[Bug] Backlight slider stops updating live after control center is closed once

[TimERTy]

Describe the bug
Backlight slider value does not update in real time after the control center has been closed and reopened at least once. First open after swaync start works; every subsequent open, external brightness changes (e.g. brightnessctl, XF86MonBrightnessUp/Down) no longer move the slider while the control center is visible. Volume slider works correctly in the same session.

Root cause
src/controlCenter/widgets/backlight/backlightUtil.vala:

• Constructor creates the FileMonitor exactly once.
• close() (on CC hide) calls monitor.cancel(). GLib FileMonitor is single-use; once cancelled it will not emit further changed signals.
• start() (on CC show) calls connect_monitor() which only re-wires the changed callback onto the already-cancelled monitor. The monitor is never re-created, so no events fire.

To Reproduce

1. Enable backlight widget.
2. Open control center, press XF86MonBrightnessUp — slider updates.
3. Close control center.
4. Open it again, press XF86MonBrightnessUp — slider does not update (brightness itself does change).

Expected behavior
Slider updates every time, as the volume slider does.

Proposed fix
Recreate the FileMonitor in start() before connect_monitor(), or move monitor creation into connect_monitor() itself.

Desktop

• OS: CachyOS (Arch)
• swaync: 0.12.6-1.1
• Compositor: Hyprland
• Device: gmux_backlight (Apple T2 MacBook)

[TimERTy]

Applied the following patch locally against v0.12.6 and the slider now updates live across any number of control-center open/close cycles. Move FileMonitor creation into connect_monitor() (lazy) and null the field in close() so the next start() creates a fresh monitor:

--- a/src/controlCenter/widgets/backlight/backlightUtil.vala
+++ b/src/controlCenter/widgets/backlight/backlightUtil.vala
@@ -66,17 +66,23 @@ namespace SwayNotificationCenter.Widgets {
         }
 
         private void connect_monitor () {
-            if (monitor != null) {
-                // connect monitor to monitor changes
-                monitor.changed.connect ((src, dest, event) => {
-                    get_brightness ();
-                });
+            if (monitor == null) {
+                try {
+                    monitor = fd.monitor (FileMonitorFlags.NONE, null);
+                } catch (Error e) {
+                    critical ("Error %s\n", e.message);
+                    return;
+                }
             }
+            monitor.changed.connect ((src, dest, event) => {
+                get_brightness ();
+            });
         }
 
         public void close () {
             if (monitor != null) {
                 monitor.cancel ();
+                monitor = null;
             }
         }

The initial fd.monitor (...) in the constructor can be dropped as well — the first start() call will create it — but leaving it in place is harmless (replaced on the first close/reopen cycle).

Happy to open a PR if useful.