Build only the module list the bar is showing

The center section declares both an anchored and an unanchored
arrangement and shows whichever fits, but a hidden ModuleList is still a
loaded Loader. With a center anchor set — the default — every center
module was therefore mounted twice for the life of the session: two IPC
handlers registered for the same target, two clocks ticking, two of every
timer and network fetch behind them, one set of which nothing could
reach.

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

shell/plugins/bar/Bar.qml

@@ -1321,6 +1321,12 @@ Item {
     property string region: ""
 
     visible: entries.length > 0
+    // A hidden list must not build its modules. The center section declares
+    // both an anchored and an unanchored arrangement and shows whichever
+    // fits, so leaving the other one loaded mounts every center module
+    // twice — two IPC handlers registered for the same target, two clocks
+    // ticking, two of every timer and fetch behind them.
+    active: visible && entries.length > 0
     sourceComponent: root.vertical ? verticalModuleList : horizontalModuleList
     width: item ? item.implicitWidth : 0
     height: item ? item.implicitHeight : 0

test/shell.d/bar-test.sh

@@ -19,6 +19,14 @@ const fs = require('fs')
 const bar = requireFromRoot('shell/plugins/bar/BarModel.js')
 const barSource = fs.readFileSync(root + '/shell/plugins/bar/Bar.qml', 'utf8')
 
+// The center section declares two arrangements and shows one; the hidden one
+// must not build its modules or every center widget exists twice.
+const moduleList = barSource.slice(barSource.indexOf('component ModuleList'), barSource.indexOf('component ModuleSlot'))
+assert(
+  /active: visible && entries\.length > 0/.test(moduleList),
+  'bar builds only the module list it is showing'
+)
+
 // A center module is mounted twice — drawn copy plus zero-size placeholder —
 // and the order they register in is not stable across a live reconfiguration,
 // so panel routing has to pick the one that is actually on screen.