feat: drag across overlay retargets touch selection

tests/test_smoke.py

@@ -4897,6 +4897,71 @@ def test_overlay_touch_select(session):
     assert session.active() == target
 
 
+def test_overlay_touch_drag(session):
+    """Dragging a finger across the overlay while Alt is held re-targets
+    the preview as the touch slides into each row's titles; sliding out
+    of every row sticks to the last preview; a second finger never steals
+    the drag; lifting commits nothing (Alt release still 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 tapping 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"\[touch\] select app=", session.read_log()))
+            session.touch(7, TOUCH_DOWN, cx, y)
+            time.sleep(0.05)
+            session.touch(7, TOUCH_UP, cx, y)
+            time.sleep(0.12)
+            m = re.findall(r"\[touch\] 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"touch sweep found rows {rows}"
+        yA, yB = sorted(rows.values())
+        # Drag from the upper row into the lower one step by step.
+        base = len(re.findall(r"\[touch\] select app=", session.read_log()))
+        session.touch(7, TOUCH_DOWN, cx, yA)
+        time.sleep(0.2)
+        for yy in range(yA, yB + 1, 10):
+            session.touch(7, TOUCH_MOTION, cx, yy)
+            time.sleep(0.03)
+        time.sleep(0.3)
+        sels = re.findall(r"\[touch\] select app=(\d+)", session.read_log())
+        assert len(sels) > base and sels[base] != sels[-1], \
+            f"drag never re-targeted: {sels[base:]}"
+        drag_target = int(sels[-1])
+        # Sliding out of every row keeps the last preview.
+        n0 = len(re.findall(r"\[touch\] select app=", session.read_log()))
+        session.touch(7, TOUCH_MOTION, 5, 5)
+        time.sleep(0.3)
+        n1 = len(re.findall(r"\[touch\] select app=", session.read_log()))
+        assert n1 == n0, "off-row drag motion changed selection"
+        # A second finger's down+motion never steals the drag.
+        session.touch(9, TOUCH_DOWN, cx, yA)
+        time.sleep(0.1)
+        session.touch(9, TOUCH_MOTION, cx, yB)
+        time.sleep(0.2)
+        n2 = len(re.findall(r"\[touch\] select app=", session.read_log()))
+        session.touch(9, TOUCH_UP, cx, yB)
+        time.sleep(0.1)
+        assert n2 == n1, "second finger stole the overlay drag"
+        session.touch(7, TOUCH_UP, cx, yB)
+        time.sleep(0.2)
+        assert session.active() == drag_target
+    finally:
+        session.mods(0)
+    session.wait_for(r"\[mru\] commit app=%d" % drag_target, timeout=10.0)
+    assert session.active() == drag_target
+
+
 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