feat: select overlay windows with the mouse cursor

Moving the cursor over an overlay row now previews that window, the
same as dragging a finger across it; sliding off every row keeps the
last preview. Clicks while the overlay is up do nothing and never
reach clients, and releasing Alt commits the preview.

tests/test_smoke.py

@@ -4962,6 +4962,91 @@ def test_overlay_touch_drag(session):
     assert session.active() == drag_target
 
 
+def test_overlay_pointer_hover(session):
+    """Moving the cursor over the overlay while Alt is held previews rows
+    like a touch drag (no click needed); motion off every row sticks to
+    the last preview; clicks are swallowed (no new selection, no active
+    change, nothing reaches the client); Alt release commits."""
+    session.wait_any_active()
+    session.wait_surface_mapped(0)
+    session.wait_surface_mapped(1)
+    session.mods(ALT)
+    try:
+        path = session.dump_host()
+        w, h, _ = session.ppm_rgb(path)
+        cx = w // 2
+        # Locate both rows by warping down the middle.
+        rows = {}
+        deadline = time.monotonic() + 25.0
+        y = 0
+        while time.monotonic() < deadline and len(rows) < 2 and y < h:
+            before = len(re.findall(r"\[pointer\] select app=", session.read_log()))
+            session.warp(cx, y)
+            time.sleep(0.18)
+            m = re.findall(r"\[pointer\] select app=(\d+)", session.read_log())
+            if len(m) > before and m[-1] not in rows:
+                rows[m[-1]] = y
+            y += 20
+        assert len(rows) == 2, f"hover sweep found rows {rows}"
+        yA, yB = sorted(rows.values())
+        # Hover from the upper row into the lower one.
+        session.warp(cx, yA)
+        time.sleep(0.3)
+        session.warp(cx, yB)
+        time.sleep(0.3)
+        sels = re.findall(r"\[pointer\] select app=(\d+)", session.read_log())
+        assert len(sels) >= 2 and sels[-2] != sels[-1], \
+            f"hover never re-targeted: {sels[-2:]}"
+        hover_target = int(sels[-1])
+        # Motion off every row keeps the last preview.
+        n0 = len(re.findall(r"\[pointer\] select app=", session.read_log()))
+        session.warp(5, 5)
+        time.sleep(0.3)
+        n1 = len(re.findall(r"\[pointer\] select app=", session.read_log()))
+        assert n1 == n0, "off-row hover changed selection"
+        # Clicks are swallowed: no selection, no active change.
+        a0 = session.active_count()
+        session.button(BTN_LEFT, 1)
+        time.sleep(0.15)
+        session.button(BTN_LEFT, 0)
+        time.sleep(0.3)
+        n2 = len(re.findall(r"\[pointer\] select app=", session.read_log()))
+        assert n2 == n1, "click while overlay up selected a window"
+        assert session.active_count() == a0, "click while overlay up moved focus"
+        assert session.active() == hover_target
+    finally:
+        session.mods(0)
+    session.wait_for(r"\[mru\] commit app=%d" % hover_target, timeout=10.0)
+    assert session.active() == hover_target
+
+
+def test_overlay_pointer_click_swallowed(tmp_path):
+    """Clicks while the overlay is up never reach clients: a wltest client
+    with --pointer-out sees buttons with the overlay down and nothing
+    new while Alt is held."""
+    out = tmp_path / "pointer.out"
+    with _run_kick(
+        ["%s --pointer-out '%s' '#ff0000'" % (WL, out)]) as s:
+        s.wait_any_active()
+        s.wait_surface_mapped(0)
+        path = s.dump_host()
+        w, h, _ = s.ppm_rgb(path)
+        s.warp(w // 2, h // 2)
+        s.click()
+        assert _wait_out(out, "button 272 1", timeout=10.0), \
+            f"client saw no click with overlay down: {out.read_text()!r}"
+        n0 = out.read_text().count("button")
+        s.mods(ALT)
+        try:
+            time.sleep(0.7)
+            s.click()
+            time.sleep(0.8)
+        finally:
+            s.mods(0)
+        n1 = out.read_text().count("button")
+        assert n1 == n0, f"click leaked to client while overlay up: {out.read_text()!r}"
+
+
 def test_synth_feed_drives_host_listeners(tmp_path):
     """Synthesized host pointer/touch events go through the real host
     wl_pointer/wl_touch listeners instead of bypassing them for the shared