui/src/i18n/play.rs
+++ b/crates/ely-ui/src/i18n/play.rs
@@ -10,6 +10,8 @@ pub(super) const EN: &[(&str, &str)] = &[
     ("show.play.screen", "Screen {number} ({width} × {height})"),
     ("show.play.start", "Start"),
     ("show.play.none", "Every slide is hidden"),
+    ("show.play.busy", "The show is already starting or playing"),
+    ("show.play.gone", "The show did not start: its deck or screen changed"),
     ("show.play.back", "Previous"),
     ("show.play.next", "Next"),
     ("show.play.place", "Slide {number} of {count}"),
@@ -70,6 +72,8 @@ pub(super) const ZH_CN: &[(&str, &str)] = &[
     ("show.play.screen", "屏幕 {number}（{width} × {height}）"),
     ("show.play.start", "开始放映"),
     ("show.play.none", "所有幻灯片都已隐藏"),
+    ("show.play.busy", "放映已在开始或进行中"),
+    ("show.play.gone", "放映未开始：文稿或屏幕已变"),
     ("show.play.back", "上一步"),
     ("show.play.next", "下一步"),
     ("show.play.place", "第 {number} 张，共 {count} 张"),
diff --git a/tasks/BUGS.md b/tasks/BUGS.md
index 6f1bdd2..694a169 100644
--- a/tasks/BUGS.md
+++ b/tasks/BUGS.md
@@ -32,7 +32,7 @@
 - [x] S-07 母版视图下演示检查的行按幻灯片序号跳转 — 母版视图下点行提示先关母版，不跳；R1 PASS
 - [x] S-08 刚编辑过幻灯片就进备注栏键入，备注可能丢 — 发出的备注待读回确认，键入中读回只移基线不动草稿；R2 PASS
 - [x] S-09 改尺寸失败后 `size_asked` 一直留着 — 所要尺寸带输入序号，发送前先记、未入队即清，命令落地后的读回即清；R2 PASS
-- [ ] S-10 开始放映的两处拒绝无提示（规则 2）
+- [x] S-10 开始放映的两处拒绝无提示（规则 2） — 三处拒绝都提示（另含读回时已换标签）；R2 PASS
 - [x] P-01 文件系统的 `PermissionDenied` 被拼成不存在的文案键，应用崩溃 — worker 的拒绝改为自有错误类型 Refused；R1 测试不跨平台、不看提示；组件库 f834f55 加 Toaster::shown；R2 PASS
 - [x] P-02 每次编辑落地清掉全部图块与缩略图，页面空白、刚画的墨迹消失 — 图块随 R2.6；缩略图在编辑后留到重画；R1、R2 测试未证实际绘制；R3 PASS
 - [x] P-03 “编辑文字和图片”先命中图片对象再命中文字；一点抖动就移动了背景图 — 包住文字块的对象让位于文字，移动须过 3 个窗口像素；R1 漏掉同点的小图；R2 PASS
diff --git a/tasks/reviews/S-10-r1.md b/tasks/reviews/S-10-r1.md
new file mode 100644
index 0000000..6c8f8a5
--- /dev/null
+++ b/tasks/reviews/S-10-r1.md
@@ -0,0 +1,3 @@
+FAIL
+
+apps/ely-show/src/tests/play.rs:149：S-10 的 gone 拒绝路径缺少回归测试，新增用例只断言 show_starting 时的 busy toast。具体场景：放映副本读取期间切换标签，或选屏后原标签／观众屏消失再开始放映；这些路径分别经过 apps/ely-show/src/slideshow/start.rs:183 和 :218。验证：在独立副本中移除两处 show.play.gone toast，保留日志与 discard，原有 13 个放映测试仍全部通过；本轮补充的两个定向探针在当前实现上通过，移除 toast 后均因窗口根的提示列表为空而失败。修复方向：为上述两条拒绝路径补充回归测试，覆盖标签切换、标签消失与观众屏失效，断言窗口根出现 show.play.gone、启动状态解除且放映副本被清理。
diff --git a/tasks/reviews/S-10-r2.md b/tasks/reviews/S-10-r2.md
new file mode 100644
index 0000000..7ef22e9
--- /dev/null
+++ b/tasks/reviews/S-10-r2.md
@@ -0,0 +1 @@
+PASS