Cap the menu height at the starting menu's height

The first submenu move or search keystroke already froze the card's top
edge; freeze the rows height at the same moment so drilling into a longer
menu scrolls behind the fold instead of growing the card.

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

shell/plugins/menu/Menu.qml

@@ -152,6 +152,9 @@ Item {
   function availableRowsHeight() {
     var top = panel.cardTop >= 0 ? panel.cardTop : Style.gapsOut
     var available = panel.height - top - Style.gapsOut - root.contentMargin * 2 - root.headerHeight - root.contentSpacing
+    // The starting menu sets the ceiling along with the offset: drilling into
+    // a longer submenu scrolls behind the fold instead of growing the card.
+    if (panel.maxRowsHeight >= 0) available = Math.min(available, panel.maxRowsHeight)
     // A card that swallows the whole screen reads as a page, not a menu.
     return Math.min(available, Math.round(panel.height * 0.6))
   }
@@ -1010,14 +1013,20 @@ Item {
     // The card opens centered exactly as always. The first search keystroke
     // or submenu move freezes the top line where it currently sits — from
     // then on the card grows and shrinks downward instead of re-centering
-    // on every resize, which made the menu jump around. Closing unfreezes.
+    // on every resize, which made the menu jump around. The rows height is
+    // frozen at the same moment, so the starting menu also caps how tall the
+    // card may grow from there. Closing unfreezes both.
     property int cardTop: -1
+    property int maxRowsHeight: -1
     readonly property int centeredTop: Math.max(Style.gapsOut, Math.round((height - root.cardHeight) / 2))
     readonly property int effectiveCardTop: cardTop >= 0 ? cardTop : centeredTop
     function freezeCardTop() {
-      if (visible && cardTop < 0) cardTop = effectiveCardTop
+      if (visible && cardTop < 0) {
+        cardTop = effectiveCardTop
+        maxRowsHeight = root.visibleRowsHeight
+      }
     }
-    onVisibleChanged: if (!visible) cardTop = -1
+    onVisibleChanged: if (!visible) { cardTop = -1; maxRowsHeight = -1 }
 
     Rectangle {
       anchors.fill: parent