Harden display apply and recovery

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

@@ -110,7 +110,7 @@ Column {
                             onTapped: Displays.apply(
                                 root.monitor.name,
                                 rate.modelData.mode,
-                                root.monitor.scale,
+                                Displays.nearestCleanScale(rate.modelData.mode, root.monitor.scale),
                                 root.monitor.transform)
                         }
                     }

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);
     }
 }

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

@@ -28,11 +28,31 @@ Item {
     // scrolls -- the Appearance page pins its live preview here.
     property Component header: null
 
+    Loader {
+        id: pinnedHeader
+
+        anchors.left: parent.left
+        anchors.right: parent.right
+        anchors.top: parent.top
+        anchors.leftMargin: 34
+        anchors.rightMargin: 34
+        anchors.topMargin: 30
+        active: root.header !== null
+        sourceComponent: root.header
+        z: 1
+    }
+
     Flickable {
-        anchors.fill: parent
+        id: pageScroll
+
+        anchors.left: parent.left
+        anchors.right: parent.right
+        anchors.top: pinnedHeader.active ? pinnedHeader.bottom : parent.top
+        anchors.bottom: parent.bottom
+        anchors.topMargin: pinnedHeader.active ? 16 : 0
         clip: true
         contentWidth: width
-        contentHeight: layout.implicitHeight + 64
+        contentHeight: layout.implicitHeight + (pinnedHeader.active ? 34 : 64)
         boundsBehavior: Flickable.StopAtBounds
 
         Column {
@@ -40,15 +60,9 @@ Item {
 
             width: parent.width - 68
             x: 34
-            y: 30
+            y: pinnedHeader.active ? 0 : 30
             spacing: 16
 
-            Loader {
-                width: parent.width
-                active: root.header !== null
-                sourceComponent: root.header
-            }
-
             Text {
                 width: parent.width
                 visible: root.title !== ""