Long-press popups: one owner, always on screen

- A second long-press finishes the first (typing its choice) before
  opening its own popup, instead of sharing one
- Popups move down over their key when the room above is too small
- No popup over an unknown key: an empty rect made every cell zero wide
- A repeated touch id cancels the stale pointer instead of leaking it

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/tst_keyboardsurface.cpp

@@ -124,6 +124,24 @@ private Q_SLOTS:
         QVERIFY(!surface->alternates()->isOpen());
     }
 
+    void secondLongPressFinishesFirst()
+    {
+        const QPoint e = keyCenter(u"e"_s), u = keyCenter(u"u"_s);
+        auto *surface = qobject_cast<KeyboardSurface *>(keyboard);
+        QTest::touchEvent(&window, touchscreen).press(0, e);
+        QTest::qWait(LongPressWaitMs);
+        QTest::touchEvent(&window, touchscreen).stationary(0).press(1, u);
+        QTest::qWait(LongPressWaitMs); // u's popup replaces e's, which types its choice
+        QCOMPARE(engine.output, u"é");
+        QVERIFY(surface->alternates()->isOpen());
+        QTest::touchEvent(&window, touchscreen).release(0, e).stationary(1);
+        QCOMPARE(engine.output, u"é"); // the first finger's lift does nothing more
+        QVERIFY(surface->alternates()->isOpen());
+        QTest::touchEvent(&window, touchscreen).release(1, u);
+        QCOMPARE(engine.output.size(), 2);
+        QVERIFY(!surface->alternates()->isOpen());
+    }
+
     void secondFingerCommitsFirst()
     {
         const QPoint a = keyCenter(u"a"_s), s = keyCenter(u"s"_s);