[ryoku] shell: read DDC brightness after Controls finishes opening

ryoku/shell/CHANGELOG.md

@@ -1,6 +1,10 @@
 # Changelog: ryoku/shell/
 
 ## Unreleased
+- **Opening Controls no longer makes the whole screen hitch.** With an external
+  monitor on DDC/CI, the panel read its brightness the moment it opened, and that
+  read stalled every display for a fraction of a second. It now reads a quarter
+  second after the panel appears, so the external brightness slider fills in a moment later.
 - **Windows reach the Shima dock again.** Under the Shima bar style the frame and
   the dock both reserved the dock's band, which left a dock-tall gap between
   windows and the dock. The frame's reservation is now the only one there.

ryoku/shell/quickshell/shell/modules/sidebar/ControlsLevels.qml

@@ -45,8 +45,9 @@ Item {
     function syncActive(): void {
         if (root.active && root.showBrightness) {
             Devices.startProbes(root);
-            root.readExternalBrightness();
+            externalReadDelay.restart();
         } else {
+            externalReadDelay.stop();
             root.volumeOpen = false;
             root.brightnessOpen = false;
             root.writeBrightness();
@@ -109,6 +110,15 @@ Item {
         }
     }
 
+    // A DDC/CI read that overlaps the panel's layers mapping stalled every
+    // output's frames for 45-200 ms on each open (seen on NVIDIA I2C); from
+    // 100 ms on there were none, so the live level is read after the map.
+    Timer {
+        id: externalReadDelay
+        interval: 250
+        onTriggered: root.readExternalBrightness()
+    }
+
     Timer {
         id: brightnessWrite
         interval: 90