Room list: fix scrolling with touch device (#34381)

* Fix touchscreen scroll room list

* Add unit tests

packages/shared-components/src/room-list/VirtualizedRoomListView/VirtualizedRoomListView.test.tsx

@@ -197,6 +197,54 @@ describe("<VirtualizedRoomListView />", () => {
         });
     });
 
+    describe("pointer drag activation", () => {
+        beforeEach(() => {
+            (Sections.args.changeRoomSection as any).mockClear?.();
+        });
+
+        it("does not start a drag when a finger moves (touch scrolling the list)", async () => {
+            // For touch, dragging only activates after a 250ms hold; moving the finger first aborts
+            // it so the list scrolls instead of dragging a room. Simulate a finger press that moves
+            // immediately (as when scrolling) and assert no drag ever starts.
+            const user = userEvent.setup();
+            renderWithMockContext(<Sections />);
+
+            const status = screen.getByRole("status");
+            const roomButton = await screen.findByRole("button", { name: "Open room General" });
+
+            await user.pointer([
+                { keys: "[TouchA>]", target: roomButton, coords: { x: 20, y: 20 } },
+                { pointerName: "TouchA", coords: { x: 20, y: 140 } },
+                { keys: "[/TouchA]" },
+            ]);
+
+            expect(status).toHaveTextContent("");
+            expect(Sections.args.changeRoomSection).not.toHaveBeenCalled();
+        });
+
+        it("starts a drag when the mouse moves past the activation distance", async () => {
+            // For mouse, dragging activates as soon as the pointer moves past 5px, so the same
+            // press-and-move gesture that scrolls on touch drags the room into another section.
+            const user = userEvent.setup();
+            renderWithMockContext(<Sections />);
+
+            const status = screen.getByRole("status");
+            const roomButton = await screen.findByRole("button", { name: "Open room General" });
+
+            await user.pointer([
+                { keys: "[MouseLeft>]", target: roomButton, coords: { x: 20, y: 20 } },
+                { coords: { x: 20, y: 140 } },
+            ]);
+
+            // The drag has activated: the live region reflects the ongoing drag.
+            await waitFor(() => expect(status).toHaveTextContent("General"));
+
+            await user.pointer({ keys: "[/MouseLeft]" }); // release to drop
+
+            await waitFor(() => expect(Sections.args.changeRoomSection).toHaveBeenCalled());
+        });
+    });
+
     describe("scrollToSectionTag", () => {
         it("skips scroll when scrollToSectionTag does not match any section", () => {
             const roomListState = {

packages/shared-components/src/room-list/VirtualizedRoomListView/VirtualizedRoomListView.tsx

@@ -600,10 +600,17 @@ export function VirtualizedRoomListView({ vm, renderAvatar, onKeyDown }: Virtual
                 }
             }}
             sensors={[
-                // By default, the PointerSensor activates dragging immediately on pointer down, which interferes with keyboard navigation.
+                // By default, PointerSensor activates dragging immediately on mouse pointer down, which interferes
-                // So we start dragging after the pointer has moved by 5 pixels, to allow for click without dragging
+                // with clicking a room and keyboard navigation, so for mouse/pen we require a small drag distance
+                // before a drag starts (allowing a plain click without dragging).
+                // For touch, a Delay constraint that aborts the drag if the finger moves before the delay elapses is used to avoid accidental drags when scrolling the list with a finger.
                 PointerSensor.configure({
-                    activationConstraints: [new PointerActivationConstraints.Distance({ value: 5 })],
+                    activationConstraints(event) {
+                        if (event.pointerType === "touch") {
+                            return [new PointerActivationConstraints.Delay({ value: 250, tolerance: 5 })];
+                        }
+                        return [new PointerActivationConstraints.Distance({ value: 5 })];
+                    },
                 }),
                 // By default, the KeyboardSensor uses both space and enter to start dragging, which interferes with the keyboard enter shortcut to open a room.
                 KeyboardSensor.configure({