diff --git a/crates/ui-egui/src/panels/timeline.rs b/crates/ui-egui/src/panels/timeline.rs
index d7017e7fd..be0ef05d5 100644
--- a/crates/ui-egui/src/panels/timeline.rs
+++ b/crates/ui-egui/src/panels/timeline.rs
@@ -22,7 +22,9 @@ use crate::icons::{self, Icon};
 use crate::theme::Tokens;
 use crate::{EffectcraftApp, widgets};
 
-#[derive(Clone, Debug)]
+mod marquee;
+
+#[derive(Clone, Debug, PartialEq)]
 enum RowKind {
     Layer,
     Group {
@@ -328,7 +330,7 @@ fn focus_expression(ctx: &egui::Context, prop: u64, select: [usize; 2]) {
     ctx.data_mut(|d| d.insert_temp(expr_focus_id(), ExprFocus { prop, select, pass }));
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, PartialEq)]
 struct Row {
     layer: LayerId,
     depth: usize,
@@ -1969,8 +1971,6 @@ pub fn show(app: &mut EffectcraftApp, ui: &mut egui::Ui, rect: Rect) {
     g.max_scroll = (total_h - g.rows_rect.height() + g.rh).max(0.0);
     g.rows = rows;
     reveal_scroll(app, g);
-    wheel_zoom_scroll(app, ui, g);
-    pick_whip_edge_scroll(app, g);
     let snap_project = app.session.project.clone();
     let snap_expr = app.session.expr.clone();
     let ectx = EvalCtx {
@@ -1986,6 +1986,10 @@ pub fn show(app: &mut EffectcraftApp, ui: &mut egui::Ui, rect: Rect) {
     };
     let mut rw = begin_rows(app, ui, tl);
     let g = &mut rw;
+    marquee::prepare(app, ui, g);
+    wheel_zoom_scroll(app, ui, &g.tl);
+    pick_whip_edge_scroll(app, &g.tl);
+    marquee::scroll(app, g);
     draw_rows(app, ui, g, &ectx);
     ui.set_clip_rect(g.full_clip);
     background_menus(app, ui, g);
@@ -1997,7 +2001,7 @@ pub fn show(app: &mut EffectcraftApp, ui: &mut egui::Ui, rect: Rect) {
     group_reorder_drag(ui, g);
     quick_offset_follow(g);
     key_drag_follow(app, g);
-    box_select(app, ui, g);
+    marquee::finish(app, ui, g);
     current_time_indicator(app, g);
     let footer = footer_bar(app, ui, g);
     footer_zoom(app, ui, g, footer);
@@ -4460,7 +4464,7 @@ fn background_menus(app: &mut EffectcraftApp, ui: &mut egui::Ui, g: &mut Rw) {
     }
 }
 
-/// Click on the empty outline (its drag is the Timeline's one box, [`box_select`]).
+/// Click on the empty outline (its drag is the Timeline's one box, [`marquee`]).
 fn outline_marquee(ui: &mut egui::Ui, g: &mut Rw) {
     let actions = &mut g.tl.actions;
     let outline_empty = g.outline_empty.clone();
@@ -4578,7 +4582,7 @@ fn alt_scale_and_graph(app: &mut EffectcraftApp, ui: &mut egui::Ui, g: &mut Rw,
     // below the last row) deselects the layers and their keys and properties, as in After
 }
 
-/// Click on empty track area (its drag is the Timeline's one box, [`box_select`]).
+/// Click on empty track area (its drag is the Timeline's one box, [`marquee`]).
 fn graph_empty_area(ui: &mut egui::Ui, g: &mut Rw) {
     let actions = &mut g.tl.actions;
     let empty = g.empty.clone();
@@ -4797,80 +4801,6 @@ fn keys_in_box(comp: &Comp, rows: &[Row], tm: &TMap, top: f32, rh: f32, br: Rect
     keys
 }
 
-/// What a box over the Timeline selects: the layer rows it crosses (locked layers stay out) and
-/// the keys whose markers it touches. A box that reaches the outline (started on either side)
-/// selects the rows it crosses; one kept inside the time graph selects keys only, as before.
-/// Keys exist only in the time graph, so the box is cut at its left edge (`graph_x0`; a key
-/// scrolled out under the outline isn't touched).
-/// `graph_on`: the Graph Editor shows no key markers here.
-#[allow(clippy::too_many_arguments)]
-fn box_targets(
-    comp: &Comp,
-    rows: &[Row],
-    hit_rows: &[(Rect, Row)],
-    tm: &TMap,
-    top: f32,
-    rh: f32,
-    graph_x0: f32,
-    graph_on: bool,
-    br: Rect,
-) -> (Vec<u64>, Vec<effectcraft_engine::KeyRef>) {
-    let layers = hit_rows
-        .iter()
-        .filter(|(r, row)| br.min.x < graph_x0 && matches!(row.kind, RowKind::Layer) && r.intersects(br))
-        .filter(|(_, row)| comp.layer(row.layer).is_some_and(|l| !l.switches.locked))
-        .map(|(_, row)| row.layer.0)
-        .collect();
-    let in_graph = Rect::from_min_max(pos2(br.min.x.max(graph_x0), br.min.y), pos2(br.max.x, br.max.y));
-    let keys = if graph_on || in_graph.width() < 0.0 { vec![] } else { keys_in_box(comp, rows, tm, top, rh, in_graph) };
-    (layers, keys)
-}
-
-/// The Timeline's one selection box, from the empty outline or the empty time graph: it spans both
-/// columns as it is dragged (the pointer may cross the boundary either way) and on release selects
-/// the layer rows it crosses and the keys inside it, as in After Effects.
-fn box_select(app: &mut EffectcraftApp, ui: &mut egui::Ui, g: &mut Rw) {
-    let t = g.tl.t;
-    let tm = g.tl.tm;
-    let rows_rect = g.tl.rows_rect;
-    let rh = g.tl.rh;
-    let graph_x0 = g.tl.graph_x0;
-    let graph_on = g.graph_on;
-    let ctx = g.tl.ctx.clone();
-    let comp = g.tl.comp.clone();
-    let rows = g.tl.rows.clone();
-    let origin = [&g.outline_empty, &g.empty].into_iter().find(|r| r.dragged() || r.drag_stopped()).cloned();
-    let Some(origin) = origin else { return };
-    let box_of = |o: &egui::Response| {
-        let start = ctx.input(|i| i.pointer.press_origin());
-        start.zip(o.interact_pointer_pos().or_else(|| ctx.input(|i| i.pointer.latest_pos()))).map(|(a, b)| Rect::from_two_pos(a, b).intersect(rows_rect))
-    };
-    let id = egui::Id::unique("tl-box");
-    if origin.dragged()
-        && let Some(br) = box_of(&origin)
-    {
-        let bp = g.tl.p.with_clip_rect(rows_rect);
-        bp.rect_filled(br, 0.0, t.accent.gamma_multiply(0.12));
-        bp.rect_stroke(br, 0.0, Stroke::new(1.0, t.accent), StrokeKind::Inside);
-        ctx.data_mut(|d| d.insert_temp(id, br));
-    }
-    if origin.drag_stopped()
-        && let Some(br) = ctx.data(|d| d.get_temp::<Rect>(id))
-    {
-        ctx.data_mut(|d| d.remove::<Rect>(id));
-        let (layers, touched) = box_targets(&comp, &rows, &g.hit_rows, &tm, rows_rect.min.y - app.ui.timeline.scroll_y, rh, graph_x0, graph_on, br);
-        let mods = ui.input(|i| i.modifiers);
-        let add = mods.shift || mods.command;
-        let actions = &mut g.tl.actions;
-        // A box that catches nothing leaves nothing selected (layers included), unless it adds.
-        actions.push(("layer.select".into(), json!({"layers": layers, "add": add})));
-        if !touched.is_empty() {
-            let keys: Vec<serde_json::Value> = touched.iter().map(|k| json!({"layer": k.layer.0, "prop": k.prop, "time": k.time.seconds()})).collect();
-            actions.push(("keys.select".into(), json!({"keys": keys, "add": true, "selectProperties": true})));
-        }
-    }
-}
-
 fn current_time_indicator(app: &mut EffectcraftApp, g: &Rw) {
     let t = g.tl.t;
     let time = g.tl.time;
diff --git a/crates/ui-egui/src/panels/timeline/marquee.rs b/crates/ui-egui/src/panels/timeline/marquee.rs
new file mode 100644
index 000000000..d4eb56c76
--- /dev/null
+++ b/crates/ui-egui/src/panels/timeline/marquee.rs
@@ -0,0 +1,192 @@
+//! A marquee owns content coordinates; clipping belongs only to its painter.
+
+use std::sync::Arc;
+
+use effectcraft_engine::project::Comp;
+use egui::{Id, Pos2, Rect, Stroke, StrokeKind, pos2};
+use serde_json::json;
+
+use super::{Row, RowKind, Rw, TMap, edge_scroll_speed, keys_in_box, row_height};
+use crate::EffectcraftApp;
+
+#[derive(Clone)]
+struct Marquee {
+    owner: Id,
+    comp: Arc<Comp>,
+    rows: Arc<Vec<Row>>,
+    graph_on: bool,
+    layout: (Rect, f32, f32),
+    anchor: Anchor,
+    dragging: bool,
+}
+
+/// The pressed corner in content coordinates: a time (or an outline x) and a scroll-free y.
+#[derive(Clone, Copy)]
+pub(super) struct Anchor {
+    time: f64,
+    y: f32,
+    outline_x: Option<f32>,
+}
+
+/// The timeline layout a marquee is projected through.
+#[derive(Clone, Copy)]
+pub(super) struct View {
+    pub tm: TMap,
+    /// Screen y of the first row at scroll 0.
+    pub top: f32,
+    pub graph_x0: f32,
+    pub graph_on: bool,
+}
+
+impl View {
+    fn of(g: &Rw) -> Self {
+        Self { tm: g.tl.tm, top: g.tl.rows_rect.min.y, graph_x0: g.tl.graph_x0, graph_on: g.graph_on }
+    }
+}
+
+fn id() -> Id {
+    Id::unique("tl-marquee")
+}
+
+/// Capture on press, before wheel handling, even if the drag threshold is not crossed yet.
+pub(super) fn prepare(app: &EffectcraftApp, ui: &egui::Ui, g: &Rw) {
+    let ctx = &g.tl.ctx;
+    let (pressed, down, released, escape, focused) =
+        ctx.input(|i| (i.pointer.primary_pressed(), i.pointer.primary_down(), i.pointer.primary_released(), i.key_pressed(egui::Key::Escape), i.focused));
+    if let Some(mut drag) = ctx.data(|d| d.get_temp::<Marquee>(id())) {
+        let owned = ctx.dragged_id() == Some(drag.owner);
+        let dropped = released && ctx.drag_stopped_id() == Some(drag.owner);
+        let valid = ui.is_enabled()
+            && focused
+            && !escape
+            && Arc::ptr_eq(&drag.comp, &g.tl.comp)
+            && *drag.rows == *g.tl.rows
+            && drag.graph_on == g.graph_on
+            && drag.layout == (g.tl.rect, g.tl.rh, g.tl.graph_x0)
+            && (dropped || (down && (owned || (!drag.dragging && ctx.dragged_id().is_none()))));
+        drag.dragging |= owned;
+        ctx.data_mut(|d| {
+            if valid {
+                d.insert_temp(id(), drag);
+            } else {
+                d.remove::<Marquee>(id());
+            }
+        });
+    }
+    if pressed && ui.is_enabled() && focused && !escape {
+        let owner = [&g.outline_empty, &g.empty].into_iter().find(|r| r.is_pointer_button_down_on());
+        if let Some(owner) = owner
+            && let Some(p) = ctx.input(|i| i.pointer.press_origin())
+        {
+            ctx.data_mut(|d| {
+                d.insert_temp(
+                    id(),
+                    Marquee {
+                        owner: owner.id,
+                        comp: g.tl.comp.clone(),
+                        rows: g.tl.rows.clone(),
+                        graph_on: g.graph_on,
+                        layout: (g.tl.rect, g.tl.rh, g.tl.graph_x0),
+                        anchor: Anchor::press(&View::of(g), app.ui.timeline.scroll_y, p),
+                        dragging: false,
+                    },
+                );
+            });
+        }
+    }
+}
+
+/// Only the marquee owner scrolls, with the same bounded edge speed as a pick whip.
+pub(super) fn scroll(app: &mut EffectcraftApp, g: &Rw) {
+    let ctx = &g.tl.ctx;
+    if let Some(drag) = ctx.data(|d| d.get_temp::<Marquee>(id()))
+        && ctx.dragged_id() == Some(drag.owner)
+        && ctx.input(|i| i.pointer.primary_down())
+        && let Some(p) = ctx.input(|i| i.pointer.latest_pos())
+    {
+        let speed = edge_scroll_speed(g.tl.rows_rect, p.y, g.tl.rh);
+        let old = app.ui.timeline.scroll_y;
+        app.ui.timeline.scroll_y = (old + speed * ctx.input(|i| i.stable_dt).min(0.1)).clamp(0.0, g.tl.max_scroll);
+        if app.ui.timeline.scroll_y != old {
+            ctx.request_repaint();
+        }
+    }
+}
+
+pub(super) struct SelectionBox {
+    pub keys: Rect,
+    pub outline: bool,
+}
+
+impl Anchor {
+    /// Anchor a press at screen point `p` with the rows scrolled by `scroll`.
+    pub(super) fn press(v: &View, scroll: f32, p: Pos2) -> Self {
+        Self { time: v.tm.t(p.x.max(v.graph_x0)), y: p.y - v.top + scroll, outline_x: (p.x < v.graph_x0).then_some(p.x) }
+    }
+
+    /// Reproject the content anchor without clipping the logical selection bounds.
+    pub(super) fn selection(&self, v: &View, scroll: f32, pointer: Pos2) -> (Rect, SelectionBox) {
+        let tm = v.tm;
+        let anchor = pos2(self.outline_x.unwrap_or_else(|| tm.x(self.time)), v.top + self.y - scroll);
+        let paint = Rect::from_two_pos(anchor, pointer);
+        let graph = self.outline_x.is_none() || pointer.x >= v.graph_x0;
+        let keys =
+            if graph && !v.graph_on { Rect::from_two_pos(pos2(tm.x(self.time), anchor.y), pos2(pointer.x.max(v.graph_x0), pointer.y)) } else { Rect::NOTHING };
+        (paint, SelectionBox { keys, outline: self.outline_x.is_some() || pointer.x < v.graph_x0 })
+    }
+}
+
+/// Query all logical rows; the renderer's visible hit rows are not selection data.
+pub(super) fn targets(
+    comp: &Comp,
+    rows: &[Row],
+    tm: &TMap,
+    top: f32,
+    rh: f32,
+    paint: Rect,
+    selection: &SelectionBox,
+) -> (Vec<u64>, Vec<effectcraft_engine::KeyRef>) {
+    let mut layers = vec![];
+    let mut y = top;
+    for row in rows {
+        let bottom = y + row_height(row, rh);
+        if selection.outline
+            && matches!(row.kind, RowKind::Layer)
+            && y <= paint.max.y
+            && bottom >= paint.min.y
+            && comp.layer(row.layer).is_some_and(|l| !l.switches.locked)
+        {
+            layers.push(row.layer.0);
+        }
+        y = bottom;
+    }
+    (layers, keys_in_box(comp, rows, tm, top, rh, selection.keys))
+}
+
+/// Commit an owned primary release; otherwise paint without changing selection.
+pub(super) fn finish(app: &EffectcraftApp, ui: &egui::Ui, g: &mut Rw) {
+    let ctx = &g.tl.ctx;
+    let Some(drag) = ctx.data(|d| d.get_temp::<Marquee>(id())) else { return };
+    let released = ctx.input(|i| i.pointer.primary_released());
+    let dropped = released && ctx.drag_stopped_id() == Some(drag.owner);
+    if ctx.dragged_id() != Some(drag.owner) && !dropped {
+        return;
+    }
+    let Some(pointer) = ctx.input(|i| i.pointer.latest_pos()) else { return };
+    let (paint, selection) = drag.anchor.selection(&View::of(g), app.ui.timeline.scroll_y, pointer);
+    if dropped {
+        ctx.data_mut(|d| d.remove::<Marquee>(id()));
+        let (layers, keys) = targets(&g.tl.comp, &g.tl.rows, &g.tl.tm, g.tl.rows_rect.min.y - app.ui.timeline.scroll_y, g.tl.rh, paint, &selection);
+        let add = ui.input(|i| i.modifiers.shift || i.modifiers.command);
+        g.tl.actions.push(("layer.select".into(), json!({"layers": layers, "add": add})));
+        if !keys.is_empty() {
+            let keys: Vec<_> = keys.iter().map(|k| json!({"layer": k.layer.0, "prop": k.prop, "time": k.time.seconds()})).collect();
+            g.tl.actions.push(("keys.select".into(), json!({"keys": keys, "add": true, "selectProperties": true})));
+        }
+    } else {
+        let clip = if selection.outline { g.tl.rows_rect } else { g.right_clip };
+        let painter = g.tl.p.with_clip_rect(clip);
+        painter.rect_filled(paint, 0.0, g.tl.t.accent.gamma_multiply(0.12));
+        painter.rect_stroke(paint, 0.0, Stroke::new(1.0, g.tl.t.accent), StrokeKind::Inside);
+    }
+}
diff --git a/crates/ui-egui/src/panels/timeline/tests.rs b/crates/ui-egui/src/panels/timeline/tests.rs
index 983d80ae6..e42923e4a 100644
--- a/crates/ui-egui/src/panels/timeline/tests.rs
+++ b/crates/ui-egui/src/panels/timeline/tests.rs
@@ -959,25 +959,33 @@ fn a_box_over_both_columns_selects_the_rows_it_crosses_and_the_keys_inside() {
         rows.push(Row { layer: LayerId(*id), depth: 1, kind: RowKind::Prop { uid: uid(*id) } });
     }
     // Rows are 20 pt and 400 pt wide: the outline is left of x 200, a key at 0 s sits at x 205.
-    let hit_rows: Vec<(Rect, Row)> =
-        rows.iter().enumerate().map(|(i, r)| (Rect::from_min_size(pos2(0.0, 20.0 * i as f32), vec2(400.0, 20.0)), r.clone())).collect();
     let tm = TMap { x0: 205.0, start: 0.0, pps: 100.0 };
-    let go = |br: Rect| box_targets(comp, &rows, &hit_rows, &tm, 0.0, 20.0, 200.0, false, br);
+    let view = marquee::View { tm, top: 0.0, graph_x0: 200.0, graph_on: false };
+    // Press at `from` with the rows scrolled by `s0`, release at `to` scrolled by `s1`.
+    let drag = |from: Pos2, s0: f32, to: Pos2, s1: f32| {
+        let (paint, sel) = marquee::Anchor::press(&view, s0, from).selection(&view, s1, to);
+        marquee::targets(comp, &rows, &tm, -s1, 20.0, paint, &sel)
+    };
+    let go = |from: Pos2, to: Pos2| drag(from, 0.0, to, 0.0);
     let keyed = |ks: &[effectcraft_engine::KeyRef]| ks.iter().map(|k| k.layer.0).collect::<Vec<_>>();
     // From the outline across the boundary: layer A's row (y 0..20) and B's row, and their keys.
-    let (ls, ks) = go(Rect::from_min_max(pos2(10.0, 5.0), pos2(260.0, 65.0)));
+    let (ls, ks) = go(pos2(10.0, 5.0), pos2(260.0, 65.0));
     assert_eq!(ls, [layers[0], layers[1]]);
     assert_eq!(keyed(&ks), [layers[0], layers[1]]);
-    // The same box dragged the other way is the same rectangle: the same rows, the same keys.
-    let (ls, ks) = go(Rect::from_two_pos(pos2(260.0, 65.0), pos2(10.0, 5.0)));
+    // The same box dragged the other way: the same rows, the same keys.
+    let (ls, ks) = go(pos2(260.0, 65.0), pos2(10.0, 5.0));
     assert_eq!((ls, keyed(&ks)), (vec![layers[0], layers[1]], vec![layers[0], layers[1]]));
     // Only over the outline: rows, no keys; only over the graph: keys, and the rows crossed.
-    let (ls, ks) = go(Rect::from_min_max(pos2(10.0, 5.0), pos2(150.0, 65.0)));
+    let (ls, ks) = go(pos2(10.0, 5.0), pos2(150.0, 65.0));
     assert_eq!((ls.len(), ks.len()), (2, 0), "a key under the outline isn't touched");
     // Kept inside the time graph: keys only, no rows (a marquee over empty track area).
-    let (ls, ks) = go(Rect::from_min_max(pos2(204.0, 5.0), pos2(260.0, 65.0)));
+    let (ls, ks) = go(pos2(204.0, 5.0), pos2(260.0, 65.0));
     assert_eq!((ls.len(), keyed(&ks)), (0, vec![layers[0], layers[1]]));
     // A locked layer is not selected as a row (the engine drops its keys in keys.select).
-    let (ls, _) = go(Rect::from_min_max(pos2(10.0, 5.0), pos2(260.0, 119.0)));
+    let (ls, _) = go(pos2(10.0, 5.0), pos2(260.0, 119.0));
+    assert_eq!(ls, [layers[0], layers[1]]);
+    // Scrolled 20 pt mid-drag: the pressed corner stays on layer A's row (#2859), so A is still
+    // selected; a screen-fixed anchor would start the box below A and select only B.
+    let (ls, _) = drag(pos2(10.0, 5.0), 0.0, pos2(260.0, 45.0), 20.0);
     assert_eq!(ls, [layers[0], layers[1]]);
 }
diff --git a/crates/ui-egui/tests/it/ui_timeline_marquee.rs b/crates/ui-egui/tests/it/ui_timeline_marquee.rs
index bf6dab74e..9d72f08aa 100644
--- a/crates/ui-egui/tests/it/ui_timeline_marquee.rs
+++ b/crates/ui-egui/tests/it/ui_timeline_marquee.rs
@@ -13,9 +13,9 @@ use serde_json::json;
 const REACH: f32 = 5.5;
 
 /// A comp with one solid, its Opacity keys at 1 s and 2 s (linear) revealed.
-fn harness() -> (Harness<'static, EffectcraftApp>, u64) {
+fn harness_for(duration: f64) -> (Harness<'static, EffectcraftApp>, u64) {
     let mut s = Session::default();
-    s.execute("comp.new", json!({"name": "Box", "width": 320, "height": 180, "frameRate": 30, "duration": 4})).unwrap();
+    s.execute("comp.new", json!({"name": "Box", "width": 320, "height": 180, "frameRate": 30, "duration": duration})).unwrap();
     let id = s.execute("layer.newSolid", json!({"name": "L", "color": "#e04020", "width": 80, "height": 80})).unwrap()["layer"].as_u64().unwrap();
     for (t, v) in [(1.0, 0.0), (2.0, 100.0)] {
         s.execute("prop.addKey", json!({"layer": id, "path": "transform/opacity", "time": t, "value": v})).unwrap();
@@ -29,6 +29,10 @@ fn harness() -> (Harness<'static, EffectcraftApp>, u64) {
     (h, id)
 }
 
+fn harness() -> (Harness<'static, EffectcraftApp>, u64) {
+    harness_for(4.0)
+}
+
 /// The center of the key at `secs`: the middle of its hit rect, which is centered on the glyph.
 fn key_center(h: &Harness<'_, EffectcraftApp>, id: u64, secs: f64) -> Pos2 {
     let comp = h.state().session.active_comp().unwrap();
@@ -122,3 +126,265 @@ fn a_box_dragged_across_the_outline_and_the_graph_selects_rows_and_keys() {
     assert_eq!(keys, [1.0, 1.0]);
     assert_eq!(selected(&h), (both.clone(), both), "graph → outline");
 }
+
+/// Thirty expanded layers force row virtualization and leave room for wheel and edge scrolling.
+fn rows_harness() -> (Harness<'static, EffectcraftApp>, Vec<u64>) {
+    let mut s = Session::default();
+    s.execute("comp.new", json!({"name": "Rows", "width": 320, "height": 180, "frameRate": 30, "duration": 4})).unwrap();
+    let mut ids = vec![];
+    for i in 0..30 {
+        let id = s.execute("layer.newSolid", json!({"name": format!("Layer {i}"), "color": "#406080"})).unwrap()["layer"].as_u64().unwrap();
+        s.execute("prop.addKey", json!({"layer": id, "path": "transform/opacity", "time": 1.0, "value": 50})).unwrap();
+        ids.push(id);
+    }
+    s.execute("layer.select", json!({"layers": ids})).unwrap();
+    let mut h = Harness::builder().with_size(vec2(1600.0, 1000.0)).build_eframe(|_| EffectcraftApp::new(s));
+    h.run_steps(3);
+    let ctx = h.ctx.clone();
+    effectcraft_ui_egui::menus::invoke(h.state_mut(), &ctx, "timeline.reveal.opacity", json!({})).unwrap();
+    h.run_steps(4);
+    (h, ids)
+}
+
+/// The originally enclosed key stays in the box when wheel scrolling takes its row offscreen.
+#[test]
+fn scrolling_rows_during_a_marquee_keeps_offscreen_keys_in_the_box() {
+    let (mut h, ids) = rows_harness();
+    let top = *ids.last().unwrap();
+    let c = key_center(&h, top, 1.0);
+    let from = c - vec2(20.0, 5.0);
+    let to = c + vec2(20.0, 30.0);
+    h.event(Event::PointerMoved(from));
+    h.step();
+    h.event(Event::PointerButton { pos: from, button: egui::PointerButton::Primary, pressed: true, modifiers: Modifiers::NONE });
+    h.step();
+    h.event(Event::PointerMoved(to));
+    h.run_steps(2);
+    h.event(Event::MouseWheel {
+        unit: egui::MouseWheelUnit::Point,
+        delta: vec2(0.0, -400.0),
+        modifiers: Modifiers::NONE,
+        phase: egui::TouchPhase::Move,
+        source: egui::MouseWheelSource::Wheel,
+    });
+    h.run_steps(20);
+    assert!(h.state().ui.timeline.scroll_y > 300.0, "the real wheel handler scrolled rows");
+    h.event(Event::PointerButton { pos: to, button: egui::PointerButton::Primary, pressed: false, modifiers: Modifiers::NONE });
+    h.run_steps(2);
+    let selected: Vec<_> = h.state().session.state.selected_keys.iter().map(|k| k.layer.0).collect();
+    assert!(selected.contains(&top), "the key on layer {top} scrolled offscreen but remains inside the content-anchored marquee; actual layers {selected:?}");
+}
+
+fn press(h: &mut Harness<'_, EffectcraftApp>, from: Pos2, to: Pos2) {
+    h.event(Event::PointerMoved(from));
+    h.step();
+    h.event(Event::PointerButton { pos: from, button: egui::PointerButton::Primary, pressed: true, modifiers: Modifiers::NONE });
+    h.step();
+    h.event(Event::PointerMoved(to));
+    h.run_steps(2);
+}
+
+fn release(h: &mut Harness<'_, EffectcraftApp>, to: Pos2) {
+    h.event(Event::PointerButton { pos: to, button: egui::PointerButton::Primary, pressed: false, modifiers: Modifiers::NONE });
+    h.run_steps(2);
+}
+
+fn wheel(h: &mut Harness<'_, EffectcraftApp>, delta: Vec2) {
+    h.event(Event::MouseWheel {
+        unit: egui::MouseWheelUnit::Point,
+        delta,
+        modifiers: Modifiers::NONE,
+        phase: egui::TouchPhase::Move,
+        source: egui::MouseWheelSource::Wheel,
+    });
+    h.run_steps(20);
+}
+
+fn times(h: &Harness<'_, EffectcraftApp>) -> Vec<f64> {
+    h.state().session.state.selected_keys.iter().map(|k| k.time.seconds()).collect()
+}
+
+/// Panning time retains hidden keys while both painting and row selection respect the graph boundary.
+#[test]
+fn horizontal_scroll_keeps_hidden_keys_without_selecting_outline_layers() {
+    let (mut h, id) = harness_for(20.0);
+    h.state_mut().ui.timeline.pps = Some(200.0);
+    h.run_steps(3);
+    let c = key_center(&h, id, 1.0);
+    let to = c + vec2(20.0, 5.0);
+    press(&mut h, c - vec2(20.0, 5.0), to);
+    wheel(&mut h, vec2(-400.0, 0.0));
+    assert!(h.state().ui.timeline.start > 1.5, "time panned: {}", h.state().ui.timeline.start);
+    let graph_left = h.state().auto.find("timeline.ruler").unwrap().rect[0];
+    let box_shapes: Vec<_> =
+        h.output().shapes.iter().filter(|s| matches!(&s.shape, egui::Shape::Rect(r) if r.rect.max == to && (r.rect.height() - 10.0).abs() < 0.01)).collect();
+    assert!(!box_shapes.is_empty(), "the held marquee is drawn");
+    assert!(box_shapes.iter().all(|s| s.clip_rect.min.x >= graph_left), "a graph-only box cannot paint over the outline when its anchor scrolls out");
+    release(&mut h, to);
+    assert_eq!(times(&h), [1.0, 2.0]);
+    // Keys select their owning layer, but panning the anchor under the outline must not select
+    // unrelated layer rows. The separate cross-column test below covers those rows.
+    assert_eq!(h.state().session.state.selected_layers, [LayerId(id)]);
+}
+
+/// Returning the viewport shrinks the box again without editing the document or its history.
+#[test]
+fn shrinking_after_scrolling_removes_keys_again_and_selection_does_not_edit_the_project() {
+    let (mut h, id) = harness_for(20.0);
+    h.state_mut().ui.timeline.pps = Some(200.0);
+    h.run_steps(3);
+    let before = h.state().session.project.to_json();
+    let revision = h.state().session.revision;
+    let undo = h.state().session.history.undo.len();
+    let c = key_center(&h, id, 1.0);
+    let to = c + vec2(20.0, 5.0);
+    press(&mut h, c - vec2(20.0, 5.0), to);
+    wheel(&mut h, vec2(-400.0, 0.0));
+    wheel(&mut h, vec2(400.0, 0.0));
+    assert!(h.state().ui.timeline.start < 0.01);
+    release(&mut h, to);
+    assert_eq!(times(&h), [1.0], "shrinking is not a union of every key passed");
+    assert_eq!(h.state().session.project.to_json(), before);
+    assert_eq!(h.state().session.revision, revision);
+    assert_eq!(h.state().session.history.undo.len(), undo);
+}
+
+/// Invalidated gestures leave the prior selection intact even if the pointer keeps moving.
+#[test]
+fn cancellation_preserves_selection_and_does_not_restart_until_a_new_press() {
+    for cancel in ["escape", "ownership", "focus", "layout", "resize", "edit", "comp"] {
+        let (mut h, id) = harness();
+        h.state_mut().session.execute("keys.select", json!({"keys": [{"layer":id,"path":"transform/opacity","time":2.0}]})).unwrap();
+        h.run_steps(2);
+        let c = key_center(&h, id, 1.0);
+        let to = c + vec2(10.0, 5.0);
+        press(&mut h, c - vec2(20.0, 5.0), to);
+        assert_eq!(times(&h), [2.0], "selection commits only on release");
+        match cancel {
+            "escape" => h.event(Event::Key { key: egui::Key::Escape, physical_key: None, pressed: true, repeat: false, modifiers: Modifiers::NONE }),
+            "ownership" => h.ctx.set_dragged_id(egui::Id::unique("another-owner")),
+            "focus" => h.input_mut().focused = false,
+            "layout" => h.state_mut().ui.timeline.search = "no matching rows".into(),
+            "resize" => {
+                h.set_size(vec2(1400.0, 900.0));
+            }
+            "edit" => {
+                h.state_mut().session.execute("prop.set", json!({"layer":id,"path":"transform/opacity","value":75})).unwrap();
+            }
+            "comp" => {
+                h.state_mut().session.execute("comp.new", json!({"name":"Other"})).unwrap();
+            }
+            _ => unreachable!(),
+        }
+        h.run_steps(2);
+        let expected = times(&h);
+        h.event(Event::PointerMoved(to + vec2(1.0, 0.0)));
+        h.step();
+        release(&mut h, to);
+        assert_eq!(times(&h), expected, "{cancel} cancelled without applying the box");
+        if !matches!(cancel, "comp" | "edit") {
+            assert_eq!(times(&h), [2.0], "{cancel} preserves the prior selection");
+        }
+    }
+}
+
+/// A release-frame pointer move takes effect, modifiers add, and locked keys remain excluded.
+#[test]
+fn release_uses_the_release_position_and_additive_modifiers_and_excludes_locked_keys() {
+    for modifiers in [Modifiers::NONE, Modifiers::SHIFT, Modifiers::COMMAND] {
+        let (mut h, id) = harness();
+        h.state_mut().session.execute("keys.select", json!({"keys": [{"layer":id,"path":"transform/opacity","time":2.0}]})).unwrap();
+        h.run_steps(2);
+        let c = key_center(&h, id, 1.0);
+        press(&mut h, c - vec2(25.0, 5.0), c - vec2(15.0, 5.0));
+        h.event(Event::ModifiersChanged(modifiers));
+        h.event(Event::PointerMoved(c + vec2(10.0, 5.0)));
+        h.event(Event::PointerButton { pos: c + vec2(10.0, 5.0), button: egui::PointerButton::Primary, pressed: false, modifiers });
+        h.run_steps(2);
+        let mut actual = times(&h);
+        actual.sort_by(f64::total_cmp);
+        assert_eq!(actual, if modifiers == Modifiers::NONE { vec![1.0] } else { vec![1.0, 2.0] });
+        h.state_mut().session.execute("layer.setSwitch", json!({"layers":[id],"switch":"lock","value":true})).unwrap();
+        h.event(Event::ModifiersChanged(Modifiers::NONE));
+        h.run_steps(2);
+        assert!(marquee(&mut h, c - vec2(20.0, 5.0), c + vec2(10.0, 5.0)).is_empty(), "locked keys stay excluded");
+    }
+}
+
+/// Cross-column selection uses logical headers, including those no longer rendered after scrolling.
+#[test]
+fn crossing_into_the_outline_after_scrolling_selects_offscreen_layer_rows() {
+    let (mut h, ids) = rows_harness();
+    let c = key_center(&h, *ids.last().unwrap(), 1.0);
+    let outline = h.state().auto.find("timeline.layerMarquee").unwrap().rect;
+    let to = pos2(outline[0] + 40.0, c.y + 30.0);
+    press(&mut h, c + vec2(20.0, -5.0), to);
+    wheel(&mut h, vec2(0.0, -400.0));
+    assert!(h.state().ui.timeline.scroll_y > 300.0);
+    release(&mut h, to);
+    let selected = &h.state().session.state.selected_layers;
+    assert!(selected.contains(&LayerId(ids[ids.len() - 2])), "the second header is inside the box although it scrolled offscreen");
+    assert!(selected.len() > 5, "all intervening rows are selected");
+}
+
+/// Edge scrolling continues without pointer motion and stops as soon as the gesture is cancelled.
+#[test]
+fn a_stationary_pointer_at_either_edge_scrolls_only_until_release_or_cancel() {
+    let (mut h, ids) = rows_harness();
+    let c = key_center(&h, *ids.last().unwrap(), 1.0);
+    let area = h.state().auto.find("timeline.layerMarquee").unwrap().rect;
+    let bottom = pos2(c.x + 20.0, area[1] + area[3] - 2.0);
+    press(&mut h, c - vec2(20.0, 5.0), bottom);
+    let before = h.state().ui.timeline.scroll_y;
+    h.run_steps(30);
+    assert!(h.state().ui.timeline.scroll_y > before + 50.0, "a stationary drag requests more frames and scrolls");
+    let top = pos2(bottom.x, area[1] + 2.0);
+    h.event(Event::PointerMoved(top));
+    h.step();
+    let before = h.state().ui.timeline.scroll_y;
+    h.run_steps(10);
+    assert!(h.state().ui.timeline.scroll_y < before, "the top edge scrolls back");
+    h.event(Event::Key { key: egui::Key::Escape, physical_key: None, pressed: true, repeat: false, modifiers: Modifiers::NONE });
+    h.step();
+    let before = h.state().ui.timeline.scroll_y;
+    h.run_steps(10);
+    assert_eq!(h.state().ui.timeline.scroll_y, before, "Escape stops edge scrolling");
+    release(&mut h, top);
+    assert!(times(&h).is_empty(), "cancelled box selects nothing");
+}
+
+/// Batched wheel events cannot move the press anchor or make release query stale row positions.
+#[test]
+fn wheel_on_press_captures_the_old_anchor_and_wheel_on_release_uses_the_new_rows() {
+    for scroll_on_press in [true, false] {
+        let (mut h, ids) = rows_harness();
+        let top = *ids.last().unwrap();
+        let c = key_center(&h, top, 1.0);
+        let from = c - vec2(20.0, 5.0);
+        let to = c + vec2(20.0, 30.0);
+        if scroll_on_press {
+            h.event(Event::PointerMoved(from));
+            h.step();
+            h.event(Event::PointerButton { pos: from, button: egui::PointerButton::Primary, pressed: true, modifiers: Modifiers::NONE });
+        } else {
+            press(&mut h, from, to);
+        }
+        h.event(Event::MouseWheel {
+            unit: egui::MouseWheelUnit::Point,
+            delta: vec2(0.0, -400.0),
+            modifiers: Modifiers::NONE,
+            phase: egui::TouchPhase::Move,
+            source: egui::MouseWheelSource::Wheel,
+        });
+        if !scroll_on_press {
+            h.event(Event::PointerButton { pos: to, button: egui::PointerButton::Primary, pressed: false, modifiers: Modifiers::NONE });
+        }
+        h.step();
+        if scroll_on_press {
+            h.event(Event::PointerMoved(to));
+            h.run_steps(20);
+            release(&mut h, to);
+        }
+        assert!(h.state().session.state.selected_keys.iter().any(|k| k.layer == LayerId(top)), "scroll_on_press={scroll_on_press}");
+    }
+}