Harden display apply and recovery

config/dot/quickshell/modules/settings/DisplaysPage.qml

@@ -21,6 +21,9 @@ SettingsPage {
     lede: SystemSettings.monitorDescription || "Reading the active display…"
 
     readonly property var monitor: Displays.monitors.length > 0 ? Displays.monitors[0] : null
+    readonly property string currentMode: root.monitor
+        ? `${root.monitor.width}x${root.monitor.height}@${Math.round(root.monitor.refreshRate)}`
+        : ""
 
     // The confirmation sits above everything, because while it is counting down
     // it is the only thing that matters on this page.
@@ -76,6 +79,7 @@ SettingsPage {
                     id: keepButton
                     anchors.verticalCenter: parent.verticalCenter
                     text: "Keep"
+                    enabled: Displays.canConfirm
                     onClicked: Displays.confirm()
                 }
             }
@@ -131,7 +135,8 @@ SettingsPage {
             width: parent.width
             label: "Scale"
             detail: "Fractional scales that do not divide the resolution into whole pixels are rejected by the compositor, so only clean ones are offered."
-            options: Displays.scales.map(scale => ({ value: scale, label: scale.toFixed(2) + "×" }))
+            options: Displays.scalesForMode(root.currentMode)
+                .map(scale => ({ value: scale, label: scale.toFixed(2) + "×" }))
             current: root.monitor ? root.monitor.scale : 1
             enabled: !Displays.awaitingConfirmation && !Displays.busy
             onPicked: value => root.applyWith({ scale: value })
@@ -167,11 +172,14 @@ SettingsPage {
     function applyWith(change: var): void {
         if (!root.monitor)
             return;
-        const current = `${root.monitor.width}x${root.monitor.height}@${Math.round(root.monitor.refreshRate)}`;
+        const mode = change.mode ?? root.currentMode;
+        const requestedScale = change.scale ?? root.monitor.scale;
         Displays.apply(
             root.monitor.name,
-            change.mode ?? current,
-            change.scale ?? root.monitor.scale,
+            mode,
+            Displays.isScaleClean(mode, requestedScale)
+                ? requestedScale
+                : Displays.nearestCleanScale(mode, requestedScale),
             change.transform ?? root.monitor.transform);
     }
 }