Make the open-panel mark find and fit its module

A center-anchored module is mounted twice: the copy that is drawn, and a
zero-size placeholder holding its place in the flow beside the anchor.
findPanelWidget returned whichever registered first, and that order is
not stable across a live bar reconfiguration, so a panel could open
anchored to the invisible copy -- mispositioned, with the drawn slot
never lighting up and switchPanelFrom unable to find it again.

The mark was also always 55% of the slot, which fits an icon but
underlines only a fraction of a text label, and runs the full height of a
multi-line module on a vertical bar. Modules can now say how long the
mark should be along the bar; anything that does not answer keeps the old
proportion.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

shell/plugins/bar/Bar.qml

@@ -406,15 +406,19 @@ Item {
   function findPanelWidget(pluginId) {
     var id = String(pluginId || "")
     if (!id) return null
+    var candidates = []
     for (var i = 0; i < moduleSlots.length; i++) {
       var slot = moduleSlots[i]
       if (!slot || !slot.activeItem) continue
       if (slot.moduleName !== id) continue
       var item = slot.activeItem
       if (typeof item.open !== "function" || typeof item.close !== "function" || item.opened === undefined) continue
-      return item
+      candidates.push(slot)
     }
-    return null
+    // Anchored center modules are mounted twice; only the drawn copy can
+    // anchor a popup or carry the open-panel mark. See BarModel.pickDrawnSlot.
+    var chosen = BarModel.pickDrawnSlot(candidates)
+    return chosen ? chosen.activeItem : null
   }
 
   function summonBarWidget(pluginId) {
@@ -1386,6 +1390,16 @@ Item {
     readonly property bool hovered: moduleHover.hovered
     readonly property bool dragSource: root.barDragSource === slot
     readonly property bool panelOpen: root.activePopout === slot.activeItem
+    // Modules bigger than the mark they want (a text label in a padded slot,
+    // a multi-line stack on a vertical bar) can say how long the open-panel
+    // dot should be along the bar, so it tracks what the module paints
+    // instead of a fraction of whatever slot it happens to fill.
+    readonly property real panelIndicatorExtent: {
+      var key = root.vertical ? "openPanelIndicatorHeight" : "openPanelIndicatorWidth"
+      var hint = activeItem && key in activeItem ? activeItem[key] : undefined
+      if (hint !== undefined && hint !== null && hint > 0) return Math.round(hint)
+      return Math.max(Style.space(10), Math.round((root.vertical ? slot.height : slot.width) * 0.55))
+    }
     implicitWidth: activeItem && activeItem.visible ? (root.vertical ? root.barSize : activeItem.implicitWidth) : 0
     implicitHeight: activeItem && activeItem.visible ? activeItem.implicitHeight : 0
     width: implicitWidth
@@ -1455,8 +1469,12 @@ Item {
       opacity: slot.panelOpen && !slot.dragSource ? 0.9 : 0
       color: Color.accent
       radius: Math.min(width, height) / 2
-      width: root.vertical ? Style.space(2) : Math.max(Style.space(10), Math.round(parent.width * 0.55))
-      height: root.vertical ? Math.max(Style.space(10), Math.round(parent.height * 0.55)) : Style.space(2)
+      width: root.vertical ? Style.space(2) : slot.panelIndicatorExtent
+      height: root.vertical ? slot.panelIndicatorExtent : Style.space(2)
+      // The mark sits on the module's inner edge — the one facing the
+      // desktop — so it underlines a top bar, overlines a bottom one, and
+      // points inward from a left or right one. It reads as pointing at the
+      // panel that opens on that side.
       x: root.vertical
         ? (root.position === "left" ? parent.width - width - inset : inset)
         : Math.round((parent.width - width) / 2)

shell/plugins/bar/BarModel.js

@@ -96,8 +96,32 @@ function customModulePath(entry, home, configDir) {
   return source
 }
 
+// A center module is mounted twice once an anchor is set: the copy that is
+// actually drawn, and a zero-size placeholder holding its place in the flow
+// beside the anchor. Panel routing has to pick the drawn one — it is the only
+// one that can anchor a popup, carry the open-panel mark, or be found again
+// by switchPanelFrom — and fall back to the placeholder only when nothing is
+// on screen. The order the two are registered in is not stable across a live
+// bar reconfiguration, so picking the first match is not good enough.
+function isDrawnSlot(slot) {
+  return !!slot && slot.visible === true && slot.width > 0 && slot.height > 0
+}
+
+function pickDrawnSlot(slots) {
+  var placeholder = null
+  var list = slots || []
+  for (var i = 0; i < list.length; i++) {
+    if (!list[i]) continue
+    if (isDrawnSlot(list[i])) return list[i]
+    if (!placeholder) placeholder = list[i]
+  }
+  return placeholder
+}
+
 if (typeof module !== "undefined") {
   module.exports = {
+    isDrawnSlot: isDrawnSlot,
+    pickDrawnSlot: pickDrawnSlot,
     normalizePosition: normalizePosition,
     entrySettings: entrySettings,
     entryId: entryId,