dock: pinned mode acts as screen split - bar shrinks, corners adjust, opaque background

shell/services/DockState.qml

@@ -0,0 +1,38 @@
+pragma Singleton
+
+import QtQuick
+
+QtObject {
+    // "closed" | "pinned" | "overlay"
+    property string mode: "closed"
+    readonly property bool open: mode !== "closed"
+
+    // Screen space reserved by the dock when pinned.
+    // Bar, screen corners, etc. read this to adjust layout.
+    property int reservedWidth: 0
+
+    onModeChanged: {
+        if (mode !== "pinned")
+            reservedWidth = 0;
+    }
+
+    function openPinned() {
+        mode = "pinned";
+    }
+
+    function openOverlay() {
+        if (mode === "closed")
+            mode = "overlay";
+    }
+
+    function close() {
+        mode = "closed";
+    }
+
+    function toggle() {
+        if (mode === "pinned")
+            mode = "closed";
+        else
+            mode = "pinned";
+    }
+}