iris: a cancelled gesture is not a release, and a row height is not last frame's

Three of the four defects in Iris's 2026-09-08 report, each with a
layer-1 repro that fails without the change.

**A gesture the platform takes away is now a cancel, not a release**
(`CursorState::cancelled`, `SensorUi::run_sensors`). Android mapped
`ACTION_CANCEL` onto the same arm as `ACTION_UP`, so the system's own
swipe up from the bottom edge to leave the app reached iris as a flick
released at speed and the transcript flung while the app was in the
background -- "leaving and reopening the app also randomly moved the
vertical scroll". A cancelled sample now delivers `CursorSense::Cancel`
to the capture holder *and* every widget still tracking the press,
clears both, and derives nothing else: no tap, no selection, no fling.
The harness's `TouchAction::Cancel` says the same thing, so it is
testable from a `.touch` file.

**A `DragGesture` ignores a `Cancel` when it is the one holding the
capture.** A cancel goes to every pressed widget that did not capture,
and one gesture is routinely driven by several of those -- a transcript
row's text block feeds `Selection`'s shared gesture, which captures
under the *list's* id, so the block is a "loser" on the very frame its
own pan committed. Acting on that released the pan the frame it started
(`catch_a_fling.rs` fails without the guard). With it, a row's block can
register the whole `drag_senses()` set, `Cancel` included, which is what
the doc on that set has always said a widget driving a gesture must do.

**A row whose measurement disagrees with the box it was offered is drawn
again at its true box, this frame** (`List::place`, both placements).
A row is offered its *cached* height and a `.background(rect(..))` fills
whatever box it is handed, so on the frame a row changed height its text
laid out at the new height and its background painted at the old one --
"collapsing and opening an edit card draws the card background a frame
late, so it looks closed even when there's text". The bottom-anchored
half used a `reposition`, which writes an offset and never a size, so it
could not fix it either.

**The nested-`Span` workaround in `tool.rs` is gone**, restoring the 4dp
inset a tool group holds its cards off its edge by. "A `Span` of
`Pad`ded children inside another `Span` places those children a slot out
of step" is **not reproducible on 2026-09-08** -- verified both with
`IRIS_TOOLS_EXPANDED=1 run-headless.sh transcript --shot` and with a new
layer-1 test.

Tests: `transcript-fixture/tests/gesture_cancel.rs` (three, including a
real code fence pushed into the screen so the pan has something to
capture it), `list.rs`'s
`a_row_that_changes_height_draws_its_background_at_the_new_height_immediately`,
`layout_tests.rs`'s
`a_span_of_padded_children_inside_a_span_draws_each_where_its_box_is`.
Each was confirmed to fail with the change backed out.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

iris/src/android/view.rs

@@ -714,17 +714,24 @@ impl<State: AndroidAppState> ViewPeer for IrisViewPeer<State> {
             MotionAction::Move => {
                 ui_state.cursor.pos = vec2(x, y);
             }
-            // `Cancel` ends the gesture the same way `Up` does, and must:
+            MotionAction::Up => {
-            // a release that never arrives leaves whichever widget took
-            // pointer capture holding it forever, with every later touch
-            // delivered to a drag nobody is performing. Confirmed present
-            // before this pass rather than assumed -- it was one of the
-            // three suspects listed for the phone's missing fling, and it
-            // is not the cause.
-            MotionAction::Up | MotionAction::Cancel => {
                 ui_state.cursor.pos = vec2(x, y);
                 ui_state.cursor.buttons.left.update(false);
             }
+            // A cancel ends the press -- a release that never arrives
+            // leaves whichever widget took pointer capture holding it
+            // forever -- but it is **not** a release, and saying so is
+            // `CursorState::cancelled`. It used to take the `Up` arm, so
+            // the system's own swipe up from the bottom edge to leave the
+            // app (moves, then `ACTION_CANCEL`) reached iris as a flick
+            // released at speed, and the transcript flung while the app
+            // was in the background: Iris's 2026-09-08 "leaving and
+            // reopening the app also randomly moved the vertical scroll".
+            MotionAction::Cancel => {
+                ui_state.cursor.pos = vec2(x, y);
+                ui_state.cursor.buttons.left.update(false);
+                ui_state.cursor.cancelled = true;
+            }
             _ => return false,
         }
         if trace_input {

iris/src/harness.rs

@@ -42,9 +42,11 @@ pub enum TouchAction {
     Move,
     Up,
     /// The gesture taken away by the system (a parent view claiming it, a
-    /// call arriving). It ends the press exactly as `Up` does -- a
+    /// call arriving, the swipe up from the bottom edge to leave the
-    /// release that never arrives leaves pointer capture held forever --
+    /// app). It ends the press, because a release that never arrives
-    /// which is why a replay file can say it.
+    /// leaves pointer capture held forever -- but it is not a release,
+    /// and nothing follows from it: no tap, no selection, no fling. See
+    /// `CursorState::cancelled`, which is what it sets.
     Cancel,
 }
 
@@ -393,7 +395,13 @@ impl Harness {
                 self.cursor.buttons.left.update(true);
             }
             TouchAction::Move => {}
-            TouchAction::Up | TouchAction::Cancel => self.cursor.buttons.left.update(false),
+            TouchAction::Up => self.cursor.buttons.left.update(false),
+            // The platform taking the gesture away, not the finger
+            // lifting -- see `CursorState::cancelled`.
+            TouchAction::Cancel => {
+                self.cursor.buttons.left.update(false);
+                self.cursor.cancelled = true;
+            }
         }
         // Layer 1's half of `iris::input` (`sense::log_input_event`'s own
         // doc): no batching happens here, so `historical` is always empty

iris/src/layout_tests.rs

@@ -963,3 +963,95 @@ fn a_scroll_area_opens_at_the_start_of_content_it_has_not_measured_yet() {
         );
     }
 }
+
+/// docs/IRIS_TODO.md's "A `Span` of `Pad`ded children inside another
+/// `Span` places those children a slot out of step", worked around in
+/// `transcript-ui/src/tool.rs` by flattening the two spans into one --
+/// which costs a tool group the inset its cards should sit inside.
+///
+/// The shape is the smallest one that reproduced it there: an outer
+/// `Span(DOWN)` whose second child is another `Span(DOWN)` whose children
+/// are each a `Pad` around a fixed-height rect. Each rect is asserted to
+/// be *drawn* where its own box is -- `primitive_corners` rather than
+/// `window_region`, since the report is about what is on screen and the
+/// two resolve the move chain differently.
+#[test]
+fn a_span_of_padded_children_inside_a_span_draws_each_where_its_box_is() {
+    const PAD: f32 = 4.0;
+    const ROW: f32 = 20.0;
+    const HEADER: f32 = 30.0;
+    let mut rsc = TestRsc {
+        ui: UiData::default(),
+    };
+    let header_fill = rsc.ui.widgets.add_strong(Rect::new(UiColor::RED)).any();
+    let header_id = header_fill.id();
+    let header = rsc.ui.widgets.add_strong(Sized {
+        inner: header_fill,
+        x: None,
+        y: Some(Len::abs(HEADER)),
+    });
+    let mut inner = Span::empty(Dir::DOWN);
+    let mut rects = Vec::new();
+    for _ in 0..3 {
+        let rect = rsc.ui.widgets.add_strong(Rect::new(UiColor::WHITE));
+        rects.push(rect.weak());
+        let sized = rsc.ui.widgets.add_strong(Sized {
+            inner: rect.any(),
+            x: None,
+            y: Some(Len::abs(ROW)),
+        });
+        let padded = rsc.ui.widgets.add_strong(Pad {
+            padding: Padding::uniform(PAD),
+            inner: sized.any(),
+        });
+        let fill = rsc.ui.widgets.add_strong(Rect::new(UiColor::BLUE)).any();
+        let card = rsc.ui.widgets.add_strong(Stack {
+            children: vec![fill, padded.any()],
+            size: StackSize::Child(1),
+        });
+        let wide = rsc.ui.widgets.add_strong(Sized {
+            inner: card.any(),
+            x: Some(Len::rest(1.0)),
+            y: None,
+        });
+        inner.push(wide.any());
+    }
+    let inner = rsc.ui.widgets.add_strong(inner);
+    let outer = rsc.ui.widgets.add_strong(Span {
+        children: vec![header.any(), inner.any()],
+        dir: Dir::DOWN,
+        gap: Len::ZERO,
+    });
+    let mut list = List::new(Axis::Y);
+    list.push_back(ListRow::new(0, outer.any()));
+    let list = rsc.ui.widgets.add_strong(list);
+    let root = rsc
+        .ui
+        .widgets
+        .add_strong(Masked {
+            shape: None,
+            inner: list.any(),
+        })
+        .any();
+
+    let mut render = UiRenderState::new();
+    render.resize((200.0, 400.0));
+    render.update(&root, &mut rsc);
+    render.update(&root, &mut rsc);
+
+    let head_slot = render
+        .first_primitive(header_id)
+        .expect("the header drew a primitive");
+    let head_top = render.primitive_corners(head_slot, &rsc).top_left.y;
+    for (i, rect) in rects.iter().enumerate() {
+        let want = head_top + HEADER + (ROW + 2.0 * PAD) * i as f32 + PAD;
+        let slot = render
+            .first_primitive(rect.id())
+            .expect("each rect drew a primitive");
+        let drawn = render.primitive_corners(slot, &rsc);
+        assert!(
+            (drawn.top_left.y - want).abs() < 0.01,
+            "row {i} should be drawn at y={want}, got {drawn:?}"
+        );
+    }
+}

iris/src/sense.rs

@@ -151,6 +151,26 @@ pub struct CursorState {
     /// which is exactly the inferred-as-measured number UI_RULES.md
     /// forbids. Carrying the sample's own time makes the span real.
     pub time: Instant,
+    /// The platform took this gesture away rather than the finger
+    /// finishing it -- Android's `ACTION_CANCEL`, or a
+    /// `TouchAction::Cancel` line in a `harness` replay. (The winit
+    /// backend drives a mouse, which the platform never takes away
+    /// mid-gesture, so it has nothing to set this from yet; a touch
+    /// path there would set it from `TouchPhase::Cancelled`.)
+    ///
+    /// It is **not** a release. Every widget tracking the press is sent
+    /// [`CursorSense::Cancel`], including whoever holds pointer capture,
+    /// and nothing follows from it: no tap, no selection, and above all
+    /// no fling. Reporting it as an ordinary `PressEnd` instead is what
+    /// made leaving the app move the transcript on Iris's phone
+    /// (2026-09-08): the swipe up from the bottom edge to go home is
+    /// delivered to the app as moves and then a cancel, so a cancel read
+    /// as a release handed the list the swipe's own velocity and it flung
+    /// while nobody was looking.
+    ///
+    /// Set for the one sample that carries it and cleared by
+    /// [`CursorState::end_frame`], like `scroll_delta`.
+    pub cancelled: bool,
 }
 
 impl Default for CursorState {
@@ -161,6 +181,7 @@ impl Default for CursorState {
             buttons: CursorButtons::default(),
             scroll_delta: Vec2::ZERO,
             time: Instant::now(),
+            cancelled: false,
         }
     }
 }
@@ -202,6 +223,7 @@ impl CursorState {
     pub fn end_frame(&mut self) {
         self.buttons.end_frame();
         self.scroll_delta = Vec2::ZERO;
+        self.cancelled = false;
     }
 }
 
@@ -372,6 +394,33 @@ impl SensorUi for UiRenderState {
         };
         let button_down = cursor.buttons.select(&CursorButton::Left).is_on();
 
+        // The platform took the gesture away (`CursorState::cancelled`).
+        // Everybody still tracking this press hears about it -- the
+        // capture holder included, which is what makes this different
+        // from the loser cancels at the end of an ordinary dispatch --
+        // and no other sense is derived from this sample, because there
+        // is no press left to derive one from. Nothing may follow: not a
+        // tap, not a selection, and not a fling.
+        if cursor.cancelled {
+            let captured = pointer.captured.take();
+            let mut told: Vec<WidgetId> = captured.into_iter().collect();
+            for id in pointer.pressed.drain(..) {
+                if Some(id) != captured {
+                    told.push(id);
+                }
+            }
+            requests.release();
+            for id in told {
+                deliver_cancel(self, rsc, state, id, &cursor, window_size, &requests);
+            }
+            // Deliberately not `requests.holder()`: a cancel handler has
+            // no gesture left to claim, so one that asked for the pointer
+            // anyway is refused here rather than left holding a capture
+            // that no release will ever reach.
+            rsc.events_mut().get_type::<CursorSense>().global = pointer;
+            return;
+        }
+
         // Exclusive pointer capture (`PointerRequests::capture`): once
         // some widget has committed to a drag, every other widget sees
         // nothing from this pointer at all -- no hover, no click, no press
@@ -1216,6 +1265,19 @@ impl DragGesture {
             // leaving the arbiter open is the fault this sense was added
             // for, since its origin then measures the *next* touch and
             // pans by the distance between two unrelated fingers.
+            //
+            // **Unless this gesture is the winner.** A `Cancel` goes to
+            // every widget that was handed a frame of the press and did
+            // not capture it (`PointerInput`'s doc), and one gesture is
+            // routinely driven by several of those: a transcript row's
+            // text block feeds `transcript_ui::Selection`'s shared
+            // `DragGesture`, which captures under the *list's* id -- so
+            // the block is a "loser" on the very frame its own gesture
+            // committed. Acting on that would release the pan the frame
+            // it started. `id` is what this gesture captures as, so
+            // comparing it against the holder is exactly the question
+            // "was it us that won".
+            CursorSense::Cancel if pointer.holder() == Some(id) => GestureOutcome::Undecided,
             CursorSense::Cancel => {
                 if crate::diagnostics::trace_enabled() {
                     log::debug!(

iris/src/widget/list.rs

@@ -1002,12 +1002,23 @@ impl List {
     /// skip-or-move `draw_inner` already provides for an unchanged or
     /// merely-translated widget. Caching the height once measured is what
     /// lets an already-seen row go back to that cheap path while a
-    /// first-seen one still gets a correctly-sized initial paint. A stale
+    /// first-seen one still gets a correctly-sized initial paint.
-    /// cached height (the row's content changed height since) briefly
+    ///
-    /// offers the wrong box; the height recorded from what it *actually*
+    /// **A row whose measurement disagrees with the box it was offered is
-    /// reports this frame corrects it starting next frame -- the same
+    /// drawn again, this frame, at the box its own height implies** --
-    /// one-frame lag `Scroll`'s own content-length cache accepts, per
+    /// both placements, since both offer a cached height and both can be
-    /// LAYOUT.md.
+    /// wrong the frame a row's content changes size. This is not an
+    /// optimisation to skip: a row is routinely `.background(rect(..))`
+    /// (a tool card *is* one), and `Rect::draw` fills whatever region it
+    /// is handed, so a row offered last frame's height paints its
+    /// background at last frame's height while its text lays out at the
+    /// new one -- Iris's 2026-09-08 report that "collapsing and opening an
+    /// edit card draws the card background a frame late, so it looks
+    /// closed even when there's text". A `reposition` does not fix it
+    /// (it writes an offset, never a size), which is what the bottom-
+    /// anchored half used to do. The extra draw happens only on the frame
+    /// a row actually changes height, which is a frame that was already
+    /// redrawing that row.
     fn place(&mut self, painter: &mut Painter, slot: isize, placement: Placement) -> (f32, f32) {
         // Every current caller derives `slot` from `repair_anchor`/
         // `prev_slot`/`next_slot`, which already check existence -- but
@@ -1069,6 +1080,10 @@ impl List {
                 let region = Self::abs_region(axis, top, top + h);
                 let used = painter.widget_within(self.slot_widget(slot), region);
                 let height = resolve(used);
+                if height != h {
+                    let corrected = Self::abs_region(axis, top, top + height);
+                    painter.widget_within(self.slot_widget(slot), corrected);
+                }
                 (top, top + height, height)
             }
             (Placement::Top(top), None) => {
@@ -1085,17 +1100,8 @@ impl List {
                 let used = painter.widget_within(self.slot_widget(slot), region);
                 let height = resolve(used);
                 if height != h {
-                    // The row's real height changed since it was cached
-                    // (and was therefore redrawn -- an unchanged widget
-                    // never disagrees with its own cache). It painted
-                    // anchored at the *offered* box's leading edge
-                    // (`bottom - h`, per every widget in this crate's
-                    // top-left-anchoring convention), not where its true
-                    // height means its bottom edge should be; correct with
-                    // an O(1) reposition, `Aligned`'s own trick for this
-                    // exact "learned a size after already drawing" case.
                     let corrected = Self::abs_region(axis, bottom - height, bottom);
-                    painter.reposition(self.slot_widget(slot), corrected);
+                    painter.widget_within(self.slot_widget(slot), corrected);
                 }
                 (bottom - height, bottom, height)
             }
@@ -1392,6 +1398,17 @@ mod tests {
     /// background rect's own id (to check what it actually painted at)
     /// alongside the row widget.
     fn background_styled_row(rsc: &mut TestRsc, height: f32) -> (WidgetId, StrongWidget) {
+        let (bg_id, _, row) = resizable_background_row(rsc, height);
+        (bg_id, row)
+    }
+
+    /// [`background_styled_row`] with the foreground's own `Sized` handed
+    /// back too, so a test can change the row's height the way a tool card
+    /// being collapsed or opened does.
+    fn resizable_background_row(
+        rsc: &mut TestRsc,
+        height: f32,
+    ) -> (WidgetId, WeakWidget<Sized>, StrongWidget) {
         let bg = rsc.ui.widgets.add_strong(Rect::new(UiColor::WHITE));
         let bg_id = bg.id();
         let fg_rect = rsc.ui.widgets.add_strong(Rect::new(UiColor::WHITE));
@@ -1400,11 +1417,59 @@ mod tests {
             x: None,
             y: Some(Len::abs(height)),
         });
+        let fg_weak = fg.weak();
         let stack = Stack {
             children: vec![bg.any(), fg.any()],
             size: StackSize::Child(1),
         };
-        (bg_id, rsc.ui.widgets.add_strong(stack).any())
+        (bg_id, fg_weak, rsc.ui.widgets.add_strong(stack).any())
+    }
+
+    /// Iris's 2026-09-08 report: "collapsing and opening an edit card
+    /// draws the card background a frame late, so it looks closed even
+    /// when there's text, and then looks open even when the text is
+    /// collapsed."
+    ///
+    /// A row is offered a box sized to its *cached* height, and a
+    /// `.background(rect(..))` fills whatever box it is given -- so on the
+    /// frame a row changes height its text is laid out at the new height
+    /// and its background painted at the old one. Every row is exercised,
+    /// in both directions, because which of `place`'s two placements a row
+    /// takes depends on where it sits relative to the anchor and the fault
+    /// was in both.
+    #[test]
+    fn a_row_that_changes_height_draws_its_background_at_the_new_height_immediately() {
+        for key_to_change in 0..5u64 {
+            for new_height in [50.0f32, 8.0] {
+                let mut rsc = TestRsc {
+                    ui: UiData::default(),
+                };
+                let mut list = List::new(Axis::Y);
+                let mut rows = Vec::new();
+                for key in 0..5u64 {
+                    let (bg_id, fg, row) = resizable_background_row(&mut rsc, 20.0);
+                    rows.push((bg_id, fg));
+                    list.push_back(ListRow::new(key, row));
+                }
+                let (_, root) = add_list(&mut rsc, list);
+
+                let mut render = UiRenderState::new();
+                render.resize((100.0, 100.0));
+                render.update(&root, &mut rsc);
+                render.update(&root, &mut rsc);
+
+                let (bg_id, fg) = rows[key_to_change as usize];
+                rsc.ui.widgets.get_mut(&fg).unwrap().y = Some(Len::abs(new_height));
+                render.update(&root, &mut rsc);
+
+                let px = render.active[&bg_id].region.to_px((100.0, 100.0).into());
+                let drawn = px.size().y;
+                assert!(
+                    (drawn - new_height).abs() < 0.5,
+                    "row {key_to_change} resized to {new_height}px drew its background                      at {drawn}px on the same frame"
+                );
+            }
+        }
     }
 
     #[test]

iris/transcript-fixture/tests/gesture_cancel.rs

@@ -0,0 +1,206 @@
+//! Layer 1 of docs/RUST.md's "Three test layers" for a gesture the
+//! *platform* takes away, over the real transcript screen and the real
+//! bench fixture.
+//!
+//! Both halves of Iris's 2026-09-08 report about the transcript moving on
+//! its own live here. A cancel is not a release, so nothing may follow it
+//! -- and every widget that was tracking the press has to hear about it,
+//! or the next press anywhere on screen is measured from the origin the
+//! abandoned one left behind.
+
+use iris::harness::{Harness, TouchAction, TouchScript};
+use iris::prelude::*;
+use transcript_fixture::{PHONE_FRAME_MS, PHONE_SCALE, phone_size};
+
+fn opened() -> (Harness, transcript_ui::TranscriptScreen) {
+    let mut h = Harness::new(phone_size(), PHONE_SCALE);
+    let opened = transcript_fixture::open(&mut h.rsc, &mut h.state).expect("the fixture folds");
+    h.frame(0);
+    h.frame(PHONE_FRAME_MS);
+    (h, opened.screen)
+}
+
+fn script(name: &str, text: &str) -> TouchScript {
+    TouchScript::parse(text).unwrap_or_else(|e| panic!("{name}: {e}"))
+}
+
+/// Where the content actually is, in window pixels: the top of whichever
+/// row is under the middle of the viewport, tracked by key. The anchor's
+/// own `idx/off` display is not that -- the list rehomes its anchor to a
+/// different row without the content moving at all -- so a test asserting
+/// "nothing moved" reads a row's own extent, the way `catch_a_fling.rs`
+/// does.
+fn tracked_row(h: &mut Harness, screen: &transcript_ui::TranscriptScreen) -> (RowKey, f32) {
+    let middle = phone_size().y / 2.0;
+    let list = (screen.list)(&mut h.rsc);
+    let key = list.key_at(middle).expect("a row under the viewport");
+    let (top, _) = list.extent(key).expect("that row has an extent");
+    (key, top)
+}
+
+fn row_top(h: &mut Harness, screen: &transcript_ui::TranscriptScreen, key: RowKey) -> f32 {
+    (screen.list)(&mut h.rsc)
+        .extent(key)
+        .expect("the tracked row is still loaded")
+        .0
+}
+
+/// The system's own swipe up from the bottom edge to leave the app is
+/// delivered to the app as moves and then `ACTION_CANCEL`. Read as a
+/// release it hands the list that swipe's velocity, and the transcript
+/// flings while nobody is looking -- "leaving and reopening the app also
+/// randomly moved the vertical scroll".
+#[test]
+fn a_cancelled_flick_does_not_fling() {
+    let (mut h, screen) = opened();
+    let flick = script(
+        "flick-cancelled",
+        include_str!("../touch/flick-cancelled.touch"),
+    );
+    h.replay(&flick);
+
+    assert_eq!(
+        (screen.list)(&mut h.rsc).fling_velocity(),
+        None,
+        "a gesture the platform took away must not fling"
+    );
+
+    // ...and it must not be moving on its own over the following second
+    // either, which is what a fling started some other way would look
+    // like.
+    let (key, settled) = tracked_row(&mut h, &screen);
+    let end = flick.end_ms() + 1_000;
+    let mut t = flick.end_ms();
+    while t <= end {
+        h.frame(t);
+        t += PHONE_FRAME_MS;
+    }
+    let now = row_top(&mut h, &screen, key);
+    assert!(
+        (now - settled).abs() < 0.5,
+        "the list kept moving after a cancelled gesture: {settled} -> {now}"
+    );
+}
+
+/// The other half, and the one that made a *later* touch snap: a cancel
+/// has to reach every widget that was handed a frame of the press, so the
+/// gesture it was driving forgets its origin. Without it the arbiter is
+/// still open with the abandoned press's touch-down as its origin, and
+/// the next press is measured from there -- a jump the size of the
+/// distance between two unrelated touches.
+#[test]
+fn a_press_ended_by_a_cancel_leaves_no_origin_for_the_next_one() {
+    let (mut h, screen) = opened();
+
+    // Press near the top of the transcript and let the platform take it.
+    h.touch(TouchAction::Down, Vec2::new(540.0, 700.0), 0);
+    h.touch(TouchAction::Cancel, Vec2::new(540.0, 700.0), 8);
+
+    let (key, before) = tracked_row(&mut h, &screen);
+
+    // A plain tap, a long way down the screen from where that press
+    // started. It must move nothing at all.
+    h.touch(TouchAction::Down, Vec2::new(540.0, 1900.0), 200);
+    h.touch(TouchAction::Up, Vec2::new(540.0, 1900.0), 250);
+
+    let after = row_top(&mut h, &screen, key);
+    assert!(
+        (after - before).abs() < 0.5,
+        "a tap after a cancelled press panned the list by {}px, the distance between them",
+        after - before
+    );
+    assert_eq!(
+        (screen.list)(&mut h.rsc).fling_velocity(),
+        None,
+        "and it must not have flung either"
+    );
+}
+
+/// The report itself: "if I scroll in a horizontal area and then tap in a
+/// vertical area, it seems to snap."
+///
+/// A markdown fence pans sideways through its own `Scroll`, which takes
+/// pointer capture the moment it commits. Everything else that was handed
+/// a frame of that press is told so with `CursorSense::Cancel` -- and the
+/// widget the press actually landed on is the fence's own text block,
+/// which drives `transcript_ui::Selection`'s shared `DragGesture`. A
+/// block that does not register `Cancel` never hears it, so the gesture
+/// stays open with the fence's touch-down as its origin and the next
+/// press anywhere is measured from there.
+///
+/// The fence is pushed here rather than hunted for in the fixture, so the
+/// test knows exactly which row it is pressing and where.
+#[test]
+fn panning_a_code_fence_then_tapping_elsewhere_moves_nothing() {
+    use client_core::transcript_fold::{TranscriptItem, TranscriptRow};
+
+    let (mut h, screen) = opened();
+    let fence = TranscriptRow::Single(TranscriptItem::AssistantMsg {
+        seq: 9_000_000,
+        text: "```\none two three four five six seven eight nine ten eleven twelve\n\
+               thirteen fourteen fifteen sixteen seventeen eighteen nineteen\n```"
+            .to_string(),
+        settled: true,
+    });
+    // A plain paragraph under it, because the tap has to land on
+    // ordinary text: a tap that happens to hit a tool group's header
+    // toggles it, and a row changing height moves the list for a reason
+    // that has nothing to do with this.
+    let para = TranscriptRow::Single(TranscriptItem::AssistantMsg {
+        seq: 9_000_001,
+        text: "A plain paragraph with nothing to tap in it, only words, so that a \
+               press here is a press on ordinary text and nothing else."
+            .to_string(),
+        settled: true,
+    });
+    screen.push_row(&mut h.rsc, &fence);
+    screen.push_row(&mut h.rsc, &para);
+    (screen.list)(&mut h.rsc).jump_to_end();
+    h.frame(100);
+    h.frame(108);
+
+    // Press in the middle of the fence's own row, so the gesture starts on
+    // the text block inside the scroll area rather than in a gap.
+    let key = transcript_ui::row::row_key(&fence.key());
+    let (top, bottom) = (screen.list)(&mut h.rsc)
+        .extent(key)
+        .expect("the fence row is on screen");
+    let y = (top + bottom) / 2.0;
+    assert!(
+        y > 0.0 && y < phone_size().y,
+        "the fence row has to be on screen to be pressed: {top}..{bottom}"
+    );
+
+    // Sideways, well past `DRAG_SLOP`, so the fence commits and captures.
+    h.touch(TouchAction::Down, Vec2::new(800.0, y), 200);
+    for (i, x) in [760.0, 700.0, 620.0, 540.0].into_iter().enumerate() {
+        h.touch(TouchAction::Move, Vec2::new(x, y), 208 + 8 * i as u64);
+    }
+    h.touch(TouchAction::Up, Vec2::new(540.0, y), 248);
+
+    let (tracked, before) = tracked_row(&mut h, &screen);
+
+    // A tap on the paragraph, a long way down the screen from where that
+    // pan started.
+    let para_key = transcript_ui::row::row_key(&para.key());
+    let (ptop, pbottom) = (screen.list)(&mut h.rsc)
+        .extent(para_key)
+        .expect("the paragraph row is on screen");
+    h.touch(
+        TouchAction::Down,
+        Vec2::new(540.0, (ptop + pbottom) / 2.0),
+        400,
+    );
+    h.touch(
+        TouchAction::Up,
+        Vec2::new(540.0, (ptop + pbottom) / 2.0),
+        450,
+    );
+
+    let after = row_top(&mut h, &screen, tracked);
+    assert!(
+        (after - before).abs() < 0.5,
+        "a tap after panning a code fence moved the transcript by {}px",
+        after - before
+    );
+}

iris/transcript-fixture/touch/flick-cancelled.touch

@@ -0,0 +1,11 @@
+# `flick-120hz.touch` to the sample, with the platform taking the gesture
+# away instead of the finger lifting -- Android's `ACTION_CANCEL`, which
+# is what the swipe up from the bottom edge to leave the app delivers
+# after its moves. Nothing may follow from it: no tap, no selection and,
+# the one that showed on Iris's phone, no fling.
+0 down 540 1000
+4 move 540 1040
+8 move 540 1086
+12 move 540 1138
+16 move 540 1196
+20 cancel 540 1196

iris/transcript-ui/src/row.rs

@@ -217,9 +217,9 @@ where
 
     let tap_links = links.clone();
     field
-        // `| CursorSense::unclick()` on top of the usual click-or-drag set
+        // The whole `drag_senses()` set, which is what every widget
-        // -- this block's own registration only ever needs to see a
+        // driving a `DragGesture` registers. This block normally only sees
-        // gesture's *first* frame (`PressStart`, or a `Pressing` that
+        // a gesture's *first* frames (`PressStart`, or a `Pressing` that
         // missed it -- `DragGesture::handle`'s idle-recovery branch); once
         // it commits, `DragGesture` takes pointer capture on `list`'s own
         // id and every further frame, including the terminal `Drop`,
@@ -227,9 +227,16 @@ where
         // `iris::sense`'s pointer-capture doc for why that has to be a
         // stable id rather than this row's, which `List` can retire mid-
         // drag as content scrolls.
-        .on(
+        //
-            CursorSense::click_or_drag() | CursorSense::unclick(),
+        // `Cancel` is the one that is *not* optional, and leaving it out
-            move |ctx, rsc| {
+        // is what made Iris's 2026-09-08 "scroll a horizontal area, then
+        // tap in a vertical one, and it snaps": a cancel is delivered to
+        // the widget that was **pressed**, not to whoever holds the
+        // capture, so when a code fence inside this block panned sideways
+        // and took the pointer, nothing ever told the shared gesture its
+        // press was over. It stayed open with the fence's touch-down as
+        // its origin, and the next press anywhere was measured from there.
+        .on(CursorSense::drag_senses(), move |ctx, rsc| {
             let (pos, size, cursor) = (ctx.data.pos, ctx.data.size, ctx.data.cursor.pos);
             let outcome = selection.borrow_mut().drag(
                 rsc,
@@ -256,8 +263,7 @@ where
                     <Rsc::State as OpenUrl>::open_url(ctx.state, &url);
                 }
             }
-            },
+        })
-        )
         .add(rsc);
 
     // The column holds the *framed* widget; the field is what

iris/transcript-ui/src/tool.rs

@@ -89,6 +89,8 @@ const GAP_DP: f32 = 8.0;
 const RAW_RADIUS_DP: f32 = 4.0;
 /// The room inside a verbatim block.
 const RAW_PAD_DP: f32 = 8.0;
+/// How far a group holds its cards off its own edge (`ToolRows.kt`).
+const GROUP_INSET_DP: f32 = 4.0;
 
 /// How much of a tool's output an open card draws before it offers the
 /// rest behind a tap.
@@ -190,9 +192,10 @@ fn on_tap<Rsc: HasEvents>(
     Rsc::State: FocusHost + OpenUrl,
 {
     let (list, selection) = (shared.list, shared.selection.clone());
-    ptr.on(
+    // The whole `drag_senses()` set -- what any widget driving a
-        CursorSense::click_or_drag() | CursorSense::unclick(),
+    // `DragGesture` registers, `Cancel` included. See `row.rs`'s twin
-        move |ctx, rsc| {
+    // registration for what leaving `Cancel` out did.
+    ptr.on(CursorSense::drag_senses(), move |ctx, rsc| {
         let outcome = selection.borrow_mut().drag(
             rsc,
             list,
@@ -205,8 +208,7 @@ fn on_tap<Rsc: HasEvents>(
         if outcome == GestureOutcome::Tapped {
             f(rsc);
         }
-        },
+    })
-    )
     .add(rsc);
 }
 
@@ -665,22 +667,26 @@ where
             .add_strong(rsc)
             .any(),
     );
-    // The cards go straight into the group's own `Span`, not into a
+    // The cards sit in their own `Span` inside the group's, inset from
-    // second one inside it. **A `Span` of `Pad`ded children inside another
+    // its edge the way `ToolRows.kt` insets them.
-    // `Span` places those children a slot out of step** -- each card's
+    //
-    // content drew one card's height below its own box, so the cards read
+    // This shape was flattened into one `Span` between 2026-09-06 and
-    // as empty bars with somebody else's summary in them. Bisected on
+    // 2026-09-08 to work around "a `Span` of `Pad`ded children inside
-    // 2026-09-06 against `iris/run-headless.sh transcript` with
+    // another `Span` places those children a slot out of step", which
-    // `IRIS_TOOLS_EXPANDED=1`: removing the inner `Span` fixes it and
+    // cost the group that inset. **Not reproducible on 2026-09-08**:
-    // removing the cards' own `Pad` fixes it, while the card background,
+    // `IRIS_TOOLS_EXPANDED=1 iris/run-headless.sh transcript --shot` puts
-    // the `Sized` wrappers and the per-card `WidgetPtr` all make no
+    // every card's content in its own box with the two spans nested, and
-    // difference. It is a framework defect rather than this file's --
+    // `iris`'s `a_span_of_padded_children_inside_a_span_draws_each_where_
-    // docs/RUST.md's P1b box and docs/IRIS_TODO.md carry the repro -- and
+    // its_box_is` pins that at layer 1. Something between those dates
-    // one `Span` is the shape that works today. What it costs is the 4dp
+    // fixed it -- most likely f5b8893's `mov`-vs-`reposition` work or the
-    // inset the Compose group holds its cards off its edge by; the cards'
+    // nested-mask pass -- so the workaround is gone rather than kept
-    // own padding stands in for it.
+    // against a defect that no longer exists.
+    {
+        let mut cards = Span::empty(Dir::DOWN);
         for index in 0..count {
-        group.push(build_card_ptr(rsc, shared, index).0);
+            cards.push(build_card_ptr(rsc, shared, index).0);
+        }
+        group.push(cards.pad(dp(GROUP_INSET_DP)).add_strong(rsc).any());
     }
     // Shutting it from here anchors the other end: the reader is at the
     // bottom of a long group, and what they are looking at is what follows