diff --git a/crates/ui-egui/src/chrome.rs b/crates/ui-egui/src/chrome.rs
index fb9e0a7c0d..491b316a35 100644
--- a/crates/ui-egui/src/chrome.rs
+++ b/crates/ui-egui/src/chrome.rs
@@ -638,148 +638,179 @@ pub fn right_rail(app: &mut PdfCraftApp, ui: &mut egui::Ui) {
         .exact_size(48.0)
         .frame(egui::Frame::NONE.fill(t.chrome).inner_margin(egui::Margin::symmetric(6, 8)).stroke(Stroke::new(1.0, t.divider)))
         .show(ui, |ui| {
-            ui.spacing_mut().item_spacing.y = 4.0;
-            let mut rail_button = |ui: &mut egui::Ui, panel: RightPanel, icon: &str, tip: &str, has: bool| {
-                let selected = app.right == Some(panel) && (app.mode == Mode::Read || app.docking.exposed(crate::docking::Panel::Inspector));
-                let r = icons::button(ui, icon, 34.0, selected, tl!(tip));
-                if has && !selected {
-                    let c = r.rect.right_top() + vec2(-8.0, 8.0);
-                    ui.painter().circle_filled(c, 3.0, t.accent);
-                }
-                if r.clicked() {
-                    app.choose_right_panel(if selected { None } else { Some(panel) });
-                }
-            };
-            rail_button(ui, RightPanel::Comments, "message-square-text", "Comments", has_comments);
-            rail_button(ui, RightPanel::Bookmarks, "bookmark", "Bookmarks", has_outline);
-            rail_button(ui, RightPanel::Pages, "files", "Page thumbnails", false);
-            rail_button(ui, RightPanel::Fields, "text-cursor-input", "Form fields", has_fields);
-            rail_button(ui, RightPanel::Layers, "layers", "Layers", has_layers);
-            rail_button(ui, RightPanel::Attachments, "paperclip", "Attachments", has_files);
-            rail_button(ui, RightPanel::Signatures, "signature", "Signatures", has_signatures);
-            if has_check {
-                rail_button(ui, RightPanel::Accessibility, "accessibility", "Accessibility Checker", false);
-            }
-            rail_button(ui, RightPanel::Tags, "tag", "Tags", false);
-
-            // Page navigation cluster at the bottom (as in Acrobat's rail).
-            let view = &mut app.views[index];
-            let mut page_display = None;
-            ui.with_layout(Layout::bottom_up(Align::Center), |ui| {
-                ui.spacing_mut().item_spacing.y = 2.0;
-                let tip = crate::commands::key_tip(ui.ctx(), tl!("Zoom out ({key})"), crate::commands::ZOOM_OUT);
-                if icons::button(ui, "zoom-out", 32.0, false, &tip).clicked() {
-                    view.zoom_step(false);
-                }
-                let tip = crate::commands::key_tip(ui.ctx(), tl!("Zoom in ({key})"), crate::commands::ZOOM_IN);
-                if icons::button(ui, "zoom-in", 32.0, false, &tip).clicked() {
-                    view.zoom_step(true);
-                }
-                // Between rotate and zoom, as in Acrobat. Its command runs once `view` is free.
-                let tip = crate::i18n::fmt(tl!("Page display: {layout}"), &[("layout", tl!(view.layout.label()))]);
-                let resp = icons::button(ui, view.layout.icon(), 32.0, false, &tip);
-                page_display = egui::Popup::menu(&resp)
-                    .show(|ui| {
-                        ui.set_min_width(220.0);
-                        rail_view_menu(ui, view)
-                    })
-                    .and_then(|r| r.inner);
-                let tip = crate::commands::key_tip(ui.ctx(), tl!("Rotate view clockwise ({key})"), crate::commands::ROTATE_CW);
-                if icons::button(ui, "rotate-cw", 32.0, false, &tip).clicked() {
-                    view.rotate_view(true);
-                }
-                // Not `columns-2` while fitting the page: that is the two-page view's icon.
-                let fit_icon = if view.fit == Fit::Width { "maximize" } else { "maximize-2" };
-                if icons::button(ui, fit_icon, 32.0, false, tl!("Toggle fit page / fit width")).clicked() {
-                    view.fit = if view.fit == Fit::Width { Fit::Page } else { Fit::Width };
-                    view.goto = Some((view.current, 0.0));
-                }
-                let id = egui::Id::new("zoom-input");
-                let draft = id.with("draft");
-                let mut typed = ui.data(|d| d.get_temp::<String>(draft)).unwrap_or_else(|| format!("{:.0}%", view.zoom * 100.0));
-                let edit = egui::TextEdit::singleline(&mut typed)
-                    .id(id)
-                    .desired_width(40.0)
-                    .horizontal_align(Align::Center)
-                    .font(theme::medium(11.0))
-                    .text_color(t.text_muted)
-                    .frame(egui::Frame::NONE)
-                    .margin(vec2(2.0, 2.0));
-                let r = ui.add(edit).on_hover_text(tl!("Zoom — type a percentage and press Enter"));
-                ui.ctx().accesskit_node_builder(id, |node| node.set_label(tl!("Zoom")));
-                if r.gained_focus() {
-                    let mut state = egui::TextEdit::load_state(ui.ctx(), id).unwrap_or_default();
-                    let all = egui::text::CCursorRange::two(egui::text::CCursor::new(0), egui::text::CCursor::new(typed.chars().count()));
-                    state.cursor.set_char_range(Some(all));
-                    state.store(ui.ctx(), id);
-                }
-                if r.has_focus() {
-                    ui.data_mut(|d| d.insert_temp(draft, typed.clone()));
-                } else {
-                    ui.data_mut(|d| d.remove::<String>(draft));
-                    if r.lost_focus()
-                        && ui.input(|i| i.key_pressed(egui::Key::Enter))
-                        && let Some(zoom) = DocView::parse_zoom_percent(&typed)
-                    {
-                        view.set_zoom(zoom);
+            // The heights of the panel buttons and of the navigation cluster on the last frame.
+            let heights_id = ui.id().with("rail_heights");
+            let measured = ui.data(|d| d.get_temp::<(f32, f32)>(heights_id));
+            let (top, nav) = measured.unwrap_or_default();
+            let height = ui.available_height();
+            // Too short for both groups (a small window, or a large interface size), the rail
+            // scrolls instead of drawing the navigation over the panel buttons (#2891). A rail
+            // that fits keeps the plain layout, so neither it nor the canvas beside it moves.
+            let overflows = top + 4.0 + nav > height;
+            let mut body = |ui: &mut egui::Ui| {
+                // From the cursor: a panel's own rect is already as tall as the window.
+                let start = ui.cursor().top();
+                ui.spacing_mut().item_spacing.y = 4.0;
+                let mut rail_button = |ui: &mut egui::Ui, panel: RightPanel, icon: &str, tip: &str, has: bool| {
+                    let selected = app.right == Some(panel) && (app.mode == Mode::Read || app.docking.exposed(crate::docking::Panel::Inspector));
+                    let r = icons::button(ui, icon, 34.0, selected, tl!(tip));
+                    if has && !selected {
+                        let c = r.rect.right_top() + vec2(-8.0, 8.0);
+                        ui.painter().circle_filled(c, 3.0, t.accent);
                     }
-                }
-                ui.add_space(6.0);
-                if icons::button(ui, "chevron-down", 30.0, false, tl!("Next page")).clicked() {
-                    view.step_page(true);
-                }
-                if icons::button(ui, "chevron-up", 30.0, false, tl!("Previous page")).clicked() {
-                    view.step_page(false);
-                }
-                // History is distinct from stepping to the adjacent page, and belongs to this tab.
-                for (forward, icon, label, shortcut, enabled) in [
-                    (true, "chevron-right", tl!("Next view"), crate::commands::NEXT_VIEW, !view.forward.is_empty()),
-                    (false, "chevron-left", tl!("Previous view"), crate::commands::PREV_VIEW, !view.back.is_empty()),
-                ] {
-                    let tip = format!("{label} ({})", crate::commands::shortcut_label(ui.ctx(), shortcut));
-                    if ui.add_enabled_ui(enabled, |ui| icons::button(ui, icon, 30.0, false, &tip)).inner.clicked() {
-                        view.view_history(forward);
+                    if r.clicked() {
+                        app.choose_right_panel(if selected { None } else { Some(panel) });
                     }
-                }
-                ui.label(egui::RichText::new(page_count.to_string()).font(theme::regular(11.0)).color(t.text_muted));
-                let page_input_id = view.page_input_id();
-                // Consume replacement selection once, including when the editor has lost focus.
-                let reselect = std::mem::take(&mut view.page_input_reselect);
-                // Navigation updates the idle display, never the text being edited.
-                if !ui.memory(|m| m.has_focus(page_input_id)) {
-                    view.page_input = view.current_page_label(labels.get(view.current).map(String::as_str));
-                } else if reselect {
-                    // The replacement changed the label while egui retained this editor's cursor.
-                    let mut state = egui::TextEdit::load_state(ui.ctx(), page_input_id).unwrap_or_default();
-                    let end = egui::text::CCursor::new(view.page_input.chars().count());
-                    state.cursor.set_char_range(Some(egui::text::CCursorRange::two(egui::text::CCursor::new(0), end)));
-                    state.store(ui.ctx(), page_input_id);
-                }
-                let edit = egui::TextEdit::singleline(&mut view.page_input)
-                    .id(page_input_id)
-                    .desired_width(34.0)
-                    .horizontal_align(Align::Center)
-                    .font(theme::medium(12.0))
-                    .margin(vec2(2.0, 4.0));
-                let r = egui::Frame::NONE
-                    .fill(t.field)
-                    .stroke(Stroke::new(1.0, t.border))
-                    .corner_radius(CornerRadius::same(5))
-                    .show(ui, |ui| ui.add(edit))
-                    .inner
-                    .on_hover_text(tl!("Current page — type a page number or label (such as iv) and press Enter"));
-                if r.lost_focus() {
-                    if ui.input(|i| i.key_pressed(egui::Key::Enter)) {
-                        // A page label first (logical page numbers, as Acrobat), then a number.
-                        let typed = view.page_input.clone();
-                        view.go_to_typed(&typed, &labels);
+                };
+                rail_button(ui, RightPanel::Comments, "message-square-text", "Comments", has_comments);
+                rail_button(ui, RightPanel::Bookmarks, "bookmark", "Bookmarks", has_outline);
+                rail_button(ui, RightPanel::Pages, "files", "Page thumbnails", false);
+                rail_button(ui, RightPanel::Fields, "text-cursor-input", "Form fields", has_fields);
+                rail_button(ui, RightPanel::Layers, "layers", "Layers", has_layers);
+                rail_button(ui, RightPanel::Attachments, "paperclip", "Attachments", has_files);
+                rail_button(ui, RightPanel::Signatures, "signature", "Signatures", has_signatures);
+                if has_check {
+                    rail_button(ui, RightPanel::Accessibility, "accessibility", "Accessibility Checker", false);
+                }
+                rail_button(ui, RightPanel::Tags, "tag", "Tags", false);
+
+                let top = ui.cursor().top() - start;
+
+                // Page navigation cluster at the bottom (as in Acrobat's rail).
+                let view = &mut app.views[index];
+                let mut page_display = None;
+                let cluster = |ui: &mut egui::Ui| {
+                    ui.spacing_mut().item_spacing.y = 2.0;
+                    let tip = crate::commands::key_tip(ui.ctx(), tl!("Zoom out ({key})"), crate::commands::ZOOM_OUT);
+                    if icons::button(ui, "zoom-out", 32.0, false, &tip).clicked() {
+                        view.zoom_step(false);
+                    }
+                    let tip = crate::commands::key_tip(ui.ctx(), tl!("Zoom in ({key})"), crate::commands::ZOOM_IN);
+                    if icons::button(ui, "zoom-in", 32.0, false, &tip).clicked() {
+                        view.zoom_step(true);
+                    }
+                    // Between rotate and zoom, as in Acrobat. Its command runs once `view` is free.
+                    let tip = crate::i18n::fmt(tl!("Page display: {layout}"), &[("layout", tl!(view.layout.label()))]);
+                    let resp = icons::button(ui, view.layout.icon(), 32.0, false, &tip);
+                    page_display = egui::Popup::menu(&resp)
+                        .show(|ui| {
+                            ui.set_min_width(220.0);
+                            rail_view_menu(ui, view)
+                        })
+                        .and_then(|r| r.inner);
+                    let tip = crate::commands::key_tip(ui.ctx(), tl!("Rotate view clockwise ({key})"), crate::commands::ROTATE_CW);
+                    if icons::button(ui, "rotate-cw", 32.0, false, &tip).clicked() {
+                        view.rotate_view(true);
+                    }
+                    // Not `columns-2` while fitting the page: that is the two-page view's icon.
+                    let fit_icon = if view.fit == Fit::Width { "maximize" } else { "maximize-2" };
+                    if icons::button(ui, fit_icon, 32.0, false, tl!("Toggle fit page / fit width")).clicked() {
+                        view.fit = if view.fit == Fit::Width { Fit::Page } else { Fit::Width };
+                        view.goto = Some((view.current, 0.0));
+                    }
+                    let id = egui::Id::new("zoom-input");
+                    let draft = id.with("draft");
+                    let mut typed = ui.data(|d| d.get_temp::<String>(draft)).unwrap_or_else(|| format!("{:.0}%", view.zoom * 100.0));
+                    let edit = egui::TextEdit::singleline(&mut typed)
+                        .id(id)
+                        .desired_width(40.0)
+                        .horizontal_align(Align::Center)
+                        .font(theme::medium(11.0))
+                        .text_color(t.text_muted)
+                        .frame(egui::Frame::NONE)
+                        .margin(vec2(2.0, 2.0));
+                    let r = ui.add(edit).on_hover_text(tl!("Zoom — type a percentage and press Enter"));
+                    ui.ctx().accesskit_node_builder(id, |node| node.set_label(tl!("Zoom")));
+                    if r.gained_focus() {
+                        let mut state = egui::TextEdit::load_state(ui.ctx(), id).unwrap_or_default();
+                        let all = egui::text::CCursorRange::two(egui::text::CCursor::new(0), egui::text::CCursor::new(typed.chars().count()));
+                        state.cursor.set_char_range(Some(all));
+                        state.store(ui.ctx(), id);
+                    }
+                    if r.has_focus() {
+                        ui.data_mut(|d| d.insert_temp(draft, typed.clone()));
+                    } else {
+                        ui.data_mut(|d| d.remove::<String>(draft));
+                        if r.lost_focus()
+                            && ui.input(|i| i.key_pressed(egui::Key::Enter))
+                            && let Some(zoom) = DocView::parse_zoom_percent(&typed)
+                        {
+                            view.set_zoom(zoom);
+                        }
+                    }
+                    ui.add_space(6.0);
+                    if icons::button(ui, "chevron-down", 30.0, false, tl!("Next page")).clicked() {
+                        view.step_page(true);
+                    }
+                    if icons::button(ui, "chevron-up", 30.0, false, tl!("Previous page")).clicked() {
+                        view.step_page(false);
                     }
-                    view.page_input = view.current_page_label(labels.get(view.current).map(String::as_str));
+                    // History is distinct from stepping to the adjacent page, and belongs to this tab.
+                    for (forward, icon, label, shortcut, enabled) in [
+                        (true, "chevron-right", tl!("Next view"), crate::commands::NEXT_VIEW, !view.forward.is_empty()),
+                        (false, "chevron-left", tl!("Previous view"), crate::commands::PREV_VIEW, !view.back.is_empty()),
+                    ] {
+                        let tip = format!("{label} ({})", crate::commands::shortcut_label(ui.ctx(), shortcut));
+                        if ui.add_enabled_ui(enabled, |ui| icons::button(ui, icon, 30.0, false, &tip)).inner.clicked() {
+                            view.view_history(forward);
+                        }
+                    }
+                    ui.label(egui::RichText::new(page_count.to_string()).font(theme::regular(11.0)).color(t.text_muted));
+                    let page_input_id = view.page_input_id();
+                    // Consume replacement selection once, including when the editor has lost focus.
+                    let reselect = std::mem::take(&mut view.page_input_reselect);
+                    // Navigation updates the idle display, never the text being edited.
+                    if !ui.memory(|m| m.has_focus(page_input_id)) {
+                        view.page_input = view.current_page_label(labels.get(view.current).map(String::as_str));
+                    } else if reselect {
+                        // The replacement changed the label while egui retained this editor's cursor.
+                        let mut state = egui::TextEdit::load_state(ui.ctx(), page_input_id).unwrap_or_default();
+                        let end = egui::text::CCursor::new(view.page_input.chars().count());
+                        state.cursor.set_char_range(Some(egui::text::CCursorRange::two(egui::text::CCursor::new(0), end)));
+                        state.store(ui.ctx(), page_input_id);
+                    }
+                    let edit = egui::TextEdit::singleline(&mut view.page_input)
+                        .id(page_input_id)
+                        .desired_width(34.0)
+                        .horizontal_align(Align::Center)
+                        .font(theme::medium(12.0))
+                        .margin(vec2(2.0, 4.0));
+                    let r = egui::Frame::NONE
+                        .fill(t.field)
+                        .stroke(Stroke::new(1.0, t.border))
+                        .corner_radius(CornerRadius::same(5))
+                        .show(ui, |ui| ui.add(edit))
+                        .inner
+                        .on_hover_text(tl!("Current page — type a page number or label (such as iv) and press Enter"));
+                    if r.lost_focus() {
+                        if ui.input(|i| i.key_pressed(egui::Key::Enter)) {
+                            // A page label first (logical page numbers, as Acrobat), then a number.
+                            let typed = view.page_input.clone();
+                            view.go_to_typed(&typed, &labels);
+                        }
+                        view.page_input = view.current_page_label(labels.get(view.current).map(String::as_str));
+                    }
+                };
+                // Scrolling, the cluster goes below the buttons at its height from the last frame.
+                let nav = if overflows {
+                    ui.allocate_ui_with_layout(vec2(ui.available_width(), nav), Layout::bottom_up(Align::Center), cluster).response.rect
+                } else {
+                    ui.with_layout(Layout::bottom_up(Align::Center), cluster).response.rect
+                };
+                if let Some(id) = page_display {
+                    app.execute(id);
                 }
-            });
-            if let Some(id) = page_display {
-                app.execute(id);
+                (top, nav.height())
+            };
+            let heights =
+                if overflows { egui::ScrollArea::vertical().id_salt("rail").auto_shrink([false, false]).show(ui, body).inner } else { body(ui) };
+            // This pass laid the groups out as if they fit, unmeasured or with the heights of a
+            // shorter rail (a button added since): when they don't, it is redone with the new
+            // heights rather than shown overlapping for a frame. Redone, it scrolls.
+            if !overflows && heights.0 + 4.0 + heights.1 > height {
+                ui.ctx().request_discard("right rail measured its groups");
             }
+            ui.data_mut(|d| d.insert_temp(heights_id, heights));
         });
 }
 
diff --git a/crates/ui-egui/tests/ui.rs b/crates/ui-egui/tests/ui.rs
index b86f7699f0..e35c65f900 100644
--- a/crates/ui-egui/tests/ui.rs
+++ b/crates/ui-egui/tests/ui.rs
@@ -192,6 +192,82 @@ fn read_mode_rail_buttons_open_their_panels() {
     h.get_by_label("Alpha section");
 }
 
+/// The rail's panel buttons and its page navigation never overlap (#2891). A 1080 px tall
+/// window is 720 pt at 150 % interface size and 540 pt at 200 %, both too short for the two
+/// groups: the rail scrolls instead of drawing one over the other.
+#[test]
+fn a_short_rail_scrolls_instead_of_overlapping_its_controls() {
+    for scale in ["150%", "200%"] {
+        let mut h = Harness::builder().with_size(egui::vec2(1920.0, 1080.0)).build_eframe(move |_cc| {
+            let mut app = PdfCraftApp::new();
+            app.set_option("language", "en").unwrap();
+            app.set_option("ui-scale", scale).unwrap();
+            app.open_bytes("fixture.pdf", None, FIXTURE.to_vec()).expect("fixture opens");
+            app
+        });
+        h.run_steps(6);
+        assert_rail_controls_apart(&h, scale);
+    }
+}
+
+/// The rail has not measured its two groups on the frame it first appears, and that frame is
+/// the one shown: it must not overlap either, not only the frames after it.
+#[test]
+fn a_short_rail_does_not_overlap_on_its_first_frame() {
+    let mut h = Harness::builder().with_size(egui::vec2(1920.0, 1080.0)).build_eframe(|_cc| {
+        let mut app = PdfCraftApp::new();
+        app.set_option("language", "en").unwrap();
+        app.set_option("ui-scale", "200%").unwrap();
+        app
+    });
+    h.run_steps(4);
+    h.state_mut().open_bytes("fixture.pdf", None, FIXTURE.to_vec()).expect("fixture opens");
+    h.step();
+    assert_rail_controls_apart(&h, "200%");
+}
+
+/// A rail that fits can grow past its height between two frames: checking for accessibility adds
+/// its button. At 785 pt the groups fit without it and not with it, and the frame where it appears
+/// is laid out with the heights of the frame before: it must not overlap either.
+#[test]
+fn a_rail_that_grows_past_its_height_does_not_overlap_for_a_frame() {
+    let mut h = Harness::builder().with_size(egui::vec2(1400.0, 785.0)).build_eframe(|_cc| {
+        let mut app = PdfCraftApp::new();
+        app.set_option("language", "en").unwrap();
+        app.open_bytes("fixture.pdf", None, FIXTURE.to_vec()).expect("fixture opens");
+        app
+    });
+    h.run_steps(6);
+    assert!(h.query_by_label("Accessibility Checker").is_none());
+    assert_rail_controls_apart(&h, "100%");
+    h.state_mut().run_accessibility_check();
+    h.step();
+    let tags = h.get_by_label("Tags").rect();
+    assert!(h.query_all_by_label("Accessibility Checker").any(|n| (tags.left()..tags.right()).contains(&n.rect().center().x)), "the rail has grown");
+    assert_rail_controls_apart(&h, "100%");
+}
+
+fn assert_rail_controls_apart(h: &Harness<'_, PdfCraftApp>, scale: &str) {
+    use egui::accesskit::Role;
+    use egui_kittest::kittest::by;
+    let tags = h.get_by_label("Tags").rect();
+    let in_rail = |r: &egui::Rect| r.center().x > tags.left() - 4.0 && r.center().x < tags.right() + 4.0;
+    let rail: Vec<(String, egui::Rect)> = h
+        .query_all(by().predicate(|n| matches!(n.role(), Role::Button | Role::TextInput | Role::Label)))
+        .map(|n| (n.accesskit_node().label().unwrap_or_default(), n.rect()))
+        .filter(|(_, r)| in_rail(r))
+        .collect();
+    for label in ["Tags", "Signatures", "Zoom out", "Next page", "Previous view", "Page display"] {
+        assert!(rail.iter().any(|(l, _)| l.starts_with(label)), "{scale}: the rail has {label}: {rail:?}");
+    }
+    for (i, (a, ra)) in rail.iter().enumerate() {
+        for (b, rb) in &rail[i + 1..] {
+            let o = ra.intersect(*rb);
+            assert!(o.width() <= 0.5 || o.height() <= 0.5, "{scale}: {a:?} {ra:?} overlaps {b:?} {rb:?}");
+        }
+    }
+}
+
 /// A document that asks to open in Full Screen mode (`/PageMode /FullScreen`) is asked about
 /// first, as in Acrobat: "Not now" leaves the window as it is, "Full Screen" enters it.
 #[test]