diff --git a/apps/quickdeck/README.md b/apps/quickdeck/README.md
index 00cbd734..f40223b4 100644
--- a/apps/quickdeck/README.md
+++ b/apps/quickdeck/README.md
@@ -52,7 +52,7 @@ inspector opens over the canvas from an Inspector button in the toolbar
 | Editor | The navigator, the canvas and the inspector. Tap to choose (`deck.hit`), a long press adds to the choice, tap a chosen text box again (or double-tap) to type in it, drag to move, a handle to resize or rotate. Insert strips for text, pictures (from images/ or this device), shapes (the engine's gallery), tables and charts. A chosen video or sound plays from its control | `deck.slides`, `deck.slide`, `deck.view`, `deck.hit`, `deck.set_text`, `deck.format_state`, `deck.format`, `deck.insert`, `deck.shape`, `deck.picture`, `deck.table`, `deck.chart`, `deck.layouts`, `deck.slides_op`, `deck.design`, `deck.transition`, `deck.notes`, `deck.fonts`, `deck.shapes`, `deck.media` |
 | Sorter | Every slide as a tile in its sections, with its number and transition: choose slides, New slide, Duplicate, Delete, Hide or Show, Move earlier and later, drag a tile to move it, add, rename and remove sections | `deck.slides_op`, `deck.view` |
 | New from an outline | A card per slide (a title, then its points, one per line), a theme and a slide size, Make deck. Draft with AI asks the person's own provider for the cards (`model.complete`, fast class); without a provider it says to set one up in Settings → AI providers, and typing the outline works either way | `deck.create`; the host's `model.complete` |
-| Present | The slide alone on a dark stage inside the app's window, a small bar (previous, "4 / 12", next, Notes, the time, Exit) and an Exit in the corner; each build step shows its end state, and nothing animates. Notes opens a strip with the slide's notes. A clip set to play by itself starts when its slide shows, a tap on a clip plays or pauses it, and another slide or Exit stops it | `deck.show`, `deck.view {step}`, `deck.slide`, `deck.media` |
+| Present | The slide alone on a dark stage that takes the whole screen: the Present tap asks the shell to put the window in full screen (`window.fullscreen`), and where the host can't (card-host, a phone), the stage fills the app's window. A small bar (previous, "4 / 12", next, Notes, the time, Exit) and an Exit in the corner; Esc, the shell's key in full screen, also ends the show, and the window comes back as it was. Each build step shows its end state, and nothing animates; a slide drawn for the smaller window is drawn again for the full screen. Notes opens a strip with the slide's notes. A clip set to play by itself starts when its slide shows, a tap on a clip plays or pauses it, and another slide or Exit stops it | `deck.show`, `deck.view {step}`, `deck.slide`, `deck.media`; the shell's `window.fullscreen` |
 | Export | Presentation (.pptx), PDF (slides, notes pages or handouts, 1 to 9 per page) or Images (one PNG a slide); all slides, the current one or a range; hidden slides in or out; a name. The deck's earlier exports are listed and can be removed | `deck.export` |
 
 Undo and Redo use the engine's history; Save writes the native `.deckcraft`
diff --git a/apps/quickdeck/README.zh-CN.md b/apps/quickdeck/README.zh-CN.md
index 99929d5f..c5594f73 100644
--- a/apps/quickdeck/README.zh-CN.md
+++ b/apps/quickdeck/README.zh-CN.md
@@ -29,7 +29,7 @@ Quick Deck（`os.quickdeck`）是 OctoSense 桌面版的演示文稿应用：演
 | 编辑器 | 导航栏、画布和检查器。点按选中（`deck.hit`），长按加入或移出选择，再点一次已选中的文本框（或双击）即可在其中输入，拖动可移动，拖动控制点可调整大小或旋转。插入条用于文本、图片（来自 images/ 或本设备）、形状（引擎的形状库）、表格和图表。选中的视频或音频可用它的控件播放 | `deck.slides`、`deck.slide`、`deck.view`、`deck.hit`、`deck.set_text`、`deck.format_state`、`deck.format`、`deck.insert`、`deck.shape`、`deck.picture`、`deck.table`、`deck.chart`、`deck.layouts`、`deck.slides_op`、`deck.design`、`deck.transition`、`deck.notes`、`deck.fonts`、`deck.shapes`、`deck.media` |
 | 浏览视图 | 每张幻灯片以磁贴显示在所属分节中，带编号和切换效果：选择幻灯片、New slide、Duplicate、Delete、Hide 或 Show、前移和后移、拖动磁贴移动，添加、重命名和删除分节 | `deck.slides_op`、`deck.view` |
 | 从大纲新建 | 每张幻灯片一张卡片（一个标题，下面每行一个要点）、一个主题和一种幻灯片尺寸，然后 Make deck。Draft with AI 请用户自己的提供方起草卡片（`model.complete`，fast 档）；没有提供方时提示到 Settings → AI providers 设置，手动输入大纲始终可用 | `deck.create`；宿主的 `model.complete` |
-| 放映 | 幻灯片单独显示在应用窗口内的深色舞台上，下方一个小控制条（上一张、"4 / 12"、下一张、Notes、计时、Exit），角落还有一个 Exit；每个动画步骤显示其最终状态，不播放任何动画。Notes 打开显示本张备注的条带。设为自动播放的媒体剪辑在其幻灯片出现时开始播放，点按剪辑可播放或暂停，切换到其他幻灯片或 Exit 时停止 | `deck.show`、`deck.view {step}`、`deck.slide`、`deck.media` |
+| 放映 | 幻灯片单独显示在占满整个屏幕的深色舞台上：点按 Present 时会请 Shell 让窗口进入全屏（`window.fullscreen`）；宿主做不到时（card-host、手机），舞台占满应用窗口。下方一个小控制条（上一张、"4 / 12"、下一张、Notes、计时、Exit），角落还有一个 Exit；全屏时 Esc 是 Shell 的按键，也会结束放映，窗口恢复原样。每个动画步骤显示其最终状态，不播放任何动画；为较小窗口渲染的幻灯片会按全屏尺寸重新渲染。Notes 打开显示本张备注的条带。设为自动播放的媒体剪辑在其幻灯片出现时开始播放，点按剪辑可播放或暂停，切换到其他幻灯片或 Exit 时停止 | `deck.show`、`deck.view {step}`、`deck.slide`、`deck.media`；Shell 的 `window.fullscreen` |
 | 导出 | Presentation（.pptx）、PDF（幻灯片、备注页或讲义，每页 1 到 9 张）或 Images（每张幻灯片一个 PNG）；全部幻灯片、当前幻灯片或一个范围；是否包含隐藏的幻灯片；名称。列出该演示文稿以前的导出，并可删除 | `deck.export` |
 
 Undo 和 Redo 使用引擎的历史记录；Save 写入原生 `.deckcraft` 文件（`deck.undo`、`deck.redo`、`deck.save`、`deck.state`）。关闭有未保存更改的标签时会询问：保存、不保存或取消。
diff --git a/apps/quickdeck/bundle/main.splash b/apps/quickdeck/bundle/main.splash
index 928d0b2f..ae1f740a 100644
--- a/apps/quickdeck/bundle/main.splash
+++ b/apps/quickdeck/bundle/main.splash
@@ -1092,6 +1092,7 @@ if st == nil {
         heartbeat: nil        // the interval below, made once
         index_dirty: false    // library.json waits for the heartbeat
         present: nil          // the show going on
+        screen_full: false    // the shell has the window in full screen for Present (on_app_fullscreen)
         next_key: 1
         insp_over: false      // a narrow window shows the inspector over the canvas
         clip: nil             // the clip playing or getting ready (playback, below)
@@ -3156,14 +3157,21 @@ fn start_present(t){
             return
         }
         // media: each slide's clips (deck.slide); autoplayed: the slide on
-        // show has started its clip by itself (playback).
-        st.present = {key: t.key order: order i: 0 step: 0 notes: st.show_notes started: time_now() pics: {} failed: {} full: {} timer: nil done: false
+        // show has started its clip by itself (playback); px: the width each
+        // picture was drawn at, so a bigger stage draws it again.
+        st.present = {key: t.key order: order i: 0 step: 0 notes: st.show_notes started: time_now() pics: {} px: {} failed: {} full: {} timer: nil done: false
             media: {} autoplayed: {}}
         st.present.timer = start_interval(1, || present_tick())
         // The stage shows the slide alone: an earlier note goes.
         note("")
         show()
         pump()
+        // The Present tap also asks the shell for the whole screen
+        // (window.fullscreen), within the 5 seconds a press counts for.
+        // Where it can't (a host with no window service, such as card-host,
+        // or a refusal), the show fills the window as before, and the answer
+        // is not shown.
+        host.request("window.fullscreen", {on: true}, fn(r){})
     })
 }
 fn present_tab(){
@@ -3190,7 +3198,10 @@ fn present_next(){
     if p.step >= optional(item, "steps", 0) && p.i + 1 < p.order.len() { want.push({item: p.order[p.i + 1] step: 0}) }
     for i w in want {
         let k = present_key(w.item, w.step)
-        if optional(p.pics, k, nil) == nil && optional(p.failed, k, nil) == nil {
+        // A picture drawn for a smaller stage (before the window went full
+        // screen) is drawn again; it shows, stretched, until then.
+        let stale = optional(p.pics, k, nil) == nil || optional(p.px, k, 0) != stage_px()
+        if stale && optional(p.failed, k, nil) == nil {
             present_render(t, w.item, w.step)
             return true
         }
@@ -3231,13 +3242,17 @@ fn present_notes(t, item){
 fn present_render(t, item, step){
     let p = st.present
     let k = present_key(item, step)
+    let px = stage_px()
     busy_on()
-    engine("view", {doc: t.doc slide: item.slide width: stage_px() step: step}, fn(a){
+    engine("view", {doc: t.doc slide: item.slide width: px step: step}, fn(a){
         st.busy = false
         if st.present != p { return }
         let src = nil
         if a.is_ok { src = read_png(optional(a.data, "path", "")) }
-        if src != nil { p.pics[k] = src } else { p.failed[k] = true }
+        if src != nil {
+            p.pics[k] = src
+            p.px[k] = px
+        } else { p.failed[k] = true }
         let now = present_item()
         if now != nil && present_key(now, p.step) == k { render_present() }
         later_pump()
@@ -3304,6 +3319,21 @@ fn stop_present(){
     if t != nil && item != nil { go_slide(t, item.slide) }
     pump()
 }
+// The shell's word that the window's full screen started or ended: when Esc,
+// ⌘F or another window ends it, Present ends too. One that starts after
+// Present already ended goes straight back.
+fn on_app_fullscreen(on){
+    st.screen_full = on
+    if on { screen_back() } else { stop_present() }
+}
+// The full screen Present asked for goes back once Present is over, however
+// it ended: Exit, the corner control or the end of the show (show() asks
+// after every change).
+fn screen_back(){
+    if !optional(st, "screen_full", false) || st.present != nil { return }
+    st.screen_full = false
+    host.request("window.fullscreen", {on: false}, fn(r){})
+}
 
 // ---- playback -------------------------------------------------------------------
 // One clip plays at a time: in the editor, the chosen clip, from its control
@@ -4004,6 +4034,7 @@ fn show_regions(){
 fn show(){
     // Another tab, view or screen stops a clip (playback).
     clip_check()
+    screen_back()
     let t = cur_tab()
     let presenting = st.present != nil
     let deck = !presenting && t != nil && t.kind == "deck"
diff --git a/apps/quickdeck/tests/ui.py b/apps/quickdeck/tests/ui.py
index a3c4d226..d87f1a32 100644
--- a/apps/quickdeck/tests/ui.py
+++ b/apps/quickdeck/tests/ui.py
@@ -39,7 +39,9 @@
   shell    a deck made from an outline, then edited: text in place, a format,
            a chart inserted and its data changed, a layout, a theme, the sorter
            (duplicate, hide, a section), notes, undo and redo, save, export
-           (.pptx, PDF and pictures), Present and its notes, light, then dark
+           (.pptx, PDF and pictures), Present and its notes (the show takes
+           the window full screen, window.fullscreen, and gives it back: by
+           Exit in the light pass, by Esc in the dark one), light, then dark
            through the shell's own style menu; in the light pass the
            inspector's states follow real changes and their undo: a box's
            anchor and autofit, a chart element, a table option, the colour set
@@ -53,8 +55,9 @@
            (.cache/media/<sha256>.<ext>, checked against the clip's own
            bytes) and the Video widget plays it where the system has a player
            (a Mac: two grabs a second apart differ) or says "Playback isn't
-           available on this system" (Linux), in the editor and in Present,
-           light, then dark; a closed deck's clips leave the cache. On a Mac
+           available on this system" (Linux), in the editor and in Present
+           (which takes the window full screen, the clip playing on through
+           it), light, then dark; a closed deck's clips leave the cache. On a Mac
            it never plays the sound (the runs open no audio device)
 
 Shell runs hold a lock folder, so one hidden shell runs on this machine at a
@@ -454,6 +457,25 @@ def wait_until(check, failure, timeout=30.0):
     raise AssertionError(failure)
 
 
+def window_rect(app):
+    """The whole window, in points: what a full-screen window covers."""
+    w, h = app.size()
+    return [0, 0, w, h]
+
+
+def same_rect(a, b):
+    return len(a) == len(b) and all(abs(x - y) < 1.5 for x, y in zip(a, b))
+
+
+def full_screen(app):
+    """Wait until the app covers the whole window: Present's tap asked the
+    shell for full screen (window.fullscreen). A hidden shell never asks the
+    host window itself, so the window is the screen here."""
+    wait_until(lambda: same_rect(app.area(), window_rect(app)),
+               f"the app did not go full screen: {app.area()} in {window_rect(app)}")
+    return app.area()
+
+
 def slide_rect(app):
     """The canvas's slide picture: [x, y, w, h] in points (the largest picture
     right of the navigator and left of the inspector)."""
@@ -927,6 +949,24 @@ def stage_rect(app):
     return max(imgs, key=lambda r: r[2] * r[3])
 
 
+def stage_settled(app, timeout=20.0):
+    """Present's slide picture once it stops moving: in a shell the show goes
+    full screen just after it starts, and the stage grows with the window."""
+    deadline = time.monotonic() + timeout
+    last, same = None, 0
+    while time.monotonic() < deadline:
+        try:
+            rect = stage_rect(app)
+        except AssertionError:
+            rect = None
+        same = same + 1 if rect is not None and rect == last else 0
+        if same >= 3:
+            return rect
+        last = rect
+        time.sleep(0.4)
+    raise AssertionError(f"Present's slide never settled; last {last}")
+
+
 def box_on(rect, box):
     """A clip's box (slide points) on screen, in the slide picture `rect`."""
     x, y, w, h = rect
@@ -1141,11 +1181,13 @@ def shell_playback(app, out, dark, home):
         app.find("Paused.", "Label", timeout=10)
         app.tap("Stop")
     still_open(app, "the editor's playback")
-    # Present: the video plays by itself (a native deck keeps autoplay).
+    # Present: the video plays by itself (a native deck keeps autoplay), and
+    # keeps playing as the show takes the window full screen.
     app.tap("Present", "Button")
     app.find("Exit", "Button", timeout=60)
+    full_screen(app)
     app.images(1, timeout=60)
-    stage = box_on(stage_rect(app), LAUNCH_FILM)
+    stage = box_on(stage_settled(app), LAUNCH_FILM)
     if LINUX:
         wait_until(lambda: stage_note(app) == NO_PLAYER, "the show's clip never said it can't play", timeout=40)
         app.grab(out, f"{p}p2-present-unavailable")
@@ -1189,10 +1231,11 @@ def shell_playback(app, out, dark, home):
     app.find("Starts when it's tapped.", "Label", timeout=30)
     app.tap("Present", "Button")
     app.find("Exit", "Button", timeout=60)
+    full_screen(app)
     app.images(1, timeout=60)
     time.sleep(2.0)
     assert stage_note(app) is None, f"a .pptx clip started by itself: {stage_note(app)}"
-    stage = box_on(stage_rect(app), LAUNCH_FILM)
+    stage = box_on(stage_settled(app), LAUNCH_FILM)
     app.click(stage[0] + stage[2] / 2, stage[1] + stage[3] / 2)
     if LINUX:
         wait_until(lambda: stage_note(app) == NO_PLAYER, "the tapped clip never said it can't play", timeout=40)
@@ -1336,14 +1379,27 @@ def shell_journey(app, out, dark):
     app.grab(out, f"{p}08-export")
     app.scroll(-3000)
     app.tap("Export", "Button")
-    # present
+    # present: the tap takes the whole screen (window.fullscreen); the light
+    # pass leaves by Exit, the dark one by Esc, the shell's key in full
+    # screen (a script gets no keys), and the window comes back either way.
     go_to(app, 1)
+    windowed = app.area()
     app.tap("Present", "Button")
     app.find("Exit", "Button", timeout=60)
+    full = full_screen(app)
     app.images(1, timeout=60)
     app.grab(out, f"{p}09-present")
     app.click(app.area()[2] / 2, app.area()[3] / 2)
-    app.tap("Exit", "Button")
+    if dark:
+        app.key("Escape")
+    else:
+        app.tap("Exit", "Button")
+    app.find("Present", "Button", timeout=30)
+    app.gone("Exit")
+    wait_until(lambda: same_rect(app.area(), windowed),
+               f"the window did not come back after Present: {app.area()}, was {windowed}")
+    (out / f"{p}present-full-screen.json").write_text(json.dumps(
+        {"window": windowed, "full_screen": full, "after": app.area(), "left_by": "Escape" if dark else "Exit"}, indent=1))
 
 
 def states_follow(app, out):