lightweight variant

CursorLang.Core/AssemblyInfo.cs

@@ -0,0 +1,10 @@
+using System.Runtime.CompilerServices;
+
+// Core keeps its interop and its arithmetic internal, as it always did. The two
+// processes built on it are not outside consumers but the other halves of the same
+// application, so they are let in rather than the surface being widened for them.
+[assembly: InternalsVisibleTo("CursorLang")]
+[assembly: InternalsVisibleTo("CursorLang.Settings")]
+[assembly: InternalsVisibleTo("CursorLang.Core.Tests")]
+[assembly: InternalsVisibleTo("CursorLang.Agent.Tests")]
+[assembly: InternalsVisibleTo("CursorLang.Settings.Tests")]

CursorLang.Core/CursorLang.Core.csproj

@@ -0,0 +1,40 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>net10.0-windows10.0.19041.0</TargetFramework>
+        <SupportedOSPlatformVersion>10.0.17763.0</SupportedOSPlatformVersion>
+        <Nullable>enable</Nullable>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <EnforceCodeStyleInBuild>true</EnforceCodeStyleInBuild>
+        <GenerateDocumentationFile>true</GenerateDocumentationFile>
+        <NoWarn>$(NoWarn);CS1591</NoWarn>
+        <RootNamespace>CursorLang.Core</RootNamespace>
+        <AssemblyName>CursorLang.Core</AssemblyName>
+        <PlatformTarget>AnyCPU</PlatformTarget>
+        <RuntimeIdentifiers>win-x64;win-arm64</RuntimeIdentifiers>
+        <Version>1.0.0</Version>
+        <AssemblyVersion>1.0.0.0</AssemblyVersion>
+        <FileVersion>1.0.0.0</FileVersion>
+        <Product>CursorLang</Product>
+        <Company>Aleksandr Neychev</Company>
+        <Description>Shared part of CursorLang: models, settings, layout tracking, updates</Description>
+        <Copyright>Copyright (c) 2026</Copyright>
+    </PropertyGroup>
+
+    <PropertyGroup>
+        <CaretUiAutomation Condition="'$(CaretUiAutomation)' == ''">true</CaretUiAutomation>
+    </PropertyGroup>
+
+    <PropertyGroup Condition="'$(CaretUiAutomation)' == 'true'">
+        <DefineConstants>$(DefineConstants);CARET_UI_AUTOMATION</DefineConstants>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <FrameworkReference Include="Microsoft.WindowsDesktop.App.WPF" />
+    </ItemGroup>
+
+    <ItemGroup>
+        <PackageReference Include="CommunityToolkit.Mvvm" Version="8.4.2" />
+    </ItemGroup>
+
+</Project>

CursorLang.Core/Interop/CaretNative.cs

@@ -0,0 +1,237 @@
+using System.Runtime.InteropServices;
+#if CARET_UI_AUTOMATION
+using System.Windows.Automation;
+using System.Windows.Automation.Text;
+#endif
+using Accessibility;
+
+namespace CursorLang.Core.Interop;
+
+/// <summary>
+/// Locates the caret in the active input field — including one in another application.
+/// </summary>
+/// <remarks>
+/// There is no single way to do it: classic Win32 applications create a system caret,
+/// while Chrome, Electron and others draw it themselves and report its position only
+/// through accessibility interfaces. So we ask the system first, then the application.
+///
+/// The UI Automation step is behind <c>CARET_UI_AUTOMATION</c>: it is the one part of
+/// the background process that reaches into the WPF half of the desktop runtime —
+/// TextPatternRange hands its rectangles back as System.Windows.Rect, which lives in
+/// WindowsBase — and it was measured at +3.9 MB private. It is also the last of the
+/// three steps and rarely reached. See the switch in CursorLang.Core.csproj.
+/// </remarks>
+internal static class CaretNative
+{
+    [DllImport("user32.dll")]
+    private static extern bool ClientToScreen(IntPtr hWnd, ref PopupWindowNative.Point lpPoint);
+
+    [DllImport("oleacc.dll")]
+    private static extern int AccessibleObjectFromWindow(IntPtr hwnd, uint dwObjectId,
+        ref Guid riid, out IAccessible ppvObject);
+
+    [DllImport("user32.dll")]
+    private static extern bool GetWindowRect(IntPtr hWnd, out PopupWindowNative.Rect lpRect);
+
+    [DllImport("user32.dll")]
+    private static extern uint GetDpiForWindow(IntPtr hWnd);
+
+    private const uint OBJID_CARET = 0xFFFFFFF8;
+    private const int CHILDID_SELF = 0;
+
+    /// <summary>
+    /// The caret rectangle in screen pixels, or <c>null</c> when the active
+    /// application does not report its position.
+    /// </summary>
+    internal static PopupWindowNative.Rect? TryGetCaretRect()
+    {
+        if (!ForegroundInputNative.TryGetInfo(out ForegroundInputNative.GuiThreadInfo info))
+        {
+            return null;
+        }
+
+        PopupWindowNative.Rect? caret = TryGetSystemCaret(info)
+            ?? TryGetAccessibleCaret(info.hwndFocus)
+            ?? TryGetAutomationCaret();
+
+        return caret is null ? null : Validate(caret.Value, info.hwndFocus);
+    }
+
+    /// <summary>
+    /// Filters out obviously wrong coordinates.
+    /// </summary>
+    /// <remarks>
+    /// Some applications report the caret position in their own coordinate system or
+    /// without accounting for display scaling, and the popup ends up far from the input
+    /// field. The caret must be inside the input window — that is what we check, and
+    /// before giving up we try to read the coordinates as unscaled ones.
+    /// </remarks>
+    private static PopupWindowNative.Rect? Validate(PopupWindowNative.Rect caret, IntPtr hwndFocus)
+    {
+        if (hwndFocus == IntPtr.Zero || !GetWindowRect(hwndFocus, out PopupWindowNative.Rect window))
+        {
+            return caret;
+        }
+
+        return Validate(caret, window, GetDpiForWindow(hwndFocus) / 96.0);
+    }
+
+    /// <summary>
+    /// The same check over plain numbers: the input window bounds and the scale of
+    /// its monitor are already known.
+    /// </summary>
+    internal static PopupWindowNative.Rect? Validate(
+        PopupWindowNative.Rect caret, PopupWindowNative.Rect window, double scale)
+    {
+        if (IsInside(caret, window))
+        {
+            return caret;
+        }
+
+        var scaled = new PopupWindowNative.Rect
+        {
+            Left = (int)(caret.Left * scale),
+            Top = (int)(caret.Top * scale),
+            Right = (int)(caret.Right * scale),
+            Bottom = (int)(caret.Bottom * scale),
+        };
+
+        return IsInside(scaled, window) ? scaled : null;
+    }
+
+    internal static bool IsInside(PopupWindowNative.Rect inner, PopupWindowNative.Rect outer) =>
+        inner.Left >= outer.Left && inner.Right <= outer.Right &&
+        inner.Top >= outer.Top && inner.Bottom <= outer.Bottom;
+
+#if CARET_UI_AUTOMATION
+    /// <summary>How long we wait for another application to answer over UI Automation.</summary>
+    private static readonly TimeSpan AutomationTimeout = TimeSpan.FromMilliseconds(150);
+
+    // Browsers and other applications with their own rendering engines draw the caret
+    // themselves and report its position only through UI Automation. The request goes
+    // into another process, so it is the slowest one and comes last
+    private static PopupWindowNative.Rect? TryGetAutomationCaret()
+    {
+        // A hung application must not hang the popup along with it: we wait for the
+        // answer for a limited time, otherwise we show the popup at the cursor
+        Task<PopupWindowNative.Rect?> query = Task.Run(QueryAutomationCaret);
+        return query.Wait(AutomationTimeout) ? query.Result : null;
+    }
+
+    private static PopupWindowNative.Rect? QueryAutomationCaret()
+    {
+        try
+        {
+            AutomationElement focused = AutomationElement.FocusedElement;
+            if (focused is null ||
+                !focused.TryGetCurrentPattern(TextPattern.Pattern, out object pattern))
+            {
+                return null;
+            }
+
+            TextPatternRange[] selection = ((TextPattern)pattern).GetSelection();
+            if (selection.Length == 0)
+            {
+                return null;
+            }
+
+            // The caret has an empty selection and therefore no rectangle,
+            // so we expand it to the nearest character
+            TextPatternRange range = selection[0].Clone();
+            range.ExpandToEnclosingUnit(TextUnit.Character);
+
+            System.Windows.Rect[] rectangles = range.GetBoundingRectangles();
+            if (rectangles.Length == 0 || rectangles[0].Height <= 0)
+            {
+                return null;
+            }
+
+            System.Windows.Rect caret = rectangles[0];
+            return new PopupWindowNative.Rect
+            {
+                Left = (int)caret.Left,
+                Top = (int)caret.Top,
+                Right = (int)caret.Right,
+                Bottom = (int)caret.Bottom,
+            };
+        }
+        catch (Exception e) when (e is ElementNotAvailableException
+                                   or InvalidOperationException
+                                   or COMException)
+        {
+            // The application closed or stopped responding — that must not take the popup down
+            return null;
+        }
+    }
+#else
+    // Built without UI Automation: Chromium and Electron keep the system caret and MSAA
+    // steps above, and where those stay silent the popup falls back to the cursor
+    private static PopupWindowNative.Rect? TryGetAutomationCaret() => null;
+#endif
+
+    // The system caret: its coordinates come relative to the window that owns it
+    private static PopupWindowNative.Rect? TryGetSystemCaret(ForegroundInputNative.GuiThreadInfo info)
+    {
+        if (info.hwndCaret == IntPtr.Zero || IsEmpty(info.rcCaret))
+        {
+            return null;
+        }
+
+        var topLeft = new PopupWindowNative.Point { X = info.rcCaret.Left, Y = info.rcCaret.Top };
+        var bottomRight = new PopupWindowNative.Point { X = info.rcCaret.Right, Y = info.rcCaret.Bottom };
+        if (!ClientToScreen(info.hwndCaret, ref topLeft) || !ClientToScreen(info.hwndCaret, ref bottomRight))
+        {
+            return null;
+        }
+
+        return new PopupWindowNative.Rect
+        {
+            Left = topLeft.X,
+            Top = topLeft.Y,
+            Right = bottomRight.X,
+            Bottom = bottomRight.Y,
+        };
+    }
+
+    // The caret through accessibility interfaces: this is where browsers and Electron land
+    private static PopupWindowNative.Rect? TryGetAccessibleCaret(IntPtr hwndFocus)
+    {
+        if (hwndFocus == IntPtr.Zero)
+        {
+            return null;
+        }
+
+        Guid iid = typeof(IAccessible).GUID;
+        if (AccessibleObjectFromWindow(hwndFocus, OBJID_CARET, ref iid, out IAccessible caret) != 0)
+        {
+            return null;
+        }
+
+        try
+        {
+            caret.accLocation(out int left, out int top, out int width, out int height, CHILDID_SELF);
+            var rect = new PopupWindowNative.Rect
+            {
+                Left = left,
+                Top = top,
+                Right = left + width,
+                Bottom = top + height,
+            };
+
+            return IsEmpty(rect) ? null : rect;
+        }
+        catch (COMException)
+        {
+            // The application declared support but did not report the position
+            return null;
+        }
+        finally
+        {
+            Marshal.ReleaseComObject(caret);
+        }
+    }
+
+    // When there is no caret, its rectangle comes back with zero height.
+    // We judge by height alone: zero coordinates are a normal start of an empty field
+    internal static bool IsEmpty(PopupWindowNative.Rect rect) => rect.Bottom - rect.Top <= 0;
+}

CursorLang.Core/Interop/ForegroundInputNative.cs

@@ -0,0 +1,41 @@
+using System.Runtime.InteropServices;
+
+namespace CursorLang.Core.Interop;
+
+/// <summary>
+/// Input details of the active application: which window holds keyboard focus
+/// and where the caret is.
+/// </summary>
+internal static class ForegroundInputNative
+{
+    [StructLayout(LayoutKind.Sequential)]
+    internal struct GuiThreadInfo
+    {
+        public int cbSize;
+        public uint flags;
+        public IntPtr hwndActive;
+        public IntPtr hwndFocus;
+        public IntPtr hwndCapture;
+        public IntPtr hwndMenuOwner;
+        public IntPtr hwndMoveSize;
+        public IntPtr hwndCaret;
+        public PopupWindowNative.Rect rcCaret;
+    }
+
+    [DllImport("user32.dll")]
+    private static extern bool GetGUIThreadInfo(uint idThread, ref GuiThreadInfo lpgui);
+
+    /// <summary>
+    /// The input state of the foreground thread.
+    /// </summary>
+    /// <remarks>
+    /// The zero thread identifier is not accidental: in modern applications the
+    /// top-level window and the input window live in different threads, and the
+    /// question has to be about the foreground as a whole.
+    /// </remarks>
+    internal static bool TryGetInfo(out GuiThreadInfo info)
+    {
+        info = new GuiThreadInfo { cbSize = Marshal.SizeOf<GuiThreadInfo>() };
+        return GetGUIThreadInfo(0, ref info);
+    }
+}

CursorLang.Core/Interop/ForegroundPermissionNative.cs

@@ -0,0 +1,26 @@
+using System.Runtime.InteropServices;
+
+namespace CursorLang.Core.Interop;
+
+/// <summary>
+/// The right to bring a window to the foreground.
+/// </summary>
+internal static class ForegroundPermissionNative
+{
+    /// <summary>ASFW_ANY — any process gets the right.</summary>
+    private const uint AnyProcess = 0xFFFFFFFF;
+
+    /// <summary>
+    /// Gives up our right to bring a window to the foreground in favour of other processes.
+    /// </summary>
+    /// <remarks>
+    /// Windows does not let just anyone change the foreground window: you have to be
+    /// the process the user interacted with last. An instance started long ago is not
+    /// one of those, and its window will come up only if the right is shared by the
+    /// process the user has just launched.
+    /// </remarks>
+    internal static void GrantToAnyProcess() => AllowSetForegroundWindow(AnyProcess);
+
+    [DllImport("user32.dll")]
+    private static extern bool AllowSetForegroundWindow(uint dwProcessId);
+}

CursorLang.Core/Interop/KeyboardLayoutNative.cs

@@ -0,0 +1,85 @@
+using System.Runtime.InteropServices;
+
+namespace CursorLang.Core.Interop;
+
+/// <summary>
+/// Win32 API for reading the layout of the active application.
+/// </summary>
+internal static class KeyboardLayoutNative
+{
+    private const uint WmInputLangChangeRequest = 0x0050;
+
+    /// <summary>Take the next layout from the system list.</summary>
+    private static readonly IntPtr InputLangChangeForward = new(0x0002);
+
+    /// <summary>HKL_NEXT — the same request in the language of older Windows versions.</summary>
+    private static readonly IntPtr HklNext = new(1);
+
+    [DllImport("user32.dll")]
+    internal static extern IntPtr GetForegroundWindow();
+
+    [DllImport("user32.dll")]
+    private static extern uint GetWindowThreadProcessId(IntPtr hWnd, IntPtr lpdwProcessId);
+
+    [DllImport("user32.dll")]
+    private static extern IntPtr GetKeyboardLayout(uint idThread);
+
+    [DllImport("user32.dll")]
+    private static extern bool PostMessage(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam);
+
+    /// <summary>
+    /// The layout the user is currently typing with.
+    /// </summary>
+    internal static int GetActiveLocaleId() => GetLocaleIdOf(GetInputWindow());
+
+    /// <summary>
+    /// Asks the active application to switch to the next layout from the system list.
+    /// </summary>
+    /// <remarks>
+    /// Synthesizing a system shortcut such as Alt+Shift will not do: the user can
+    /// reassign it in the Windows settings or turn it off entirely. A request sent as
+    /// a message does not depend on those settings and works in another process.
+    /// </remarks>
+    internal static void RequestNextLayout()
+    {
+        IntPtr target = GetInputWindow();
+        if (target == IntPtr.Zero)
+        {
+            return;
+        }
+
+        // Both parameters mean the same thing: different Windows versions and different
+        // UI frameworks look either at the flag or at lParam
+        PostMessage(target, WmInputLangChangeRequest, InputLangChangeForward, HklNext);
+    }
+
+    /// <summary>
+    /// The window that owns keyboard input.
+    /// </summary>
+    /// <remarks>
+    /// We ask the window with keyboard focus rather than the foreground window: in
+    /// Windows 11 Notepad, the Start menu and other WinUI applications the input field
+    /// lives in a separate thread, and the layout changes only for that thread. For the
+    /// main window's thread it stays the same, and the switch goes unnoticed.
+    /// </remarks>
+    private static IntPtr GetInputWindow()
+    {
+        if (ForegroundInputNative.TryGetInfo(out ForegroundInputNative.GuiThreadInfo info) &&
+            info.hwndFocus != IntPtr.Zero)
+        {
+            return info.hwndFocus;
+        }
+
+        return GetForegroundWindow();
+    }
+
+    /// <summary>
+    /// The locale identifier for a window. In Windows the layout is bound to a thread,
+    /// so this reveals it for any application, not only for our own.
+    /// </summary>
+    internal static int GetLocaleIdOf(IntPtr hWnd)
+    {
+        uint threadId = GetWindowThreadProcessId(hWnd, IntPtr.Zero);
+        return (int)GetKeyboardLayout(threadId).ToInt64() & 0xFFFF;
+    }
+}

CursorLang.Core/Interop/LowLevelKeyboardHook.cs

@@ -0,0 +1,130 @@
+using System.Runtime.InteropServices;
+
+namespace CursorLang.Core.Interop;
+
+/// <summary>
+/// A system keyboard hook (WH_KEYBOARD_LL): sees key presses in every application
+/// and can keep them from going any further.
+/// </summary>
+/// <remarks>
+/// Only the low-level hook is installed: a regular WH_KEYBOARD requires injecting a
+/// DLL into other processes, which is impossible for managed code. The callback
+/// arrives on the thread that installed the hook, and that thread must pump a message
+/// loop — hence the requirement to install the hook from the user interface thread.
+/// Returning control must not be delayed: once the system timeout expires, Windows
+/// silently removes the hook.
+/// </remarks>
+internal sealed class LowLevelKeyboardHook : IDisposable
+{
+    /// <summary>
+    /// A key event handler. Returns <c>true</c> when the event must be swallowed —
+    /// then the foreground application will not see it.
+    /// </summary>
+    internal delegate bool KeyFilter(int virtualKey, bool isKeyDown);
+
+    private const int WhKeyboardLowLevel = 13;
+    private const int HcAction = 0;
+
+    private const int WmKeyDown = 0x0100;
+    private const int WmKeyUp = 0x0101;
+    private const int WmSysKeyDown = 0x0104;
+    private const int WmSysKeyUp = 0x0105;
+
+    /// <summary>The event came from SendInput rather than from a real key press.</summary>
+    private const uint LowLevelKeyHookFlagInjected = 0x10;
+
+    private readonly KeyFilter _filter;
+
+    // The delegate lives in a field not for convenience: the only reference to it is
+    // held by Win32, which the garbage collector knows nothing about, and without the
+    // field the hook stops working after a random amount of time
+    private readonly HookProc _callback;
+
+    private IntPtr _handle;
+
+    internal LowLevelKeyboardHook(KeyFilter filter)
+    {
+        _filter = filter;
+        _callback = OnHookEvent;
+    }
+
+    private delegate IntPtr HookProc(int code, IntPtr wParam, IntPtr lParam);
+
+    internal bool IsInstalled => _handle != IntPtr.Zero;
+
+    /// <summary>
+    /// Installs the hook. Returns <c>false</c> when the system refuses.
+    /// </summary>
+    internal bool Install()
+    {
+        if (_handle != IntPtr.Zero)
+        {
+            return true;
+        }
+
+        _handle = SetWindowsHookEx(WhKeyboardLowLevel, _callback, GetModuleHandle(null), 0);
+        return _handle != IntPtr.Zero;
+    }
+
+    internal void Uninstall()
+    {
+        if (_handle == IntPtr.Zero)
+        {
+            return;
+        }
+
+        UnhookWindowsHookEx(_handle);
+        _handle = IntPtr.Zero;
+    }
+
+    public void Dispose() => Uninstall();
+
+    [DllImport("user32.dll", SetLastError = true)]
+    private static extern IntPtr SetWindowsHookEx(int idHook, HookProc lpfn, IntPtr hMod, uint dwThreadId);
+
+    [DllImport("user32.dll", SetLastError = true)]
+    private static extern bool UnhookWindowsHookEx(IntPtr hhk);
+
+    [DllImport("user32.dll")]
+    private static extern IntPtr CallNextHookEx(IntPtr hhk, int code, IntPtr wParam, IntPtr lParam);
+
+    [DllImport("kernel32.dll", CharSet = CharSet.Unicode)]
+    private static extern IntPtr GetModuleHandle(string? lpModuleName);
+
+    private IntPtr OnHookEvent(int code, IntPtr wParam, IntPtr lParam)
+    {
+        if (code != HcAction)
+        {
+            return CallNextHookEx(_handle, code, wParam, lParam);
+        }
+
+        var message = (int)wParam;
+        bool isKeyDown = message is WmKeyDown or WmSysKeyDown;
+        bool isKeyUp = message is WmKeyUp or WmSysKeyUp;
+
+        var data = Marshal.PtrToStructure<KeyboardHookData>(lParam);
+
+        // Synthetic input comes from on-screen keyboards, text expanders and
+        // automation tools: overriding what they do is none of our business
+        bool injected = (data.flags & LowLevelKeyHookFlagInjected) != 0;
+
+        if ((isKeyDown || isKeyUp) && !injected && _filter((int)data.vkCode, isKeyDown))
+        {
+            // A non-zero result instead of CallNextHookEx breaks the chain: the event
+            // will reach neither the application nor the Windows caps-lock handler
+            return 1;
+        }
+
+        return CallNextHookEx(_handle, code, wParam, lParam);
+    }
+
+    [StructLayout(LayoutKind.Sequential)]
+    private struct KeyboardHookData
+    {
+        public uint vkCode;
+        public uint scanCode;
+        public uint flags;
+        public uint time;
+        public IntPtr dwExtraInfo;
+    }
+}

CursorLang.Core/Interop/PackageIdentityNative.cs

@@ -0,0 +1,38 @@
+using System.Runtime.InteropServices;
+
+namespace CursorLang.Core.Interop;
+
+/// <summary>
+/// Answers whether the application runs from an MSIX package.
+/// </summary>
+/// <remarks>
+/// The same application runs both installed from the Store and simply unpacked
+/// into a folder. Some Windows features — startup through <c>StartupTask</c>, for
+/// instance — are available only to a package, and reaching for them without a
+/// check is not allowed: outside a package they throw.
+/// </remarks>
+internal static class PackageIdentityNative
+{
+    /// <summary>APPMODEL_ERROR_NO_PACKAGE — the process runs outside a package.</summary>
+    private const int NoPackage = 15700;
+
+    /// <summary>
+    /// The application runs from an MSIX package.
+    /// </summary>
+    /// <remarks>
+    /// The value is computed once: it cannot change during the lifetime of
+    /// the process.
+    /// </remarks>
+    internal static bool IsPackaged { get; } = DetectPackage();
+
+    private static bool DetectPackage()
+    {
+        // The answer comes from the return code rather than from the name itself, so
+        // no buffer is needed: with zero length a package replies complaining about space
+        uint length = 0;
+        return GetCurrentPackageFullName(ref length, IntPtr.Zero) != NoPackage;
+    }
+
+    [DllImport("kernel32.dll", CharSet = CharSet.Unicode)]
+    private static extern int GetCurrentPackageFullName(ref uint packageFullNameLength, IntPtr packageFullName);
+}

CursorLang.Core/Interop/PopupWindowNative.cs

@@ -0,0 +1,149 @@
+using System.Runtime.InteropServices;
+
+namespace CursorLang.Core.Interop;
+
+/// <summary>
+/// Win32 API for the popup window: styles, positioning near the cursor
+/// and the scale of the monitor the cursor is on.
+/// </summary>
+internal static class PopupWindowNative
+{
+    [StructLayout(LayoutKind.Sequential)]
+    internal struct Point
+    {
+        public int X;
+        public int Y;
+    }
+
+    [DllImport("user32.dll")]
+    private static extern bool GetCursorPos(out Point lpPoint);
+
+    [DllImport("user32.dll")]
+    private static extern IntPtr GetForegroundWindow();
+
+    [DllImport("user32.dll", SetLastError = true)]
+    private static extern int GetWindowLong(IntPtr hWnd, int nIndex);
+
+    [DllImport("user32.dll")]
+    private static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);
+
+    [DllImport("user32.dll")]
+    private static extern bool SetWindowPos(IntPtr hWnd, IntPtr hWndInsertAfter,
+        int X, int Y, int cx, int cy, uint uFlags);
+
+    [DllImport("user32.dll")]
+    private static extern IntPtr MonitorFromPoint(Point pt, uint dwFlags);
+
+    [DllImport("shcore.dll")]
+    private static extern int GetDpiForMonitor(IntPtr hMonitor, int dpiType, out uint dpiX, out uint dpiY);
+
+    [DllImport("user32.dll")]
+    private static extern IntPtr MonitorFromWindow(IntPtr hWnd, uint dwFlags);
+
+    [DllImport("user32.dll")]
+    private static extern bool GetMonitorInfo(IntPtr hMonitor, ref MonitorInfo lpmi);
+
+    [StructLayout(LayoutKind.Sequential)]
+    internal struct Rect
+    {
+        public int Left;
+        public int Top;
+        public int Right;
+        public int Bottom;
+    }
+
+    [StructLayout(LayoutKind.Sequential)]
+    private struct MonitorInfo
+    {
+        public int cbSize;
+        public Rect rcMonitor;
+        public Rect rcWork;
+        public uint dwFlags;
+    }
+
+    private const int GWL_EXSTYLE = -20;
+    // The window does not take focus away from the active application
+    private const int WS_EX_NOACTIVATE = 0x08000000;
+    // And does not show up in Alt+Tab
+    private const int WS_EX_TOOLWINDOW = 0x00000080;
+
+    private const uint SWP_NOSIZE = 0x0001;
+    private const uint SWP_NOZORDER = 0x0004;
+    private const uint SWP_NOACTIVATE = 0x0010;
+
+    private const uint MONITOR_DEFAULTTONEAREST = 2;
+    private const int MDT_EFFECTIVE_DPI = 0;
+
+    internal static Point GetCursorPosition()
+    {
+        GetCursorPos(out Point cursor);
+        return cursor;
+    }
+
+    /// <summary>
+    /// The popup shows up on top of other applications, so it must neither
+    /// activate itself nor steal input focus from the active window.
+    /// </summary>
+    internal static void MakePassive(IntPtr hWnd)
+    {
+        int exStyle = GetWindowLong(hWnd, GWL_EXSTYLE);
+        SetWindowLong(hWnd, GWL_EXSTYLE, exStyle | WS_EX_NOACTIVATE | WS_EX_TOOLWINDOW);
+    }
+
+    /// <summary>
+    /// Moves the window to a screen point without changing its size or z-order.
+    /// The coordinates are physical pixels: monitors have different scaling, while
+    /// Window.Left/Top are converted using the DPI of the monitor the window is on
+    /// right now, which misses the target on a neighbouring monitor.
+    /// </summary>
+    internal static void MoveTo(IntPtr hWnd, int x, int y)
+    {
+        SetWindowPos(hWnd, IntPtr.Zero, x, y, 0, 0, SWP_NOSIZE | SWP_NOZORDER | SWP_NOACTIVATE);
+    }
+
+    /// <summary>
+    /// Sets the window position and size in physical pixels.
+    /// </summary>
+    /// <remarks>
+    /// The size is set this way rather than through Width/Height: on the first show the
+    /// window is still subject to the system minimum window size (SM_CXMIN×SM_CYMIN)
+    /// and the popup comes out noticeably larger than its text. By the time this is
+    /// called the window is already shown and has become a popup window, which that
+    /// restriction does not apply to.
+    /// </remarks>
+    internal static void SetBounds(IntPtr hWnd, int x, int y, int width, int height)
+    {
+        SetWindowPos(hWnd, IntPtr.Zero, x, y, width, height, SWP_NOZORDER | SWP_NOACTIVATE);
+    }
+
+    /// <summary>The scale of the monitor the point is on (1.0 at 96 DPI).</summary>
+    internal static double GetScaleAt(Point point) =>
+        GetScaleOf(MonitorFromPoint(point, MONITOR_DEFAULTTONEAREST));
+
+    /// <summary>
+    /// The work area of the monitor holding the active window — without the taskbar —
+    /// and its scale. That is the monitor the user is working on right now.
+    /// </summary>
+    internal static (Rect WorkArea, double Scale) GetActiveMonitorWorkArea()
+    {
+        IntPtr monitor = MonitorFromWindow(GetForegroundWindow(), MONITOR_DEFAULTTONEAREST);
+
+        var info = new MonitorInfo { cbSize = Marshal.SizeOf<MonitorInfo>() };
+        if (!GetMonitorInfo(monitor, ref info))
+        {
+            return (new Rect(), 1.0);
+        }
+
+        return (info.rcWork, GetScaleOf(monitor));
+    }
+
+    private static double GetScaleOf(IntPtr monitor)
+    {
+        if (GetDpiForMonitor(monitor, MDT_EFFECTIVE_DPI, out uint dpiX, out _) < 0)
+        {
+            return 1.0;
+        }
+
+        return dpiX / 96.0;
+    }
+}

CursorLang.Core/Models/AppSettings.cs

@@ -0,0 +1,150 @@
+using System.Drawing;
+using System.Text.Json.Serialization;
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace CursorLang.Core.Models;
+
+/// <summary>
+/// The application settings, as the settings window writes them to settings.json.
+/// </summary>
+/// <remarks>
+/// The colours are <see cref="System.Drawing.Color"/> rather than
+/// <c>System.Windows.Media.Color</c>. The former lives in System.Drawing.Primitives,
+/// which is part of the base runtime and brings neither WPF nor GDI+ along; the latter
+/// is WindowsBase, and this type is read by the agent, which must stay clear of it.
+/// The settings window turns them into brushes in its converters.
+///
+/// Both processes hold an instance of this, but only the settings window writes: the
+/// agent re-reads the file and pours the fresh values into the instance it already has,
+/// so everything subscribed to it stays subscribed. See <see cref="CopyFrom"/>.
+/// </remarks>
+public sealed partial class AppSettings : ObservableObject
+{
+    /// <summary>The interface language as a culture code: "ru", "en".</summary>
+    [ObservableProperty]
+    private string _language = "en";
+
+    /// <summary>The look of the settings window.</summary>
+    [ObservableProperty]
+    private AppTheme _theme = AppTheme.System;
+
+    /// <summary>Where the popup is shown: at the cursor, at the caret or at a fixed point.</summary>
+    [ObservableProperty]
+    private PopupPlacementMode _placementMode = PopupPlacementMode.AtCursor;
+
+    // The side and the offset are stored per mode: the cursor and the caret call for
+    // different settings, and switching the mode does not reset them
+
+    /// <summary>The side of the cursor the popup is put on.</summary>
+    [ObservableProperty]
+    private AnchorSide _cursorSide = AnchorSide.BottomRight;
+
+    /// <summary>The offset from the cursor in WPF units.</summary>
+    [ObservableProperty]
+    private double _cursorOffset = 16;
+
+    /// <summary>The side of the caret the popup is put on.</summary>
+    [ObservableProperty]
+    private AnchorSide _caretSide = AnchorSide.BottomRight;
+
+    /// <summary>The offset from the caret in WPF units.</summary>
+    [ObservableProperty]
+    private double _caretOffset = 16;
+
+    /// <summary>
+    /// The place on the monitor for the <see cref="PopupPlacementMode.FixedPoint"/> mode.
+    /// </summary>
+    [ObservableProperty]
+    private ScreenPosition _screenPosition = ScreenPosition.BottomRight;
+
+    /// <summary>The offset from the monitor edge in WPF units.</summary>
+    [ObservableProperty]
+    private double _screenMargin = 24;
+
+    /// <summary>The size of the layout name in the popup, in WPF units.</summary>
+    [ObservableProperty]
+    private double _fontSize = 20;
+
+    /// <summary>The popup opacity: 1.0 is fully opaque.</summary>
+    [ObservableProperty]
+    private double _opacity = 0.9;
+
+    /// <summary>How long the popup stays on screen, in milliseconds.</summary>
+    [ObservableProperty]
+    private double _durationMilliseconds = 500;
+
+    /// <summary>
+    /// Intercept Caps Lock and switch the layout with it instead of changing the case.
+    /// Off by default: the application must not change the behaviour of the system
+    /// until it is asked to.
+    /// </summary>
+    [ObservableProperty]
+    private bool _useCapsLockHotkey;
+
+    /// <summary>
+    /// After how long a Caps Lock hold cancels the switch, in milliseconds.
+    /// </summary>
+    [ObservableProperty]
+    private double _capsLockHoldMilliseconds = 300;
+
+    /// <summary>
+    /// Ask the repository about new versions on startup. A check can always be
+    /// started by hand — this setting turns off only the automatic one.
+    /// </summary>
+    [ObservableProperty]
+    private bool _checkForUpdates = true;
+
+    /// <summary>
+    /// When the application last asked about new versions successfully.
+    /// Stored so as not to go to the network on every startup.
+    /// </summary>
+    [ObservableProperty]
+    private DateTimeOffset? _lastUpdateCheck;
+
+    /// <summary>The fill of the popup. The opacity is set by <see cref="Opacity"/>.</summary>
+    [ObservableProperty]
+    private Color _backgroundColor = Color.FromArgb(0xFF, 0x20, 0x20, 0x20);
+
+    /// <summary>The colour of the layout name in the popup.</summary>
+    [ObservableProperty]
+    private Color _foregroundColor = Color.FromArgb(0xFF, 0xFF, 0xFF, 0xFF);
+
+    /// <summary><see cref="DurationMilliseconds"/> as a <see cref="TimeSpan"/>.</summary>
+    [JsonIgnore]
+    public TimeSpan Duration => TimeSpan.FromMilliseconds(DurationMilliseconds);
+
+    /// <summary><see cref="CapsLockHoldMilliseconds"/> as a <see cref="TimeSpan"/>.</summary>
+    [JsonIgnore]
+    public TimeSpan CapsLockHoldDelay => TimeSpan.FromMilliseconds(CapsLockHoldMilliseconds);
+
+    /// <summary>
+    /// Takes the values of another instance over, raising a change notification for
+    /// every property that has actually moved.
+    /// </summary>
+    /// <remarks>
+    /// This is how the agent learns about an edit: the settings window is a separate
+    /// process, so the fresh values arrive as a freshly parsed instance and are poured
+    /// into the one everything is already bound to, rather than replacing it.
+    /// </remarks>
+    public void CopyFrom(AppSettings other)
+    {
+        Language = other.Language;
+        Theme = other.Theme;
+        PlacementMode = other.PlacementMode;
+        CursorSide = other.CursorSide;
+        CursorOffset = other.CursorOffset;
+        CaretSide = other.CaretSide;
+        CaretOffset = other.CaretOffset;
+        ScreenPosition = other.ScreenPosition;
+        ScreenMargin = other.ScreenMargin;
+        FontSize = other.FontSize;
+        Opacity = other.Opacity;
+        DurationMilliseconds = other.DurationMilliseconds;
+        UseCapsLockHotkey = other.UseCapsLockHotkey;
+        CapsLockHoldMilliseconds = other.CapsLockHoldMilliseconds;
+        CheckForUpdates = other.CheckForUpdates;
+        LastUpdateCheck = other.LastUpdateCheck;
+        BackgroundColor = other.BackgroundColor;
+        ForegroundColor = other.ForegroundColor;
+    }
+}

CursorLang.Core/Models/AppTheme.cs

@@ -0,0 +1,12 @@
+namespace CursorLang.Core.Models;
+
+/// <summary>
+/// The look of the settings window. By default the application follows the Windows
+/// theme, but the user can pin the light or the dark one.
+/// </summary>
+public enum AppTheme
+{
+    System,
+    Light,
+    Dark
+}

CursorLang.Core/Models/KeyboardLayout.cs

@@ -0,0 +1,41 @@
+using System.Globalization;
+
+namespace CursorLang.Core.Models;
+
+/// <summary>
+/// A keyboard layout in a form convenient for display.
+/// </summary>
+/// <param name="LocaleId">The locale identifier (the low word of HKL).</param>
+/// <param name="ShortName">A short name for the popup at the cursor, "RU" for instance.</param>
+/// <param name="DisplayName">The full name, "RU — русский (Россия)" for instance.</param>
+public sealed record KeyboardLayout(int LocaleId, string ShortName, string DisplayName)
+{
+    /// <summary>
+    /// Builds the model from a locale identifier. Unknown locales are not an
+    /// error: for them we show the identifier itself.
+    /// </summary>
+    public static KeyboardLayout FromLocaleId(int localeId)
+    {
+        CultureInfo? culture = TryGetCulture(localeId);
+        if (culture is null)
+        {
+            string fallback = $"0x{localeId:X4}";
+            return new KeyboardLayout(localeId, fallback, fallback);
+        }
+
+        string shortName = culture.TwoLetterISOLanguageName.ToUpperInvariant();
+        return new KeyboardLayout(localeId, shortName, $"{shortName} — {culture.NativeName}");
+    }
+
+    private static CultureInfo? TryGetCulture(int localeId)
+    {
+        try
+        {
+            return new CultureInfo(localeId);
+        }
+        catch (CultureNotFoundException)
+        {
+            return null;
+        }
+    }
+}

CursorLang.Core/Models/LayoutChangedEventArgs.cs

@@ -0,0 +1,23 @@
+namespace CursorLang.Core.Models;
+
+/// <summary>
+/// Why the current layout has changed.
+/// </summary>
+public enum LayoutChangeReason
+{
+    /// <summary>The user switched the layout in the active application.</summary>
+    UserSwitched,
+
+    /// <summary>The user moved to another application that has a layout of its own.</summary>
+    ApplicationSwitched,
+}
+
+/// <summary>
+/// The data of a layout change event.
+/// </summary>
+public sealed class LayoutChangedEventArgs(KeyboardLayout layout, LayoutChangeReason reason) : EventArgs
+{
+    public KeyboardLayout Layout { get; } = layout;
+
+    public LayoutChangeReason Reason { get; } = reason;
+}

CursorLang.Core/Models/PopupPlacement.cs

@@ -0,0 +1,46 @@
+namespace CursorLang.Core.Models;
+
+/// <summary>
+/// How the place for the popup is chosen.
+/// </summary>
+public enum PopupPlacementMode
+{
+    /// <summary>Next to the mouse cursor.</summary>
+    AtCursor,
+
+    /// <summary>
+    /// Next to the caret in the active input field. When the application does not
+    /// report its position, the popup is shown at the mouse cursor.
+    /// </summary>
+    AtCaret,
+
+    /// <summary>At a fixed point of the monitor holding the active window.</summary>
+    FixedPoint,
+}
+
+/// <summary>
+/// Which side of the cursor or the caret to show the popup on.
+/// </summary>
+public enum AnchorSide
+{
+    TopLeft,
+    TopRight,
+    Left,
+    Right,
+    BottomLeft,
+    BottomRight,
+}
+
+/// <summary>
+/// The place on the monitor for the <see cref="PopupPlacementMode.FixedPoint"/> mode.
+/// </summary>
+public enum ScreenPosition
+{
+    TopLeft,
+    Top,
+    TopRight,
+    Center,
+    BottomLeft,
+    Bottom,
+    BottomRight,
+}

CursorLang.Core/Models/ReleaseInfo.cs

@@ -0,0 +1,18 @@
+namespace CursorLang.Core.Models;
+
+/// <summary>
+/// A file attached to a release.
+/// </summary>
+/// <param name="FileName">The name the file is saved to disk under.</param>
+/// <param name="Url">A direct link to the content.</param>
+/// <param name="Size">The size in bytes; zero when the hosting did not report it.</param>
+public sealed record ReleaseAsset(string FileName, Uri Url, long Size);
+
+/// <summary>
+/// A release found in the repository.
+/// </summary>
+/// <param name="Version">The version parsed from the tag.</param>
+/// <param name="Tag">The tag as is — that is what the interface shows.</param>
+/// <param name="PageUrl">The release page: the release notes live there too.</param>
+/// <param name="Package">The MSIX package the application updates itself with.</param>
+public sealed record ReleaseInfo(Version Version, string Tag, Uri? PageUrl, ReleaseAsset Package);

CursorLang.Core/Models/StartupState.cs

@@ -0,0 +1,30 @@
+namespace CursorLang.Core.Models;
+
+/// <summary>
+/// The state of startup. Follows <c>StartupTaskState</c> of Windows: the user and
+/// the administrator each have their own way of forbidding startup, and the app has
+/// to tell them apart so as not to promise what it cannot do.
+/// </summary>
+public enum StartupState
+{
+    /// <summary>Windows will not answer about startup — the setting is not shown.</summary>
+    Unavailable,
+
+    /// <summary>Off, and the app can switch it on.</summary>
+    Disabled,
+
+    /// <summary>On.</summary>
+    Enabled,
+
+    /// <summary>
+    /// Switched off by the user in the settings of Windows. It goes back on only
+    /// there: a ban by the user is not for the app to overrule.
+    /// </summary>
+    DisabledByUser,
+
+    /// <summary>Forbidden by the policy of the organisation.</summary>
+    DisabledByPolicy,
+
+    /// <summary>Switched on by the policy of the organisation and not to be switched off.</summary>
+    EnabledByPolicy,
+}

CursorLang.Core/Models/UpdateStatus.cs

@@ -0,0 +1,29 @@
+namespace CursorLang.Core.Models;
+
+/// <summary>
+/// Which step the update is at. One value — one state of the interface:
+/// the caption, the button and the progress bar are shown from it.
+/// </summary>
+public enum UpdateStatus
+{
+    /// <summary>There have been no checks yet.</summary>
+    Idle,
+
+    /// <summary>A request to the repository is in flight.</summary>
+    Checking,
+
+    /// <summary>The latest version is installed.</summary>
+    UpToDate,
+
+    /// <summary>There is a newer version — it can be downloaded.</summary>
+    Available,
+
+    /// <summary>The package is downloading.</summary>
+    Downloading,
+
+    /// <summary>The package is downloaded and ready to install.</summary>
+    Ready,
+
+    /// <summary>The check or the download failed.</summary>
+    Failed,
+}

CursorLang.Core/Resources/Strings.resx

@@ -0,0 +1,250 @@
+<?xml version="1.0" encoding="utf-8"?>
+<root>
+  <xsd:schema id="root" xmlns="" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
+    <xsd:import namespace="http://www.w3.org/XML/1998/namespace" />
+    <xsd:element name="root" msdata:IsDataSet="true">
+      <xsd:complexType>
+        <xsd:choice maxOccurs="unbounded">
+          <xsd:element name="metadata">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" />
+              </xsd:sequence>
+              <xsd:attribute name="name" use="required" type="xsd:string" />
+              <xsd:attribute name="type" type="xsd:string" />
+              <xsd:attribute name="mimetype" type="xsd:string" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="assembly">
+            <xsd:complexType>
+              <xsd:attribute name="alias" type="xsd:string" />
+              <xsd:attribute name="name" type="xsd:string" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="data">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+                <xsd:element name="comment" type="xsd:string" minOccurs="0" msdata:Ordinal="2" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" msdata:Ordinal="1" />
+              <xsd:attribute name="type" type="xsd:string" msdata:Ordinal="3" />
+              <xsd:attribute name="mimetype" type="xsd:string" msdata:Ordinal="4" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="resheader">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" />
+            </xsd:complexType>
+          </xsd:element>
+        </xsd:choice>
+      </xsd:complexType>
+    </xsd:element>
+  </xsd:schema>
+  <resheader name="resmimetype">
+    <value>text/microsoft-resx</value>
+  </resheader>
+  <resheader name="version">
+    <value>2.0</value>
+  </resheader>
+  <resheader name="reader">
+    <value>System.Resources.ResXResourceReader, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+  <resheader name="writer">
+    <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+  <data name="SettingsTitle" xml:space="preserve">
+    <value>CursorLang — Settings</value>
+  </data>
+  <data name="TrayMenuSettings" xml:space="preserve">
+    <value>Settings</value>
+  </data>
+  <data name="TrayMenuExit" xml:space="preserve">
+    <value>Exit</value>
+  </data>
+  <data name="SectionInterface" xml:space="preserve">
+    <value>Interface</value>
+  </data>
+  <data name="LanguageLabel" xml:space="preserve">
+    <value>Interface language</value>
+  </data>
+  <data name="ThemeLabel" xml:space="preserve">
+    <value>Theme</value>
+  </data>
+  <data name="AppTheme_System" xml:space="preserve">
+    <value>Same as Windows</value>
+  </data>
+  <data name="AppTheme_Light" xml:space="preserve">
+    <value>Light</value>
+  </data>
+  <data name="AppTheme_Dark" xml:space="preserve">
+    <value>Dark</value>
+  </data>
+  <data name="SectionPlacement" xml:space="preserve">
+    <value>Placement</value>
+  </data>
+  <data name="PlacementModeLabel" xml:space="preserve">
+    <value>Mode</value>
+  </data>
+  <data name="PopupPlacementMode_AtCursor" xml:space="preserve">
+    <value>Near the cursor</value>
+  </data>
+  <data name="PopupPlacementMode_AtCaret" xml:space="preserve">
+    <value>Near the text caret</value>
+  </data>
+  <data name="PopupPlacementMode_FixedPoint" xml:space="preserve">
+    <value>Fixed point on screen</value>
+  </data>
+  <data name="CursorCornerLabel" xml:space="preserve">
+    <value>Side</value>
+  </data>
+  <data name="AnchorSide_BottomRight" xml:space="preserve">
+    <value>Bottom right</value>
+  </data>
+  <data name="AnchorSide_BottomLeft" xml:space="preserve">
+    <value>Bottom left</value>
+  </data>
+  <data name="AnchorSide_TopRight" xml:space="preserve">
+    <value>Top right</value>
+  </data>
+  <data name="AnchorSide_TopLeft" xml:space="preserve">
+    <value>Top left</value>
+  </data>
+  <data name="AnchorSide_Left" xml:space="preserve">
+    <value>Left</value>
+  </data>
+  <data name="AnchorSide_Right" xml:space="preserve">
+    <value>Right</value>
+  </data>
+  <data name="CursorOffsetLabel" xml:space="preserve">
+    <value>Offset</value>
+  </data>
+  <data name="ScreenPositionLabel" xml:space="preserve">
+    <value>Position on screen</value>
+  </data>
+  <data name="ScreenPosition_TopLeft" xml:space="preserve">
+    <value>Top left</value>
+  </data>
+  <data name="ScreenPosition_Top" xml:space="preserve">
+    <value>Top center</value>
+  </data>
+  <data name="ScreenPosition_Bottom" xml:space="preserve">
+    <value>Bottom center</value>
+  </data>
+  <data name="ScreenPosition_TopRight" xml:space="preserve">
+    <value>Top right</value>
+  </data>
+  <data name="ScreenPosition_BottomLeft" xml:space="preserve">
+    <value>Bottom left</value>
+  </data>
+  <data name="ScreenPosition_BottomRight" xml:space="preserve">
+    <value>Bottom right</value>
+  </data>
+  <data name="ScreenPosition_Center" xml:space="preserve">
+    <value>Center</value>
+  </data>
+  <data name="ScreenMarginLabel" xml:space="preserve">
+    <value>Margin from screen edge</value>
+  </data>
+  <data name="SectionAppearance" xml:space="preserve">
+    <value>Appearance</value>
+  </data>
+  <data name="FontSizeLabel" xml:space="preserve">
+    <value>Font size</value>
+  </data>
+  <data name="OpacityLabel" xml:space="preserve">
+    <value>Opacity</value>
+  </data>
+  <data name="BackgroundColorLabel" xml:space="preserve">
+    <value>Background color</value>
+  </data>
+  <data name="TextColorLabel" xml:space="preserve">
+    <value>Text color</value>
+  </data>
+  <data name="SectionBehavior" xml:space="preserve">
+    <value>Behavior</value>
+  </data>
+  <data name="DurationLabel" xml:space="preserve">
+    <value>Display time</value>
+  </data>
+  <data name="PreviewLabel" xml:space="preserve">
+    <value>Preview</value>
+  </data>
+  <data name="MillisecondsSuffix" xml:space="preserve">
+    <value>ms</value>
+  </data>
+  <data name="CapsLockLabel" xml:space="preserve">
+    <value>Caps Lock</value>
+  </data>
+  <data name="CapsLockHotkeyCheck" xml:space="preserve">
+    <value>Switch the layout instead of changing case</value>
+  </data>
+  <data name="CapsLockHoldLabel" xml:space="preserve">
+    <value>Hold threshold</value>
+  </data>
+  <data name="CapsLockHoldHint" xml:space="preserve">
+    <value>Holding the key longer shows the tooltip without switching the layout.</value>
+  </data>
+  <data name="MoreInfoLink" xml:space="preserve">
+    <value>More info</value>
+  </data>
+  <data name="CapsLockElevationHint" xml:space="preserve">
+    <value>The shortcut has no effect while a window running as administrator is in focus — Task Manager, Registry Editor, UAC prompts. Windows does not deliver keystrokes there to ordinary applications. The tooltip itself keeps working everywhere.</value>
+  </data>
+  <data name="StartupLabel" xml:space="preserve">
+    <value>Startup</value>
+  </data>
+  <data name="StartupCheck" xml:space="preserve">
+    <value>Start with Windows</value>
+  </data>
+  <data name="StartupLockedHint" xml:space="preserve">
+    <value>Startup for this app is now controlled by Windows: Settings — Apps — Startup.</value>
+  </data>
+  <data name="SectionUpdates" xml:space="preserve">
+    <value>Updates</value>
+  </data>
+  <data name="CurrentVersionLabel" xml:space="preserve">
+    <value>Installed version</value>
+  </data>
+  <data name="CheckUpdatesButton" xml:space="preserve">
+    <value>Check for updates</value>
+  </data>
+  <data name="UpdateAutoCheck" xml:space="preserve">
+    <value>Check for updates</value>
+  </data>
+  <data name="UpdateChecking" xml:space="preserve">
+    <value>Checking for updates…</value>
+  </data>
+  <data name="UpdateUpToDate" xml:space="preserve">
+    <value>The installed version is the latest one.</value>
+  </data>
+  <data name="UpdateAvailable" xml:space="preserve">
+    <value>Version {0} is available.</value>
+  </data>
+  <data name="UpdateDownloading" xml:space="preserve">
+    <value>Downloading the package…</value>
+  </data>
+  <data name="UpdateReady" xml:space="preserve">
+    <value>The package has been downloaded.</value>
+  </data>
+  <data name="UpdateFailed" xml:space="preserve">
+    <value>Could not reach the releases. Check the connection and try again.</value>
+  </data>
+  <data name="DownloadUpdateButton" xml:space="preserve">
+    <value>Download</value>
+  </data>
+  <data name="InstallUpdateButton" xml:space="preserve">
+    <value>Install</value>
+  </data>
+  <data name="ReleasePageLink" xml:space="preserve">
+    <value>Release page</value>
+  </data>
+  <data name="UpdateInstallHint" xml:space="preserve">
+    <value>Windows will show the package and ask to confirm the installation. The new version takes over once the app is restarted.</value>
+  </data>
+</root>

CursorLang.Core/Resources/Strings.ru.resx

@@ -0,0 +1,250 @@
+<?xml version="1.0" encoding="utf-8"?>
+<root>
+  <xsd:schema id="root" xmlns="" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
+    <xsd:import namespace="http://www.w3.org/XML/1998/namespace" />
+    <xsd:element name="root" msdata:IsDataSet="true">
+      <xsd:complexType>
+        <xsd:choice maxOccurs="unbounded">
+          <xsd:element name="metadata">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" />
+              </xsd:sequence>
+              <xsd:attribute name="name" use="required" type="xsd:string" />
+              <xsd:attribute name="type" type="xsd:string" />
+              <xsd:attribute name="mimetype" type="xsd:string" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="assembly">
+            <xsd:complexType>
+              <xsd:attribute name="alias" type="xsd:string" />
+              <xsd:attribute name="name" type="xsd:string" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="data">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+                <xsd:element name="comment" type="xsd:string" minOccurs="0" msdata:Ordinal="2" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" msdata:Ordinal="1" />
+              <xsd:attribute name="type" type="xsd:string" msdata:Ordinal="3" />
+              <xsd:attribute name="mimetype" type="xsd:string" msdata:Ordinal="4" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="resheader">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" />
+            </xsd:complexType>
+          </xsd:element>
+        </xsd:choice>
+      </xsd:complexType>
+    </xsd:element>
+  </xsd:schema>
+  <resheader name="resmimetype">
+    <value>text/microsoft-resx</value>
+  </resheader>
+  <resheader name="version">
+    <value>2.0</value>
+  </resheader>
+  <resheader name="reader">
+    <value>System.Resources.ResXResourceReader, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+  <resheader name="writer">
+    <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+  <data name="SettingsTitle" xml:space="preserve">
+    <value>CursorLang — Настройки</value>
+  </data>
+  <data name="TrayMenuSettings" xml:space="preserve">
+    <value>Настройки</value>
+  </data>
+  <data name="TrayMenuExit" xml:space="preserve">
+    <value>Выход</value>
+  </data>
+  <data name="SectionInterface" xml:space="preserve">
+    <value>Интерфейс</value>
+  </data>
+  <data name="LanguageLabel" xml:space="preserve">
+    <value>Язык интерфейса</value>
+  </data>
+  <data name="ThemeLabel" xml:space="preserve">
+    <value>Тема</value>
+  </data>
+  <data name="AppTheme_System" xml:space="preserve">
+    <value>Как в Windows</value>
+  </data>
+  <data name="AppTheme_Light" xml:space="preserve">
+    <value>Светлая</value>
+  </data>
+  <data name="AppTheme_Dark" xml:space="preserve">
+    <value>Тёмная</value>
+  </data>
+  <data name="SectionPlacement" xml:space="preserve">
+    <value>Расположение</value>
+  </data>
+  <data name="PlacementModeLabel" xml:space="preserve">
+    <value>Режим</value>
+  </data>
+  <data name="PopupPlacementMode_AtCursor" xml:space="preserve">
+    <value>Рядом с курсором</value>
+  </data>
+  <data name="PopupPlacementMode_AtCaret" xml:space="preserve">
+    <value>Рядом с кареткой ввода</value>
+  </data>
+  <data name="PopupPlacementMode_FixedPoint" xml:space="preserve">
+    <value>В заданной точке экрана</value>
+  </data>
+  <data name="CursorCornerLabel" xml:space="preserve">
+    <value>Сторона</value>
+  </data>
+  <data name="AnchorSide_BottomRight" xml:space="preserve">
+    <value>Справа снизу</value>
+  </data>
+  <data name="AnchorSide_BottomLeft" xml:space="preserve">
+    <value>Слева снизу</value>
+  </data>
+  <data name="AnchorSide_TopRight" xml:space="preserve">
+    <value>Справа сверху</value>
+  </data>
+  <data name="AnchorSide_TopLeft" xml:space="preserve">
+    <value>Слева сверху</value>
+  </data>
+  <data name="AnchorSide_Left" xml:space="preserve">
+    <value>Слева</value>
+  </data>
+  <data name="AnchorSide_Right" xml:space="preserve">
+    <value>Справа</value>
+  </data>
+  <data name="CursorOffsetLabel" xml:space="preserve">
+    <value>Отступ</value>
+  </data>
+  <data name="ScreenPositionLabel" xml:space="preserve">
+    <value>Позиция на экране</value>
+  </data>
+  <data name="ScreenPosition_TopLeft" xml:space="preserve">
+    <value>Слева сверху</value>
+  </data>
+  <data name="ScreenPosition_Top" xml:space="preserve">
+    <value>Сверху по центру</value>
+  </data>
+  <data name="ScreenPosition_Bottom" xml:space="preserve">
+    <value>Снизу по центру</value>
+  </data>
+  <data name="ScreenPosition_TopRight" xml:space="preserve">
+    <value>Справа сверху</value>
+  </data>
+  <data name="ScreenPosition_BottomLeft" xml:space="preserve">
+    <value>Слева снизу</value>
+  </data>
+  <data name="ScreenPosition_BottomRight" xml:space="preserve">
+    <value>Справа снизу</value>
+  </data>
+  <data name="ScreenPosition_Center" xml:space="preserve">
+    <value>По центру</value>
+  </data>
+  <data name="ScreenMarginLabel" xml:space="preserve">
+    <value>Отступ от края экрана</value>
+  </data>
+  <data name="SectionAppearance" xml:space="preserve">
+    <value>Внешний вид</value>
+  </data>
+  <data name="FontSizeLabel" xml:space="preserve">
+    <value>Размер шрифта</value>
+  </data>
+  <data name="OpacityLabel" xml:space="preserve">
+    <value>Прозрачность</value>
+  </data>
+  <data name="BackgroundColorLabel" xml:space="preserve">
+    <value>Цвет фона</value>
+  </data>
+  <data name="TextColorLabel" xml:space="preserve">
+    <value>Цвет текста</value>
+  </data>
+  <data name="SectionBehavior" xml:space="preserve">
+    <value>Поведение</value>
+  </data>
+  <data name="DurationLabel" xml:space="preserve">
+    <value>Время отображения</value>
+  </data>
+  <data name="PreviewLabel" xml:space="preserve">
+    <value>Предпросмотр</value>
+  </data>
+  <data name="MillisecondsSuffix" xml:space="preserve">
+    <value>мс</value>
+  </data>
+  <data name="CapsLockLabel" xml:space="preserve">
+    <value>Caps Lock</value>
+  </data>
+  <data name="CapsLockHotkeyCheck" xml:space="preserve">
+    <value>Переключать раскладку вместо смены регистра</value>
+  </data>
+  <data name="CapsLockHoldLabel" xml:space="preserve">
+    <value>Порог удержания</value>
+  </data>
+  <data name="CapsLockHoldHint" xml:space="preserve">
+    <value>Более долгое нажатие показывает подсказку и не переключает раскладку.</value>
+  </data>
+  <data name="MoreInfoLink" xml:space="preserve">
+    <value>Подробнее</value>
+  </data>
+  <data name="CapsLockElevationHint" xml:space="preserve">
+    <value>Пока в фокусе окно, запущенное от имени администратора, — диспетчер задач, редактор реестра, запрос UAC — сочетание не сработает: там Windows не отдаёт нажатия обычным приложениям. Сама подсказка показывается везде.</value>
+  </data>
+  <data name="StartupLabel" xml:space="preserve">
+    <value>Автозапуск</value>
+  </data>
+  <data name="StartupCheck" xml:space="preserve">
+    <value>Запускать вместе с Windows</value>
+  </data>
+  <data name="StartupLockedHint" xml:space="preserve">
+    <value>Автозапуском этого приложения теперь распоряжается Windows: «Параметры» — «Приложения» — «Автозагрузка».</value>
+  </data>
+  <data name="SectionUpdates" xml:space="preserve">
+    <value>Обновления</value>
+  </data>
+  <data name="CurrentVersionLabel" xml:space="preserve">
+    <value>Установленная версия</value>
+  </data>
+  <data name="CheckUpdatesButton" xml:space="preserve">
+    <value>Проверить обновления</value>
+  </data>
+  <data name="UpdateAutoCheck" xml:space="preserve">
+    <value>Проверять обновления</value>
+  </data>
+  <data name="UpdateChecking" xml:space="preserve">
+    <value>Идёт проверка обновлений…</value>
+  </data>
+  <data name="UpdateUpToDate" xml:space="preserve">
+    <value>Установлена последняя версия.</value>
+  </data>
+  <data name="UpdateAvailable" xml:space="preserve">
+    <value>Доступна версия {0}.</value>
+  </data>
+  <data name="UpdateDownloading" xml:space="preserve">
+    <value>Идёт загрузка пакета…</value>
+  </data>
+  <data name="UpdateReady" xml:space="preserve">
+    <value>Пакет скачан.</value>
+  </data>
+  <data name="UpdateFailed" xml:space="preserve">
+    <value>Не удалось обратиться к выпускам. Проверьте подключение и повторите попытку.</value>
+  </data>
+  <data name="DownloadUpdateButton" xml:space="preserve">
+    <value>Скачать</value>
+  </data>
+  <data name="InstallUpdateButton" xml:space="preserve">
+    <value>Установить</value>
+  </data>
+  <data name="ReleasePageLink" xml:space="preserve">
+    <value>Страница выпуска</value>
+  </data>
+  <data name="UpdateInstallHint" xml:space="preserve">
+    <value>Windows покажет пакет и попросит подтвердить установку. Новая версия начнёт работать после перезапуска приложения.</value>
+  </data>
+</root>

CursorLang.Core/Services/AgentExecutable.cs

@@ -0,0 +1,35 @@
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Where the background half of the application lives on disk.
+/// </summary>
+/// <remarks>
+/// Two processes now share one folder, and each of them at some point needs the path
+/// of the other: the settings window registers the agent for startup and must not
+/// register itself, and the agent starts the settings window from the tray menu.
+/// <c>Environment.ProcessPath</c> answers the wrong question for both, so the paths
+/// are worked out from the folder the assemblies were loaded from.
+/// </remarks>
+internal static class AgentExecutable
+{
+    /// <summary>The background process — the one Windows starts at sign-in.</summary>
+    internal const string AgentFileName = "CursorLang.exe";
+
+    /// <summary>The settings window, started on demand and gone when closed.</summary>
+    internal const string SettingsFileName = "CursorLang.Settings.exe";
+
+    /// <summary>
+    /// The full path of the agent, or <c>null</c> when it is not next to us — which
+    /// happens in the tests and would happen to a half-copied installation.
+    /// </summary>
+    internal static string? AgentPath => Beside(AgentFileName);
+
+    /// <summary>The full path of the settings window, on the same terms.</summary>
+    internal static string? SettingsPath => Beside(SettingsFileName);
+
+    private static string? Beside(string fileName)
+    {
+        string path = Path.Combine(AppContext.BaseDirectory, fileName);
+        return File.Exists(path) ? path : null;
+    }
+}

CursorLang.Core/Services/CapsLockSwitchCoordinator.cs

@@ -0,0 +1,77 @@
+using System.ComponentModel;
+using CursorLang.Core.Models;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Turns Caps Lock presses into actions: a short one switches the layout, a long one
+/// only shows the popup. It also turns the hook on and off following the checkbox in
+/// the settings.
+/// </summary>
+public sealed class CapsLockSwitchCoordinator : IDisposable
+{
+    private readonly ICapsLockHotkeyService _hotkeyService;
+    private readonly IKeyboardLayoutService _layoutService;
+    private readonly ILayoutPopupService _popupService;
+    private readonly AppSettings _settings;
+
+    public CapsLockSwitchCoordinator(
+        ICapsLockHotkeyService hotkeyService,
+        IKeyboardLayoutService layoutService,
+        ILayoutPopupService popupService,
+        AppSettings settings)
+    {
+        _hotkeyService = hotkeyService;
+        _layoutService = layoutService;
+        _popupService = popupService;
+        _settings = settings;
+    }
+
+    public void Start()
+    {
+        _hotkeyService.Tapped += OnTapped;
+        _hotkeyService.HoldStarted += OnHoldStarted;
+        _hotkeyService.HoldEnded += OnHoldEnded;
+        _settings.PropertyChanged += OnSettingsChanged;
+
+        ApplySetting();
+    }
+
+    public void Dispose()
+    {
+        _settings.PropertyChanged -= OnSettingsChanged;
+        _hotkeyService.Tapped -= OnTapped;
+        _hotkeyService.HoldStarted -= OnHoldStarted;
+        _hotkeyService.HoldEnded -= OnHoldEnded;
+        _hotkeyService.Stop();
+    }
+
+    private void OnSettingsChanged(object? sender, PropertyChangedEventArgs e)
+    {
+        if (e.PropertyName == nameof(AppSettings.UseCapsLockHotkey))
+        {
+            ApplySetting();
+        }
+    }
+
+    private void ApplySetting()
+    {
+        if (_settings.UseCapsLockHotkey)
+        {
+            _hotkeyService.Start();
+        }
+        else
+        {
+            _hotkeyService.Stop();
+        }
+    }
+
+    private void OnTapped(object? sender, EventArgs e) => _layoutService.SwitchToNext();
+
+    // We do not change the layout, but staying silent will not do either: without the
+    // popup a long press looks as if the key simply did not work
+    private void OnHoldStarted(object? sender, EventArgs e) =>
+        _popupService.ShowUntilHidden(_layoutService.Current);
+
+    private void OnHoldEnded(object? sender, EventArgs e) => _popupService.Hide();
+}

CursorLang.Core/Services/ColorJsonConverter.cs

@@ -0,0 +1,56 @@
+using System.Drawing;
+using System.Globalization;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Reads and writes a colour as "#AARRGGBB".
+/// </summary>
+/// <remarks>
+/// That is the form earlier versions wrote, when the colours were WPF ones and
+/// <c>Color.ToString()</c> produced it, so files already on disk keep working. The
+/// parsing is done here rather than by <c>ColorConverter</c> because that one lives in
+/// PresentationCore, and Core is read by the agent. Named colours are accepted too:
+/// nothing writes them, but the file is plain text and people edit it by hand.
+/// </remarks>
+internal sealed class ColorJsonConverter : JsonConverter<Color>
+{
+    public override Color Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+    {
+        string? value = reader.GetString();
+        if (string.IsNullOrWhiteSpace(value))
+        {
+            return Color.Black;
+        }
+
+        value = value.Trim();
+
+        if (!value.StartsWith('#'))
+        {
+            Color named = Color.FromName(value);
+
+            // Unpacked back into a plain colour on purpose: a known colour carries its
+            // name with it and does not compare equal to the same bytes written in hex,
+            // which would make "Red" and "#FFFF0000" two different settings
+            return named.IsKnownColor ? Color.FromArgb(named.ToArgb()) : Color.Black;
+        }
+
+        ReadOnlySpan<char> digits = value.AsSpan(1);
+        if (!uint.TryParse(digits, NumberStyles.HexNumber, CultureInfo.InvariantCulture, out uint packed))
+        {
+            return Color.Black;
+        }
+
+        return digits.Length switch
+        {
+            6 => Color.FromArgb((int)(packed | 0xFF000000)),
+            8 => Color.FromArgb((int)packed),
+            _ => Color.Black,
+        };
+    }
+
+    public override void Write(Utf8JsonWriter writer, Color value, JsonSerializerOptions options) =>
+        writer.WriteStringValue($"#{value.A:X2}{value.R:X2}{value.G:X2}{value.B:X2}");
+}

CursorLang.Core/Services/GiteaReleaseFeed.cs

@@ -0,0 +1,227 @@
+using System.Net.Http.Headers;
+using System.Runtime.InteropServices;
+using System.Text.Json;
+using CursorLang.Core.Models;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Gitea releases.
+/// </summary>
+/// <remarks>
+/// The service address is the address of the server itself — "https://git.example.com/":
+/// the Gitea API lives on the same host as the repository pages.
+/// </remarks>
+internal sealed class GiteaReleaseFeed : IReleaseFeed
+{
+    /// <summary>
+    /// How many releases to ask the server for. It returns them newest first, but the
+    /// newest one may turn out to have no package — when the build has not been
+    /// published yet, for instance — so a small reserve is taken.
+    /// </summary>
+    private const int PageSize = 10;
+
+    /// <summary>
+    /// A response with the release list is a few kilobytes of text. There is no point
+    /// waiting longer: the check runs in the background, and a failed one bothers nobody.
+    /// </summary>
+    private static readonly TimeSpan RequestTimeout = TimeSpan.FromSeconds(20);
+
+    private readonly HttpClient _client;
+    private readonly UpdateOptions _options;
+
+    public GiteaReleaseFeed(HttpClient client, UpdateOptions options)
+    {
+        _client = client;
+        _options = options;
+    }
+
+    /// <summary>
+    /// How the architecture is spelled in the file names built by
+    /// <c>build-msix.ps1</c>: <c>CursorLang-1.0.0.0-x64.msix</c>.
+    /// </summary>
+    private static string ArchitectureName => RuntimeInformation.ProcessArchitecture == Architecture.Arm64
+        ? "arm64"
+        : "x64";
+
+    public async Task<ReleaseInfo?> GetLatestAsync(CancellationToken cancellationToken)
+    {
+        using var timeout = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
+        timeout.CancelAfter(RequestTimeout);
+
+        using var request = new HttpRequestMessage(HttpMethod.Get, BuildReleasesUri());
+        Authorize(request);
+
+        using HttpResponseMessage response = await _client.SendAsync(
+            request, HttpCompletionOption.ResponseHeadersRead, timeout.Token);
+        response.EnsureSuccessStatusCode();
+
+        await using Stream stream = await response.Content.ReadAsStreamAsync(timeout.Token);
+        using JsonDocument document = await JsonDocument.ParseAsync(stream, cancellationToken: timeout.Token);
+
+        if (document.RootElement.ValueKind != JsonValueKind.Array)
+        {
+            return null;
+        }
+
+        // The order of the releases is up to the server, while what we need is the
+        // highest version number: a fix released for an old branch may well be the newest one
+        return document.RootElement.EnumerateArray()
+            .Select(Read)
+            .OfType<ReleaseInfo>()
+            .MaxBy(release => release.Version);
+    }
+
+    public void Authorize(HttpRequestMessage request)
+    {
+        if (!string.IsNullOrWhiteSpace(_options.AccessToken))
+        {
+            // "token" is the Gitea scheme of its own for access keys; "Bearer" is not
+            // understood by every version, while this one has been there since the API appeared
+            request.Headers.Authorization = new AuthenticationHeaderValue("token", _options.AccessToken);
+        }
+    }
+
+    /// <summary>
+    /// Parses a single release. <c>null</c> means the release will not do: a draft,
+    /// a prerelease or a release without a package.
+    /// </summary>
+    private static ReleaseInfo? Read(JsonElement release)
+    {
+        // A draft is visible only to whoever created it, and the application does not
+        // offer a prerelease: those are sought out deliberately
+        if (ReadFlag(release, "draft") || ReadFlag(release, "prerelease"))
+        {
+            return null;
+        }
+
+        Version? version = ParseTag(ReadString(release, "tag_name"));
+        if (version is null)
+        {
+            return null;
+        }
+
+        if (!release.TryGetProperty("assets", out JsonElement assets) || assets.ValueKind != JsonValueKind.Array)
+        {
+            return null;
+        }
+
+        ReleaseAsset? package = PickPackage(assets.EnumerateArray().Select(ReadAsset).OfType<ReleaseAsset>());
+        if (package is null)
+        {
+            return null;
+        }
+
+        return new ReleaseInfo(
+            version,
+            ReadString(release, "tag_name") ?? version.ToString(),
+            ReadUri(release, "html_url"),
+            package);
+    }
+
+    private static ReleaseAsset? ReadAsset(JsonElement asset)
+    {
+        string? name = ReadString(asset, "name");
+        Uri? url = ReadUri(asset, "browser_download_url");
+
+        if (string.IsNullOrWhiteSpace(name) || url is null)
+        {
+            return null;
+        }
+
+        long size = asset.TryGetProperty("size", out JsonElement value) && value.TryGetInt64(out long bytes)
+            ? bytes
+            : 0;
+
+        return new ReleaseAsset(name, url, size);
+    }
+
+    /// <summary>
+    /// The version from a tag. "1.2.3" and "v1.2.3" are understood; a tag with
+    /// anything besides numbers — "v1.2.3-beta" — counts as a prerelease and is
+    /// skipped: the application does not offer such versions on its own.
+    /// </summary>
+    private static Version? ParseTag(string? tag)
+    {
+        if (string.IsNullOrWhiteSpace(tag))
+        {
+            return null;
+        }
+
+        ReadOnlySpan<char> numbers = tag.AsSpan().Trim().TrimStart("vV");
+
+        foreach (char symbol in numbers)
+        {
+            if (!char.IsAsciiDigit(symbol) && symbol != '.')
+            {
+                return null;
+            }
+        }
+
+        if (!Version.TryParse(numbers, out Version? version))
+        {
+            return null;
+        }
+
+        // In a tag such as "v1.2" the lower parts are not set at all, yet comparing
+        // them with the version of the installed package calls for zeros
+        return new Version(
+            version.Major,
+            version.Minor,
+            Math.Max(version.Build, 0),
+            Math.Max(version.Revision, 0));
+    }
+
+    /// <summary>
+    /// Picks the attached file the application updates itself with.
+    /// </summary>
+    private static ReleaseAsset? PickPackage(IEnumerable<ReleaseAsset> assets)
+    {
+        // An unencrypted connection is out right away: Windows will check the package
+        // signature by itself, but a substituted file is not even worth downloading
+        ReleaseAsset[] packages = [.. assets.Where(asset => asset.Url.Scheme == Uri.UriSchemeHttps)];
+
+        ReleaseAsset? bundle = packages.FirstOrDefault(
+            asset => asset.FileName.EndsWith(".msixbundle", StringComparison.OrdinalIgnoreCase));
+
+        if (bundle is not null)
+        {
+            // A bundle carries both architectures, so there is nothing to choose between
+            return bundle;
+        }
+
+        ReleaseAsset[] single = [.. packages.Where(
+            asset => asset.FileName.EndsWith(".msix", StringComparison.OrdinalIgnoreCase))];
+
+        ReleaseAsset? matching = single.FirstOrDefault(
+            asset => asset.FileName.Contains(ArchitectureName, StringComparison.OrdinalIgnoreCase));
+
+        // A package without an architecture in its name will do only when it is the
+        // only one: otherwise it is unclear which of them is for this machine
+        return matching ?? (single.Length == 1 ? single[0] : null);
+    }
+
+    private static string? ReadString(JsonElement element, string name) =>
+        element.TryGetProperty(name, out JsonElement value) && value.ValueKind == JsonValueKind.String
+            ? value.GetString()
+            : null;
+
+    private static Uri? ReadUri(JsonElement element, string name) =>
+        Uri.TryCreate(ReadString(element, name), UriKind.Absolute, out Uri? uri) ? uri : null;
+
+    private static bool ReadFlag(JsonElement element, string name) =>
+        element.TryGetProperty(name, out JsonElement value) && value.ValueKind == JsonValueKind.True;
+
+    /// <summary>
+    /// The address the server returns the release list at. The trailing slash matters:
+    /// without it <c>Uri</c> drops the last part of the address, and
+    /// "https://host/gitea" would have turned into "https://host/api/...".
+    /// </summary>
+    private Uri BuildReleasesUri()
+    {
+        string service = _options.ServiceUri.AbsoluteUri;
+        string path = $"api/v1/repos/{_options.Project.Trim('/')}/releases?limit={PageSize}";
+
+        return new Uri(service.EndsWith('/') ? service + path : $"{service}/{path}");
+    }
+}

CursorLang.Core/Services/ICapsLockHotkeyService.cs

@@ -0,0 +1,29 @@
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Intercepts Caps Lock at the system level and splits the presses into short and
+/// long ones. What to do with them is up to the subscribers.
+/// </summary>
+public interface ICapsLockHotkeyService
+{
+    /// <summary>A short press: the key was released before the hold threshold.</summary>
+    event EventHandler? Tapped;
+
+    /// <summary>The hold threshold has passed, the key is still held.</summary>
+    event EventHandler? HoldStarted;
+
+    /// <summary>The hold is over: the key was released.</summary>
+    event EventHandler? HoldEnded;
+
+    /// <summary>Whether the hook is installed right now.</summary>
+    bool IsRunning { get; }
+
+    /// <summary>
+    /// Starts intercepting. Must be called from the user interface thread:
+    /// a system keyboard hook works only on a thread with a message loop.
+    /// </summary>
+    void Start();
+
+    /// <summary>Removes the hook, giving the key its usual behaviour back.</summary>
+    void Stop();
+}

CursorLang.Core/Services/IKeyboardLayoutService.cs

@@ -0,0 +1,21 @@
+using CursorLang.Core.Models;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Tracks the layout of the active window — including in other applications —
+/// and can switch it.
+/// </summary>
+public interface IKeyboardLayoutService
+{
+    /// <summary>The layout of the active window at the moment.</summary>
+    KeyboardLayout Current { get; }
+
+    event EventHandler<LayoutChangedEventArgs>? LayoutChanged;
+
+    void Start();
+
+    void Stop();
+
+    void SwitchToNext();
+}

CursorLang.Core/Services/ILayoutPopupService.cs

@@ -0,0 +1,20 @@
+using CursorLang.Core.Models;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Shows the layout popup at the cursor.
+/// </summary>
+public interface ILayoutPopupService
+{
+    /// <summary>Shows the popup and takes it down after the time set in the settings.</summary>
+    void Show(KeyboardLayout layout);
+
+    /// <summary>
+    /// Shows the popup until <see cref="Hide"/> is called explicitly: needed where the
+    /// show time is set by a user action rather than by a timer.
+    /// </summary>
+    void ShowUntilHidden(KeyboardLayout layout);
+
+    void Hide();
+}

CursorLang.Core/Services/ILayoutPopupWindow.cs

@@ -0,0 +1,28 @@
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// The popup window as seen by whoever decides when it is shown.
+/// </summary>
+/// <remarks>
+/// The window picks its place and size itself, and only three actions are needed from
+/// it on the outside. The tests check the work of the popup service through the same
+/// interface: there is no point bringing up a real window to check a timer.
+/// </remarks>
+public interface ILayoutPopupWindow
+{
+    /// <summary>
+    /// Shows the window with the given text at the place set by the settings.
+    /// </summary>
+    /// <remarks>
+    /// The text is passed in rather than bound: there is no view model behind the
+    /// window any more, and no data binding either — it is a Win32 window that paints
+    /// one line of text itself.
+    /// </remarks>
+    void ShowPopup(string shortName);
+
+    /// <summary>Takes the window off the screen without destroying it.</summary>
+    void Hide();
+
+    /// <summary>Closes the window for good.</summary>
+    void Close();
+}

CursorLang.Core/Services/ILocalizationService.cs

@@ -0,0 +1,25 @@
+using System.ComponentModel;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>An interface language to choose from in the settings.</summary>
+/// <param name="Code">The culture code: "ru", "en".</param>
+/// <param name="DisplayName">The name in that very language.</param>
+public sealed record LanguageOption(string Code, string DisplayName)
+{
+    // Accessibility tools take the name of the list item from here
+    public override string ToString() => DisplayName;
+}
+
+/// <summary>
+/// Provides the interface strings and can change the language without a restart.
+/// </summary>
+public interface ILocalizationService : INotifyPropertyChanged
+{
+    /// <summary>The string for a resource key. Bindings update when the language changes.</summary>
+    string this[string key] { get; }
+
+    IReadOnlyList<LanguageOption> AvailableLanguages { get; }
+
+    string CurrentLanguage { get; set; }
+}

CursorLang.Core/Services/IReleaseFeed.cs

@@ -0,0 +1,21 @@
+using CursorLang.Core.Models;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// The release list of the repository.
+/// </summary>
+public interface IReleaseFeed
+{
+    /// <summary>
+    /// Returns the newest release carrying an MSIX package, or <c>null</c>
+    /// when there is no suitable release.
+    /// </summary>
+    Task<ReleaseInfo?> GetLatestAsync(CancellationToken cancellationToken);
+
+    /// <summary>
+    /// Adds to the request whatever a private repository needs. The package is
+    /// downloaded not by the list itself, but access to it is closed just the same.
+    /// </summary>
+    void Authorize(HttpRequestMessage request);
+}

CursorLang.Core/Services/IStartupService.cs

@@ -0,0 +1,18 @@
+using CursorLang.Core.Models;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Starting the app together with Windows.
+/// </summary>
+public interface IStartupService
+{
+    /// <summary>Finds out the current state of startup.</summary>
+    Task<StartupState> GetStateAsync();
+
+    /// <summary>
+    /// Asks for startup to be switched on or off and answers with the state that
+    /// came of it: the request to switch it on may well be turned down.
+    /// </summary>
+    Task<StartupState> SetEnabledAsync(bool enabled);
+}

CursorLang.Core/Services/IUpdateService.cs

@@ -0,0 +1,40 @@
+using CursorLang.Core.Models;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Checking for and installing new versions of the application.
+/// </summary>
+public interface IUpdateService
+{
+    /// <summary>
+    /// It makes sense for this installation to update itself.
+    /// </summary>
+    /// <remarks>
+    /// An application installed from the Store is updated by the Store itself:
+    /// offering a package from elsewhere on top of it will not do — Windows would
+    /// not accept it anyway.
+    /// </remarks>
+    bool IsSupported { get; }
+
+    /// <summary>The version of the running application.</summary>
+    Version CurrentVersion { get; }
+
+    /// <summary>
+    /// Looks for a release newer than the installed one. <c>null</c> means the latest
+    /// version is installed or there is no suitable release in the repository.
+    /// </summary>
+    Task<ReleaseInfo?> CheckAsync(CancellationToken cancellationToken);
+
+    /// <summary>
+    /// Downloads the release package and returns the path to it.
+    /// </summary>
+    /// <remarks>
+    /// <c>progress</c> receives the downloaded fraction from 0 to 1. While the file
+    /// size is unknown — not every hosting reports it — there will be no calls at all.
+    /// </remarks>
+    Task<string> DownloadAsync(ReleaseInfo release, IProgress<double>? progress, CancellationToken cancellationToken);
+
+    /// <summary>Hands the downloaded package over to the Windows app installer.</summary>
+    void Install(string packagePath);
+}

CursorLang.Core/Services/KeyboardLayoutService.cs

@@ -0,0 +1,179 @@
+using CursorLang.Core.Interop;
+using CursorLang.Core.Models;
+using CursorLang.Core.Threading;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// The settings of layout tracking.
+/// </summary>
+public sealed class KeyboardLayoutOptions
+{
+    /// <summary>How often to check the layout of the active window.</summary>
+    public TimeSpan PollInterval { get; init; } = TimeSpan.FromMilliseconds(150);
+
+    /// <summary>
+    /// How long to wait for a layout that has just changed to stop changing.
+    /// </summary>
+    /// <remarks>
+    /// Short on purpose: it is added to the delay before the popup shows, and it only
+    /// applies while a switch is in flight. See the settling in
+    /// <see cref="KeyboardLayoutService"/>.
+    /// </remarks>
+    public TimeSpan SettleInterval { get; init; } = TimeSpan.FromMilliseconds(40);
+}
+
+/// <summary>
+/// Polls the active window on a timer.
+/// </summary>
+/// <remarks>
+/// Polling was chosen not for simplicity: there is no event-based way to learn about
+/// a layout change in another process from managed code. HSHELL_LANGUAGE from
+/// RegisterShellHookWindow does not arrive on Windows 10/11, and TSF notifications
+/// (ITfLanguageProfileNotifySink) report only language changes inside our own process
+/// — both options were tried and did not work. One tick is three Win32 calls reading
+/// data from kernel memory.
+///
+/// The timer ticks on the message loop of whatever thread starts it, the same as a
+/// dispatcher timer did: the agent has a plain Win32 loop and no dispatcher to offer.
+///
+/// A switch is not reported the moment it is first seen but once the value has stopped
+/// moving. A layout change is rarely a single step: the language switcher of Windows
+/// takes the focus while it is up, and applications with a rendering engine of their
+/// own change the layout of a helper thread before that of the input window. Polling
+/// catches those in-between values, and reporting them meant the popup appearing with
+/// one layout and turning into another in front of the user.
+///
+/// The price is that the popup comes up one short tick later. While a switch is in
+/// flight the timer runs at <see cref="KeyboardLayoutOptions.SettleInterval"/> rather
+/// than at the polling interval, so that tick is a few tens of milliseconds and not
+/// another whole poll.
+/// </remarks>
+public sealed class KeyboardLayoutService : IKeyboardLayoutService, IDisposable
+{
+    private readonly MessageTimer _pollTimer;
+    private readonly Func<IntPtr> _getForegroundWindow;
+    private readonly Func<int> _getActiveLocaleId;
+    private readonly Action _requestNextLayout;
+    private readonly KeyboardLayoutOptions _options;
+
+    private int _lastLocaleId = -1;
+    private IntPtr _lastForegroundWindow;
+    private int _settlingLocaleId = -1;
+
+    public KeyboardLayoutService(KeyboardLayoutOptions options)
+        : this(
+            options,
+            KeyboardLayoutNative.GetForegroundWindow,
+            KeyboardLayoutNative.GetActiveLocaleId,
+            KeyboardLayoutNative.RequestNextLayout)
+    {
+    }
+
+    /// <summary>
+    /// Takes the sources of system information explicitly: in tests the layout and the
+    /// active window are not provided by Windows.
+    /// </summary>
+    internal KeyboardLayoutService(
+        KeyboardLayoutOptions options,
+        Func<IntPtr> getForegroundWindow,
+        Func<int> getActiveLocaleId,
+        Action requestNextLayout)
+    {
+        _getForegroundWindow = getForegroundWindow;
+        _getActiveLocaleId = getActiveLocaleId;
+        _requestNextLayout = requestNextLayout;
+        _options = options;
+
+        _pollTimer = new MessageTimer { Interval = options.PollInterval };
+        _pollTimer.Tick += OnTick;
+    }
+
+    public event EventHandler<LayoutChangedEventArgs>? LayoutChanged;
+
+    public KeyboardLayout Current => KeyboardLayout.FromLocaleId(_getActiveLocaleId());
+
+    public void Start()
+    {
+        _lastForegroundWindow = _getForegroundWindow();
+        _lastLocaleId = _getActiveLocaleId();
+        _settlingLocaleId = -1;
+        _pollTimer.Interval = _options.PollInterval;
+        _pollTimer.Start();
+    }
+
+    public void Stop() => _pollTimer.Stop();
+
+    public void SwitchToNext() => _requestNextLayout();
+
+    public void Dispose()
+    {
+        _pollTimer.Tick -= OnTick;
+        _pollTimer.Dispose();
+    }
+
+    private void OnTick(object? sender, EventArgs e) => Poll();
+
+    // A single poll step. Called by the timer, and in tests — directly:
+    // there is no point waiting for a tick to check how the reason for a layout
+    // change is decided
+    internal void Poll()
+    {
+        IntPtr foreground = _getForegroundWindow();
+        if (foreground == IntPtr.Zero)
+        {
+            return;
+        }
+
+        int localeId = _getActiveLocaleId();
+        if (localeId == _lastLocaleId)
+        {
+            _lastForegroundWindow = foreground;
+            Settle(inFlight: false);
+
+            return;
+        }
+
+        if (localeId != _settlingLocaleId)
+        {
+            _settlingLocaleId = localeId;
+            Settle(inFlight: true);
+
+            return;
+        }
+
+        bool appSwitched = foreground != _lastForegroundWindow;
+
+        _lastLocaleId = localeId;
+        _lastForegroundWindow = foreground;
+        Settle(inFlight: false);
+
+        // Moving to another application with a layout of its own is not the same as
+        // the user switching the layout, and the subscribers are free to react to
+        // these cases differently
+        LayoutChangeReason reason = appSwitched
+            ? LayoutChangeReason.ApplicationSwitched
+            : LayoutChangeReason.UserSwitched;
+
+        LayoutChanged?.Invoke(this, new LayoutChangedEventArgs(KeyboardLayout.FromLocaleId(localeId), reason));
+    }
+
+    // While a switch is in flight the next look comes sooner: that wait is added to the
+    // delay before the popup, and a whole polling interval there would be felt
+    private void Settle(bool inFlight)
+    {
+        if (!inFlight)
+        {
+            _settlingLocaleId = -1;
+        }
+
+        TimeSpan wanted = inFlight ? _options.SettleInterval : _options.PollInterval;
+        if (_pollTimer.Interval == wanted || !_pollTimer.IsRunning)
+        {
+            return;
+        }
+
+        _pollTimer.Interval = wanted;
+        _pollTimer.Start();
+    }
+}

CursorLang.Core/Services/LayoutNotificationCoordinator.cs

@@ -0,0 +1,41 @@
+using CursorLang.Core.Models;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Ties layout tracking to showing the popup.
+/// Lives for as long as the application runs, regardless of the open windows.
+/// </summary>
+public sealed class LayoutNotificationCoordinator : IDisposable
+{
+    private readonly IKeyboardLayoutService _layoutService;
+    private readonly ILayoutPopupService _popupService;
+
+    public LayoutNotificationCoordinator(IKeyboardLayoutService layoutService, ILayoutPopupService popupService)
+    {
+        _layoutService = layoutService;
+        _popupService = popupService;
+    }
+
+    public void Start()
+    {
+        _layoutService.LayoutChanged += OnLayoutChanged;
+        _layoutService.Start();
+    }
+
+    public void Dispose()
+    {
+        _layoutService.LayoutChanged -= OnLayoutChanged;
+        _layoutService.Stop();
+    }
+
+    private void OnLayoutChanged(object? sender, LayoutChangedEventArgs e)
+    {
+        // When moving to another application the layout changes without the user
+        // taking part, and a popup would be intrusive
+        if (e.Reason == LayoutChangeReason.UserSwitched)
+        {
+            _popupService.Show(e.Layout);
+        }
+    }
+}

CursorLang.Core/Services/LocalizationService.cs

@@ -0,0 +1,58 @@
+using System.Globalization;
+using System.Resources;
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Takes the strings from the resources and, when the language changes, asks WPF to
+/// re-read every binding.
+/// </summary>
+/// <remarks>
+/// Both processes use it: the settings window for its whole interface, the agent for
+/// the three captions of the tray menu. The theme no longer reaches that menu — Windows
+/// draws it — but the language still does.
+/// </remarks>
+public sealed class LocalizationService : ObservableObject, ILocalizationService
+{
+    /// <summary>
+    /// The name WPF reports when an indexer changes. Spelt out rather than taken from
+    /// <c>Binding.IndexerName</c>: that constant lives in PresentationFramework, and
+    /// Core is read by the agent, which does not load WPF.
+    /// </summary>
+    public const string IndexerName = "Item[]";
+
+    private static readonly ResourceManager Resources =
+        new("CursorLang.Core.Resources.Strings", typeof(LocalizationService).Assembly);
+
+    private CultureInfo _culture = CultureInfo.GetCultureInfo("en");
+
+    public string this[string key] => Resources.GetString(key, _culture) ?? key;
+
+    public IReadOnlyList<LanguageOption> AvailableLanguages { get; } =
+    [
+        new LanguageOption("en", "English"),
+        new LanguageOption("ru", "Русский"),
+    ];
+
+    public string CurrentLanguage
+    {
+        get => _culture.TwoLetterISOLanguageName;
+        set
+        {
+            if (string.IsNullOrWhiteSpace(value) || value == CurrentLanguage)
+            {
+                return;
+            }
+
+            _culture = CultureInfo.GetCultureInfo(value);
+            CultureInfo.CurrentUICulture = _culture;
+
+            OnPropertyChanged(nameof(CurrentLanguage));
+
+            // We report a change of the indexer: that is how every binding of the
+            // {Binding Localization[Key]} kind updates, that is, all the interface text
+            OnPropertyChanged(IndexerName);
+        }
+    }
+}

CursorLang.Core/Services/PopupLayout.cs

@@ -0,0 +1,95 @@
+using CursorLang.Core.Interop;
+using CursorLang.Core.Models;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Computes the screen point to show the popup at.
+/// </summary>
+/// <remarks>
+/// There is nothing but arithmetic here: where the cursor is, where the caret is and
+/// what the monitor bounds are is figured out by the window itself — it has a handle
+/// of its own for that. The computation is kept apart because it is exactly the place
+/// where a sign or half a size is easy to get wrong, and this way it can be checked
+/// without a single window on screen.
+///
+/// All the values are in physical pixels: monitors have different scaling, and
+/// converting to WPF units halfway would mean rounding twice.
+/// </remarks>
+internal static class PopupLayout
+{
+    /// <summary>
+    /// The popup position next to the anchor point — the cursor or the caret.
+    /// The cursor arrives here as a rectangle of zero size.
+    /// </summary>
+    internal static PopupWindowNative.Point NearAnchor(
+        PopupWindowNative.Rect anchor,
+        AnchorSide side,
+        int offset,
+        int width,
+        int height)
+    {
+        int toLeftOf = anchor.Left - offset - width;
+        int toRightOf = anchor.Right + offset;
+        int above = anchor.Top - offset - height;
+        int below = anchor.Bottom + offset;
+
+        // For the "left" and "right" sides the popup lines up with the anchor point
+        int middle = anchor.Top + (((anchor.Bottom - anchor.Top) - height) / 2);
+
+        (int x, int y) = side switch
+        {
+            AnchorSide.TopLeft => (toLeftOf, above),
+            AnchorSide.TopRight => (toRightOf, above),
+            AnchorSide.Left => (toLeftOf, middle),
+            AnchorSide.Right => (toRightOf, middle),
+            AnchorSide.BottomLeft => (toLeftOf, below),
+            _ => (toRightOf, below),
+        };
+
+        return new PopupWindowNative.Point { X = x, Y = y };
+    }
+
+    /// <summary>
+    /// The popup position in the given corner of the monitor work area.
+    /// </summary>
+    internal static PopupWindowNative.Point OnScreen(
+        PopupWindowNative.Rect work,
+        ScreenPosition position,
+        int margin,
+        int width,
+        int height)
+    {
+        int left = work.Left + margin;
+        int right = work.Right - margin - width;
+        int top = work.Top + margin;
+        int bottom = work.Bottom - margin - height;
+        int centerX = work.Left + ((work.Right - work.Left - width) / 2);
+        int centerY = work.Top + ((work.Bottom - work.Top - height) / 2);
+
+        (int x, int y) = position switch
+        {
+            ScreenPosition.TopLeft => (left, top),
+            ScreenPosition.Top => (centerX, top),
+            ScreenPosition.TopRight => (right, top),
+            ScreenPosition.BottomLeft => (left, bottom),
+            ScreenPosition.Bottom => (centerX, bottom),
+            ScreenPosition.BottomRight => (right, bottom),
+            _ => (centerX, centerY),
+        };
+
+        return new PopupWindowNative.Point { X = x, Y = y };
+    }
+
+    /// <summary>A rectangle of zero size at a point — the mouse cursor as an anchor.</summary>
+    internal static PopupWindowNative.Rect AsAnchor(PopupWindowNative.Point point) => new()
+    {
+        Left = point.X,
+        Top = point.Y,
+        Right = point.X,
+        Bottom = point.Y,
+    };
+
+    /// <summary>WPF units into physical pixels of a monitor with the given scale.</summary>
+    internal static int ToPixels(double wpfUnits, double scale) => (int)Math.Round(wpfUnits * scale);
+}

CursorLang.Core/Services/RegistryStartup.cs

@@ -0,0 +1,130 @@
+using System.Security;
+using CursorLang.Core.Models;
+using Microsoft.Win32;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Startup for a build that is not a package: a value under the Run key.
+/// </summary>
+/// <remarks>
+/// A package declares its startup task in the manifest and asks Windows to switch
+/// it on. A build unpacked into a folder has no manifest, so it registers itself
+/// the way desktop programs always have — under the Run key of the current user.
+/// Administrator rights are not needed for that: the key belongs to the user.
+///
+/// Windows keeps the user's own verdict apart from the entry itself. Turning the
+/// app off in Settings — Apps — Startup leaves the Run value where it is and marks
+/// it disabled under StartupApproved. The mark is obeyed here the same way a
+/// package obeys DisabledByUser: the app does not argue with the user.
+/// </remarks>
+internal sealed class RegistryStartup
+{
+    private const string RunPath = @"Software\Microsoft\Windows\CurrentVersion\Run";
+
+    private const string ApprovedPath =
+        @"Software\Microsoft\Windows\CurrentVersion\Explorer\StartupApproved\Run";
+
+    /// <summary>The name of the value — Windows shows it in the startup list.</summary>
+    private const string ValueName = "CursorLang";
+
+    private readonly RegistryKey _root;
+    private readonly string? _command;
+
+    internal RegistryStartup()
+        : this(Registry.CurrentUser, GetCommand())
+    {
+    }
+
+    /// <summary>A root of the test's own, so that the real startup list is left alone.</summary>
+    internal RegistryStartup(RegistryKey root, string? command)
+    {
+        _root = root;
+        _command = command;
+    }
+
+    internal StartupState GetState()
+    {
+        if (_command is null)
+        {
+            return StartupState.Unavailable;
+        }
+
+        try
+        {
+            using RegistryKey? run = _root.OpenSubKey(RunPath);
+
+            if (run?.GetValue(ValueName) is null)
+            {
+                return StartupState.Disabled;
+            }
+
+            return IsApprovedByUser() ? StartupState.Enabled : StartupState.DisabledByUser;
+        }
+        catch (Exception e) when (e is SecurityException or UnauthorizedAccessException or IOException)
+        {
+            return StartupState.Unavailable;
+        }
+    }
+
+    internal StartupState SetEnabled(bool enabled)
+    {
+        if (_command is null)
+        {
+            return StartupState.Unavailable;
+        }
+
+        try
+        {
+            using RegistryKey run = _root.CreateSubKey(RunPath);
+
+            if (enabled)
+            {
+                // The path is written afresh every time: the app may have been moved
+                run.SetValue(ValueName, _command, RegistryValueKind.String);
+            }
+            else
+            {
+                run.DeleteValue(ValueName, throwOnMissingValue: false);
+            }
+        }
+        catch (Exception e) when (e is SecurityException or UnauthorizedAccessException or IOException)
+        {
+            return StartupState.Unavailable;
+        }
+
+        // The answer is read back rather than assumed: an entry the user has
+        // banned stays banned no matter what was just written next to it
+        return GetState();
+    }
+
+    /// <summary>
+    /// Whether the user has left the entry alone. The verdict is a blob whose
+    /// lowest bit of the first byte stands for the ban; no value means untouched.
+    /// </summary>
+    private bool IsApprovedByUser()
+    {
+        using RegistryKey? approved = _root.OpenSubKey(ApprovedPath);
+
+        return approved?.GetValue(ValueName) is not byte[] { Length: > 0 } verdict
+            || (verdict[0] & 1) == 0;
+    }
+
+    /// <summary>
+    /// What Windows is to run. <c>null</c> — the agent is not where it should be, and
+    /// there is nothing to write down.
+    /// </summary>
+    /// <remarks>
+    /// The agent by name rather than <c>Environment.ProcessPath</c>: this setting is
+    /// switched from the settings window, and its own path would put the wrong process
+    /// into the startup list — one that shows a window and exits.
+    ///
+    /// The argument is how the agent recognises a launch of this kind and goes straight
+    /// to the tray without the settings window: see <see cref="StartupLaunch"/>. The
+    /// user starting the application themselves passes no such thing and gets the window.
+    /// </remarks>
+    internal static string? GetCommand() =>
+        AgentExecutable.AgentPath is { Length: > 0 } path
+            ? $"\"{path}\" {StartupLaunch.Argument}"
+            : null;
+}

CursorLang.Core/Services/SettingsService.cs

@@ -0,0 +1,252 @@
+using System.ComponentModel;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using CursorLang.Core.Interop;
+using CursorLang.Core.Models;
+using CursorLang.Core.Threading;
+using Windows.Storage;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Keeps the settings in the settings.json file.
+/// </summary>
+/// <remarks>
+/// The file is the whole of the connection between the two processes, and they use it
+/// from opposite ends. The settings window calls <see cref="TrackChanges"/> and is the
+/// only writer; the agent only ever reads, and re-reads when the window tells it to.
+/// A second writer would mean two processes racing for one file and an edit going missing.
+///
+/// The location depends on how the application is installed. A package from the Store
+/// keeps its settings in a folder of its own: Windows removes it together with the
+/// application, and after the removal nothing superfluous is left in the system — that
+/// is what Store applications are expected to do. A separately installed application
+/// keeps its settings in %APPDATA%, as before.
+///
+/// Settings left over from a separately installed application are picked up by the
+/// package on the first launch and moved over. The original file stays where it is:
+/// both versions can be installed side by side, and the application has no right to
+/// delete settings that are not its own.
+/// </remarks>
+public sealed class SettingsService : IDisposable
+{
+    private static readonly JsonSerializerOptions SerializerOptions = new()
+    {
+        WriteIndented = true,
+        Converters = { new ColorJsonConverter(), new JsonStringEnumConverter() },
+    };
+
+    private const string FileName = "settings.json";
+
+    // Sliders change their values continuously, so writing to disk
+    // is postponed until there is a pause in the changes
+    private static readonly TimeSpan SaveDelay = TimeSpan.FromMilliseconds(500);
+
+    private readonly string _filePath;
+    private readonly string _inheritedFilePath;
+    private readonly MessageTimer _saveTimer;
+
+    private AppSettings? _settings;
+    private bool _isTrackingChanges;
+
+    public SettingsService()
+        : this(
+            Path.Combine(GetSettingsFolder(), FileName),
+            Path.Combine(GetSeparateInstallFolder(), FileName),
+            SaveDelay)
+    {
+    }
+
+    /// <summary>
+    /// Sets the storage locations and the save delay explicitly — thereby making it
+    /// possible to check the work with the file without touching the settings of the
+    /// user themselves.
+    /// </summary>
+    internal SettingsService(string filePath, string inheritedFilePath, TimeSpan saveDelay)
+    {
+        _filePath = filePath;
+        _inheritedFilePath = inheritedFilePath;
+
+        _saveTimer = new MessageTimer { Interval = saveDelay };
+        _saveTimer.Tick += OnSaveTimerTick;
+    }
+
+    /// <summary>The file being read. The agent's diagnostics report it.</summary>
+    public string FilePath => _filePath;
+
+    /// <summary>
+    /// Reads the settings from disk or returns the default values.
+    /// </summary>
+    /// <remarks>
+    /// Asking twice hands out the same instance rather than reading again. Everything
+    /// binds to what this returns — the window, the popup, the hook — and a second
+    /// instance would mean one of them editing settings nobody else can see.
+    /// </remarks>
+    public AppSettings Load() => _settings ??= ReadOrInherit();
+
+    private AppSettings ReadOrInherit()
+    {
+        AppSettings? stored = ReadFile(_filePath);
+
+        // There is no file of our own — the application may well have been configured
+        // before the move to a package. Taking the settings from there beats starting
+        // from a blank slate
+        bool inherited = stored is null && _filePath != _inheritedFilePath;
+        if (inherited)
+        {
+            stored = ReadFile(_inheritedFilePath);
+            inherited = stored is not null;
+        }
+
+        _settings = stored ?? CreateDefault();
+
+        // Moved settings are fixed in the new place right away rather than on the
+        // first edit: otherwise the application would read someone else's file every
+        // time until then
+        if (inherited)
+        {
+            Save();
+        }
+
+        return _settings;
+    }
+
+    /// <summary>
+    /// Starts saving every change, after a pause. For the settings window: it is the
+    /// only process allowed to write.
+    /// </summary>
+    /// <remarks>
+    /// Reads the file if that has not happened yet. The settings window asks in exactly
+    /// that order — its container hands out this service first and the settings only
+    /// when something needs them — and a version of this that quietly did nothing
+    /// before the first read left the window saving nothing at all.
+    /// </remarks>
+    public void TrackChanges()
+    {
+        if (_isTrackingChanges)
+        {
+            return;
+        }
+
+        Load().PropertyChanged += OnSettingsChanged;
+        _isTrackingChanges = true;
+    }
+
+    /// <summary>
+    /// Re-reads the file. For the agent, when the settings window says it has written.
+    /// </summary>
+    /// <remarks>
+    /// There is nothing to wait for and nothing to debounce: the window writes the file
+    /// whole and moves it into place in one step, and only then says so. Nobody else
+    /// writes it — the agent does not watch the file, and an edit made behind the
+    /// application's back is not a case it is built for.
+    /// </remarks>
+    public void Reload()
+    {
+        if (_settings is not null && ReadFile(_filePath) is { } fresh)
+        {
+            _settings.CopyFrom(fresh);
+        }
+    }
+
+    /// <summary>
+    /// Writes the settings and tells the agent to pick them up.
+    /// </summary>
+    /// <remarks>
+    /// The file is written beside its destination and moved onto it, which on one
+    /// volume is a single step. That way a reader never meets a half-written file —
+    /// and there is a reader, in another process, watching this very file.
+    /// </remarks>
+    public void Save()
+    {
+        if (_settings is null)
+        {
+            return;
+        }
+
+        _saveTimer.Stop();
+
+        try
+        {
+            Directory.CreateDirectory(Path.GetDirectoryName(_filePath)!);
+
+            string temporary = _filePath + ".tmp";
+            File.WriteAllText(temporary, JsonSerializer.Serialize(_settings, SerializerOptions));
+            File.Move(temporary, _filePath, overwrite: true);
+        }
+        catch (Exception e) when (e is IOException or UnauthorizedAccessException)
+        {
+            // The settings are not the kind of thing worth bringing the application down for
+            return;
+        }
+
+        SettingsSignal.NotifyAgent();
+    }
+
+    public void Dispose()
+    {
+        _saveTimer.Tick -= OnSaveTimerTick;
+        _saveTimer.Dispose();
+
+        if (_settings is not null && _isTrackingChanges)
+        {
+            _settings.PropertyChanged -= OnSettingsChanged;
+            _isTrackingChanges = false;
+            Save();
+        }
+    }
+
+    /// <summary>
+    /// The folder the application writes its settings to.
+    /// </summary>
+    private static string GetSettingsFolder()
+    {
+        if (!PackageIdentityNative.IsPackaged)
+        {
+            return GetSeparateInstallFolder();
+        }
+
+        // A package has a data folder of its own, which Windows creates and removes
+        // itself. The application name is not appended to it: the folder belongs to it alone anyway
+        return ApplicationData.Current.LocalFolder.Path;
+    }
+
+    /// <summary>
+    /// The settings folder of a separately installed application — the same source
+    /// the package inherits the settings from on the first launch.
+    /// </summary>
+    private static string GetSeparateInstallFolder() => Path.Combine(
+        Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData),
+        "CursorLang");
+
+    private static AppSettings? ReadFile(string path)
+    {
+        try
+        {
+            if (!File.Exists(path))
+            {
+                return null;
+            }
+
+            return JsonSerializer.Deserialize<AppSettings>(File.ReadAllText(path), SerializerOptions);
+        }
+        catch (Exception e) when (e is IOException or UnauthorizedAccessException or JsonException)
+        {
+            return null;
+        }
+    }
+
+    private static AppSettings CreateDefault()
+    {
+        string uiLanguage = System.Globalization.CultureInfo.CurrentUICulture.TwoLetterISOLanguageName;
+        return new AppSettings { Language = uiLanguage == "ru" ? "ru" : "en" };
+    }
+
+    private void OnSettingsChanged(object? sender, PropertyChangedEventArgs e)
+    {
+        _saveTimer.Stop();
+        _saveTimer.Start();
+    }
+
+    private void OnSaveTimerTick(object? sender, EventArgs e) => Save();
+}

CursorLang.Core/Services/SettingsSignal.cs

@@ -0,0 +1,52 @@
+using System.Runtime.InteropServices;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Tells the agent that settings.json has changed.
+/// </summary>
+/// <remarks>
+/// The message carries nothing but the fact. The temptation to send the changed values
+/// along has to be resisted: the file would stop being the only source of truth, and
+/// the two would part company the first time somebody edits it by hand. All this saves
+/// is the wait — the agent watches the file anyway and would notice on its own, just
+/// later and less predictably.
+///
+/// Order is what makes it safe. The settings window writes the file whole, moves it
+/// into place in one step and only then signals, so by the time the agent reads there
+/// is nothing half-written to read.
+///
+/// A registered message rather than <c>WM_APP + n</c>: the identifier is unique across
+/// the system, so it cannot be confused with anything else that finds its way to that
+/// window.
+/// </remarks>
+internal static class SettingsSignal
+{
+    /// <summary>The window class the agent registers for its hidden window.</summary>
+    internal const string AgentWindowClass = "CursorLang.Agent.Window";
+
+    /// <summary>The message both sides agree on.</summary>
+    internal static uint Message { get; } = RegisterWindowMessage("CursorLang.SettingsChanged");
+
+    /// <summary>
+    /// Wakes the agent, if one is running in this session. Silence is a normal
+    /// answer: the settings window is perfectly usable with no agent behind it.
+    /// </summary>
+    internal static void NotifyAgent()
+    {
+        IntPtr agent = FindWindow(AgentWindowClass, null);
+        if (agent != IntPtr.Zero)
+        {
+            PostMessage(agent, Message, IntPtr.Zero, IntPtr.Zero);
+        }
+    }
+
+    [DllImport("user32.dll", CharSet = CharSet.Unicode, EntryPoint = "RegisterWindowMessageW")]
+    private static extern uint RegisterWindowMessage(string lpString);
+
+    [DllImport("user32.dll", CharSet = CharSet.Unicode, EntryPoint = "FindWindowW")]
+    private static extern IntPtr FindWindow(string lpClassName, string? lpWindowName);
+
+    [DllImport("user32.dll", CharSet = CharSet.Unicode, EntryPoint = "PostMessageW")]
+    private static extern bool PostMessage(IntPtr hWnd, uint message, IntPtr wParam, IntPtr lParam);
+}

CursorLang.Core/Services/SingleInstanceGate.cs

@@ -0,0 +1,139 @@
+using CursorLang.Core.Interop;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Lets only one instance of the application run: a second launch does not bring up
+/// a second window but shows the window of the one already running.
+/// </summary>
+/// <remarks>
+/// The kernel object names are left without the Global prefix, that is, they live in
+/// the session namespace. A single instance for the whole machine would make for an
+/// odd picture with fast user switching: the second user would be left without the
+/// application, and showing them the window of the first one is impossible anyway —
+/// windows belong to a session.
+///
+/// Two processes use this now, and each guards its own slot: the agent so that one
+/// background process runs, the settings window so that a second "Settings" from the
+/// tray raises the window already open instead of a second one. Hence the name part.
+/// </remarks>
+public sealed class SingleInstanceGate : IDisposable
+{
+    /// <summary>The agent's slot — one background process per session.</summary>
+    public const string AgentName = ".Agent";
+
+    /// <summary>The settings window's slot — one window per session.</summary>
+    public const string SettingsName = ".Settings";
+
+    private const string MutexName = "CursorLang.SingleInstance";
+    private const string ActivationEventName = "CursorLang.ActivationRequest";
+
+    private readonly string _mutexName;
+    private readonly string _activationEventName;
+
+    private Mutex? _mutex;
+    private EventWaitHandle? _activationRequest;
+    private RegisteredWaitHandle? _activationWait;
+    private bool _isOwner;
+
+    /// <summary>
+    /// Takes a named slot. The name tells the agent's slot from the settings window's,
+    /// and the tests use one of their own: otherwise they would share a slot with the
+    /// running application and get in its way.
+    /// </summary>
+    public SingleInstanceGate(string nameSuffix)
+    {
+        _mutexName = MutexName + nameSuffix;
+        _activationEventName = ActivationEventName + nameSuffix;
+    }
+
+    /// <summary>
+    /// Another launch asks for the window to be shown.
+    /// </summary>
+    /// <remarks>
+    /// Raised on a thread pool thread, wherever the wait happened to be answered. The
+    /// two hosts get back to their own thread differently — one through the dispatcher,
+    /// one by posting to its window — so neither is assumed here.
+    /// </remarks>
+    public event EventHandler? ActivationRequested;
+
+    /// <summary>
+    /// Takes the single-instance slot. When the application is already running, asks
+    /// it to show itself and returns <c>false</c> — the caller is left to exit.
+    /// </summary>
+    public bool TryAcquire() => TryAcquire(showRunningInstance: true);
+
+    /// <summary>
+    /// The same, with a say in what is to happen to the application already running.
+    /// </summary>
+    /// <param name="showRunningInstance">
+    /// Whether the running application is to be brought up. A launch by Windows
+    /// itself passes <c>false</c>: it was not asked for a window, and the
+    /// application already in the tray is answer enough.
+    /// </param>
+    public bool TryAcquire(bool showRunningInstance)
+    {
+        _mutex = new Mutex(initiallyOwned: false, _mutexName);
+
+        try
+        {
+            _isOwner = _mutex.WaitOne(TimeSpan.Zero, exitContext: false);
+        }
+        catch (AbandonedMutexException)
+        {
+            // The previous instance crashed and did not release the mutex.
+            // It has no owner now, which means the slot is free
+            _isOwner = true;
+        }
+
+        // The event is opened by both instances: the first one to wait for a request,
+        // the second one to make it. Which of them creates the object depends on who
+        // came first and does not affect the work
+        _activationRequest = new EventWaitHandle(false, EventResetMode.AutoReset, _activationEventName);
+
+        if (!_isOwner)
+        {
+            if (showRunningInstance)
+            {
+                ForegroundPermissionNative.GrantToAnyProcess();
+                _activationRequest.Set();
+            }
+
+            return false;
+        }
+
+        // The wait is handed over to the thread pool: there is no reason to hold a
+        // thread of our own for it, and the request may never come
+        _activationWait = ThreadPool.RegisterWaitForSingleObject(
+            _activationRequest,
+            OnActivationSignalled,
+            state: null,
+            Timeout.Infinite,
+            executeOnlyOnce: false);
+
+        return true;
+    }
+
+    public void Dispose()
+    {
+        _activationWait?.Unregister(null);
+        _activationWait = null;
+
+        _activationRequest?.Dispose();
+        _activationRequest = null;
+
+        // The mutex is released by the same thread that took it: both happen
+        // on the user interface thread
+        if (_isOwner)
+        {
+            _mutex?.ReleaseMutex();
+            _isOwner = false;
+        }
+
+        _mutex?.Dispose();
+        _mutex = null;
+    }
+
+    private void OnActivationSignalled(object? state, bool timedOut) =>
+        ActivationRequested?.Invoke(this, EventArgs.Empty);
+}

CursorLang.Core/Services/StartupLaunch.cs

@@ -0,0 +1,54 @@
+using System.Runtime.InteropServices;
+using CursorLang.Core.Interop;
+using Windows.ApplicationModel;
+using Windows.ApplicationModel.Activation;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Whether Windows started the application by itself.
+/// </summary>
+/// <remarks>
+/// A launch of its own accord ends up in the tray without a window: the user asked
+/// for the application to be there when they sign in, not for a window to greet them
+/// every morning. A launch by the user is another matter — the window is what they
+/// clicked for.
+///
+/// The two builds tell the launches apart differently. A build in a folder is
+/// started from the registry, and the command written there carries an argument of
+/// its own — see <see cref="RegistryStartup"/>. A package has no say in its command
+/// line, and Windows is asked about the activation instead.
+/// </remarks>
+internal static class StartupLaunch
+{
+    /// <summary>What the registry entry adds to the path of the application.</summary>
+    internal const string Argument = "--startup";
+
+    /// <summary>Whether this launch is the doing of Windows rather than of the user.</summary>
+    internal static bool IsAutomatic(IReadOnlyList<string> arguments) =>
+        HasArgument(arguments) || IsStartupActivation();
+
+    /// <summary>The command line says the launch comes from the startup entry.</summary>
+    internal static bool HasArgument(IReadOnlyList<string> arguments) =>
+        arguments.Any(argument => string.Equals(argument, Argument, StringComparison.OrdinalIgnoreCase));
+
+    private static bool IsStartupActivation()
+    {
+        if (!PackageIdentityNative.IsPackaged)
+        {
+            return false;
+        }
+
+        try
+        {
+            return AppInstance.GetActivatedEventArgs() is { Kind: ActivationKind.StartupTask };
+        }
+        catch (Exception e) when (e is COMException or InvalidOperationException or NotSupportedException)
+        {
+            // Windows has nothing to say about the activation. A window shown when it
+            // was not asked for is a smaller mishap than an application that hides
+            // when the user has just started it
+            return false;
+        }
+    }
+}

CursorLang.Core/Services/StartupService.cs

@@ -0,0 +1,85 @@
+using System.Runtime.InteropServices;
+using CursorLang.Core.Interop;
+using CursorLang.Core.Models;
+using Windows.ApplicationModel;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Startup, arranged by whatever means the current build has.
+/// </summary>
+/// <remarks>
+/// Startup used to be a scheduled task with the highest rights — otherwise an app
+/// that wanted administrator rights would not start from the startup folder. The
+/// app needs no such rights any more, and the two ways left are simpler.
+///
+/// A package declares the task in its manifest, and Windows lists it for the user
+/// next to the rest under Settings — Apps — Startup. Turned off there, it can no
+/// longer be turned back on by the app. Outside a package the same setting is kept
+/// in the registry: see <see cref="RegistryStartup"/>.
+/// </remarks>
+public sealed class StartupService : IStartupService
+{
+    /// <summary>Matches TaskId in the package manifest.</summary>
+    private const string TaskId = "CursorLangStartup";
+
+    private readonly RegistryStartup _registry = new();
+
+    public async Task<StartupState> GetStateAsync()
+    {
+        if (!PackageIdentityNative.IsPackaged)
+        {
+            return _registry.GetState();
+        }
+
+        try
+        {
+            StartupTask task = await StartupTask.GetAsync(TaskId);
+            return Translate(task.State);
+        }
+        catch (Exception e) when (e is COMException or ArgumentException or InvalidOperationException)
+        {
+            // No task by that name in the manifest: that happens to a package put
+            // together by hand. The setting simply will not show
+            return StartupState.Unavailable;
+        }
+    }
+
+    public async Task<StartupState> SetEnabledAsync(bool enabled)
+    {
+        if (!PackageIdentityNative.IsPackaged)
+        {
+            return _registry.SetEnabled(enabled);
+        }
+
+        try
+        {
+            StartupTask task = await StartupTask.GetAsync(TaskId);
+
+            if (!enabled)
+            {
+                task.Disable();
+                return Translate(task.State);
+            }
+
+            // Windows answers with a state rather than with success: once the user
+            // has forbidden startup, the ban stays
+            return Translate(await task.RequestEnableAsync());
+        }
+        catch (Exception e) when (e is COMException or ArgumentException or InvalidOperationException)
+        {
+            return StartupState.Unavailable;
+        }
+    }
+
+    /// <summary>The state of a Windows task in the app's own terms.</summary>
+    internal static StartupState Translate(StartupTaskState state) => state switch
+    {
+        StartupTaskState.Enabled => StartupState.Enabled,
+        StartupTaskState.EnabledByPolicy => StartupState.EnabledByPolicy,
+        StartupTaskState.Disabled => StartupState.Disabled,
+        StartupTaskState.DisabledByUser => StartupState.DisabledByUser,
+        StartupTaskState.DisabledByPolicy => StartupState.DisabledByPolicy,
+        _ => StartupState.Unavailable,
+    };
+}

CursorLang.Core/Services/UpdateOptions.cs

@@ -0,0 +1,37 @@
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Where the application learns about new versions from.
+/// </summary>
+/// <remarks>
+/// These settings belong to the build rather than to the user: the repository is
+/// chosen by whoever releases the application, and these values have no business
+/// being in <c>settings.json</c>. The defaults point at the repository the
+/// application is built from.
+/// </remarks>
+public sealed class UpdateOptions
+{
+    /// <summary>
+    /// The address of the Gitea server. Its API lives on the same host as the
+    /// repository pages, so this is the same address the repository is opened at
+    /// in a browser.
+    /// </summary>
+    public Uri ServiceUri { get; init; } = new("https://git.alrakis.kz/");
+
+    /// <summary>The project: <c>owner/repository</c>.</summary>
+    public string Project { get; init; } = "alrakis/cursor-lang";
+
+    /// <summary>How often the application checks the releases on its own.</summary>
+    public TimeSpan CheckInterval { get; init; } = TimeSpan.FromDays(1);
+
+    /// <summary>
+    /// An access token for a private repository.
+    /// </summary>
+    /// <remarks>
+    /// Taken from an environment variable rather than from a file in the repository:
+    /// a secret that gets into a build gets to everyone who received it as well.
+    /// A public repository needs no token at all.
+    /// </remarks>
+    public string? AccessToken { get; init; } =
+        Environment.GetEnvironmentVariable("CURSORLANG_UPDATE_TOKEN");
+}

CursorLang.Core/Services/UpdateService.cs

@@ -0,0 +1,224 @@
+using System.Diagnostics;
+using System.Net.Http.Headers;
+using System.Reflection;
+using System.Runtime.InteropServices;
+using CursorLang.Core.Interop;
+using CursorLang.Core.Models;
+using Windows.ApplicationModel;
+
+namespace CursorLang.Core.Services;
+
+/// <summary>
+/// Learns about new versions from the repository and hands the downloaded package
+/// over to the installer.
+/// </summary>
+/// <remarks>
+/// The package is installed by the Windows app installer, not by the application on
+/// its own. Through <c>PackageManager</c> the update would go without a single
+/// window, but then the application would have to explain both an untrusted signature
+/// and a policy ban to the user itself — the installer already knows how to do all
+/// that and shows the package publisher before the installation, not after.
+/// </remarks>
+public sealed class UpdateService : IUpdateService, IDisposable
+{
+    /// <summary>The package is large and the network can be slow: the buffer is taken with room to spare.</summary>
+    private const int BufferSize = 81920;
+
+    /// <summary>The version of the running application — it does not change while it runs.</summary>
+    private static readonly Version Current = DetectCurrentVersion();
+
+    private readonly IReleaseFeed _feed;
+    private readonly HttpClient _client;
+    private readonly bool _ownsClient;
+    private readonly string _downloadFolder;
+
+    public UpdateService(UpdateOptions options)
+    {
+        _client = CreateClient();
+        _ownsClient = true;
+        _downloadFolder = Path.Combine(Path.GetTempPath(), "CursorLang");
+        _feed = new GiteaReleaseFeed(_client, options);
+
+        CurrentVersion = Current;
+    }
+
+    /// <summary>
+    /// Takes the releases, the network and the version explicitly: in tests they are
+    /// not provided by Windows.
+    /// </summary>
+    internal UpdateService(IReleaseFeed feed, HttpClient client, Version current, string downloadFolder)
+    {
+        _feed = feed;
+        _client = client;
+        _ownsClient = false;
+        _downloadFolder = downloadFolder;
+
+        CurrentVersion = current;
+    }
+
+    public bool IsSupported { get; } = DetectSupport();
+
+    public Version CurrentVersion { get; }
+
+    public async Task<ReleaseInfo?> CheckAsync(CancellationToken cancellationToken)
+    {
+        ReleaseInfo? release = await _feed.GetLatestAsync(cancellationToken);
+        return release is not null && release.Version > CurrentVersion ? release : null;
+    }
+
+    public async Task<string> DownloadAsync(
+        ReleaseInfo release,
+        IProgress<double>? progress,
+        CancellationToken cancellationToken)
+    {
+        string path = Path.Combine(_downloadFolder, BuildFileName(release));
+        string partial = path + ".part";
+
+        Directory.CreateDirectory(_downloadFolder);
+        RemoveLeftovers(path);
+
+        using var request = new HttpRequestMessage(HttpMethod.Get, release.Package.Url);
+        _feed.Authorize(request);
+
+        using HttpResponseMessage response = await _client.SendAsync(
+            request, HttpCompletionOption.ResponseHeadersRead, cancellationToken);
+        response.EnsureSuccessStatusCode();
+
+        long total = response.Content.Headers.ContentLength ?? release.Package.Size;
+
+        await using (Stream source = await response.Content.ReadAsStreamAsync(cancellationToken))
+        await using (FileStream target = File.Create(partial))
+        {
+            byte[] buffer = new byte[BufferSize];
+            long copied = 0;
+            int reported = -1;
+            int read;
+
+            while ((read = await source.ReadAsync(buffer, cancellationToken)) > 0)
+            {
+                await target.WriteAsync(buffer.AsMemory(0, read), cancellationToken);
+                copied += read;
+
+                if (total <= 0)
+                {
+                    continue;
+                }
+
+                // The progress bar cannot tell fractions of a percent apart, and
+                // redrawing on every chunk read would cost more than the download itself
+                int percent = (int)(copied * 100 / total);
+                if (percent != reported)
+                {
+                    reported = percent;
+                    progress?.Report(percent / 100d);
+                }
+            }
+        }
+
+        // A file becomes ready only once downloaded in full: an interrupted download
+        // must not stay on disk under the package name
+        File.Move(partial, path, overwrite: true);
+        return path;
+    }
+
+    public void Install(string packagePath) =>
+        Process.Start(new ProcessStartInfo(packagePath) { UseShellExecute = true })?.Dispose();
+
+    public void Dispose()
+    {
+        if (_ownsClient)
+        {
+            _client.Dispose();
+        }
+    }
+
+    private static HttpClient CreateClient()
+    {
+        // The check and the download have different deadlines: seconds are enough for
+        // the first one, while the second one takes minutes on a slow network. So the
+        // client has no shared timeout, and every operation allots time for itself
+        var handler = new SocketsHttpHandler { ConnectTimeout = TimeSpan.FromSeconds(15) };
+        var client = new HttpClient(handler) { Timeout = Timeout.InfiniteTimeSpan };
+
+        // The User-Agent shows who came: a request without one may well be taken
+        // for a robot and rejected by the server
+        client.DefaultRequestHeaders.UserAgent.Add(new ProductInfoHeaderValue("CursorLang", Current.ToString()));
+
+        return client;
+    }
+
+    /// <summary>
+    /// Whether to check for updates at all: a package from the Store gets them from the Store.
+    /// </summary>
+    private static bool DetectSupport()
+    {
+        if (!PackageIdentityNative.IsPackaged)
+        {
+            return true;
+        }
+
+        try
+        {
+            return Package.Current.SignatureKind != PackageSignatureKind.Store;
+        }
+        catch (Exception e) when (e is COMException or InvalidOperationException)
+        {
+            return true;
+        }
+    }
+
+    private static Version DetectCurrentVersion()
+    {
+        if (PackageIdentityNative.IsPackaged)
+        {
+            try
+            {
+                // A package has a version of its own — the one from the manifest. That
+                // is also the one in the release tag, while the assembly version may differ
+                PackageVersion version = Package.Current.Id.Version;
+                return new Version(version.Major, version.Minor, version.Build, version.Revision);
+            }
+            catch (Exception e) when (e is COMException or InvalidOperationException)
+            {
+                // The package was built without a version in the manifest — the assembly version is left
+            }
+        }
+
+        return Assembly.GetEntryAssembly()?.GetName().Version ?? new Version(0, 0, 0, 0);
+    }
+
+    /// <summary>
+    /// The file name on disk. Only the extension is taken from the hosting response:
+    /// the name itself comes from the outside, and a file is created with it.
+    /// </summary>
+    private static string BuildFileName(ReleaseInfo release)
+    {
+        string extension = release.Package.FileName.EndsWith(".msixbundle", StringComparison.OrdinalIgnoreCase)
+            ? ".msixbundle"
+            : ".msix";
+
+        return $"CursorLang-{release.Version}{extension}";
+    }
+
+    /// <summary>
+    /// Removes packages downloaded earlier: they take up a noticeable amount of
+    /// space and are needed only until the installation.
+    /// </summary>
+    private void RemoveLeftovers(string keep)
+    {
+        try
+        {
+            foreach (string file in Directory.EnumerateFiles(_downloadFolder))
+            {
+                if (!string.Equals(file, keep, StringComparison.OrdinalIgnoreCase))
+                {
+                    File.Delete(file);
+                }
+            }
+        }
+        catch (Exception e) when (e is IOException or UnauthorizedAccessException)
+        {
+            // The file is held by another installer — that does not get in the way of the update
+        }
+    }
+}

CursorLang.Core/Threading/MessageLoop.cs

@@ -0,0 +1,94 @@
+using System.Runtime.InteropServices;
+
+namespace CursorLang.Core.Threading;
+
+/// <summary>
+/// The Win32 message loop — what the application has instead of a dispatcher.
+/// </summary>
+/// <remarks>
+/// It lives in Core rather than in the agent because the things that need a pumping
+/// thread do: <see cref="MessageTimer"/> is used by the layout polling and by saving
+/// the settings, and both are Core's. The settings window has a loop of its own, run
+/// by WPF, and everything here works inside it just the same.
+/// </remarks>
+public static class MessageLoop
+{
+    /// <summary>
+    /// Pumps messages until <c>WM_QUIT</c> and returns its exit code.
+    /// </summary>
+    /// <remarks>
+    /// A -1 from GetMessage means the window handle has already gone; going round
+    /// again would spin forever, so the loop gives up instead.
+    /// </remarks>
+    public static int Run()
+    {
+        while (true)
+        {
+            int result = GetMessage(out Message message, IntPtr.Zero, 0, 0);
+            if (result is 0 or -1)
+            {
+                return result == 0 ? (int)message.wParam : 1;
+            }
+
+            TranslateMessage(ref message);
+            DispatchMessage(ref message);
+        }
+    }
+
+    /// <summary>Asks the loop on this thread to finish.</summary>
+    public static void Quit(int exitCode = 0) => PostQuitMessage(exitCode);
+
+    /// <summary>
+    /// Runs everything already waiting in the queue and returns.
+    /// </summary>
+    /// <remarks>
+    /// For the tests and for the rare place that has to let a posted message through
+    /// without giving up control for good.
+    /// </remarks>
+    public static void DrainQueue()
+    {
+        while (PeekMessage(out Message message, IntPtr.Zero, 0, 0, PM_REMOVE))
+        {
+            if (message.message == WM_QUIT)
+            {
+                PostQuitMessage((int)message.wParam);
+                return;
+            }
+
+            TranslateMessage(ref message);
+            DispatchMessage(ref message);
+        }
+    }
+
+    private const uint WM_QUIT = 0x0012;
+    private const uint PM_REMOVE = 0x0001;
+
+    [DllImport("user32.dll", CharSet = CharSet.Unicode, EntryPoint = "GetMessageW")]
+    private static extern int GetMessage(out Message lpMsg, IntPtr hWnd, uint filterMin, uint filterMax);
+
+    [DllImport("user32.dll", CharSet = CharSet.Unicode, EntryPoint = "PeekMessageW")]
+    private static extern bool PeekMessage(
+        out Message lpMsg, IntPtr hWnd, uint filterMin, uint filterMax, uint removeMsg);
+
+    [DllImport("user32.dll")]
+    private static extern bool TranslateMessage(ref Message lpMsg);
+
+    [DllImport("user32.dll", CharSet = CharSet.Unicode, EntryPoint = "DispatchMessageW")]
+    private static extern IntPtr DispatchMessage(ref Message lpMsg);
+
+    [DllImport("user32.dll")]
+    private static extern void PostQuitMessage(int exitCode);
+
+    [StructLayout(LayoutKind.Sequential)]
+    private struct Message
+    {
+        public IntPtr hwnd;
+        public uint message;
+        public IntPtr wParam;
+        public IntPtr lParam;
+        public uint time;
+        public int x;
+        public int y;
+        public uint lPrivate;
+    }
+}

CursorLang.Core/Threading/MessageTimer.cs

@@ -0,0 +1,70 @@
+using System.Runtime.InteropServices;
+
+namespace CursorLang.Core.Threading;
+
+/// <summary>
+/// A timer that ticks on the message loop — the agent's stand-in for
+/// <c>DispatcherTimer</c>.
+/// </summary>
+/// <remarks>
+/// <c>SetTimer</c> with a null window binds the timer to the thread rather than to a
+/// window, and <c>DispatchMessage</c> calls the callback straight from the loop. The
+/// upshot is the same as with a dispatcher timer: the tick arrives on the thread that
+/// owns the hook and the popup, so nothing needs marshalling and nothing races.
+///
+/// The callback lives in a field for the reason a hook procedure does: the only
+/// reference to it is held by Win32, and a collected delegate takes the process down
+/// with it at the first tick.
+/// </remarks>
+internal sealed class MessageTimer : IDisposable
+{
+    /// <summary>Windows will not go below this, and pretending otherwise misleads.</summary>
+    private const uint MinimumIntervalMilliseconds = 10;
+
+    private readonly TimerProc _callback;
+
+    private nuint _id;
+
+    internal MessageTimer() => _callback = OnTimer;
+
+    internal event EventHandler? Tick;
+
+    internal TimeSpan Interval { get; set; } = TimeSpan.FromMilliseconds(100);
+
+    internal bool IsRunning => _id != 0;
+
+    /// <summary>Starts the timer, or restarts it from zero when it is already running.</summary>
+    internal void Start()
+    {
+        Stop();
+
+        var milliseconds = (uint)Math.Clamp(
+            Math.Round(Interval.TotalMilliseconds), MinimumIntervalMilliseconds, int.MaxValue);
+
+        _id = SetTimer(IntPtr.Zero, 0, milliseconds, _callback);
+    }
+
+    internal void Stop()
+    {
+        if (_id == 0)
+        {
+            return;
+        }
+
+        KillTimer(IntPtr.Zero, _id);
+        _id = 0;
+    }
+
+    public void Dispose() => Stop();
+
+    private void OnTimer(IntPtr window, uint message, nuint id, uint time) =>
+        Tick?.Invoke(this, EventArgs.Empty);
+
+    private delegate void TimerProc(IntPtr hWnd, uint message, nuint idEvent, uint time);
+
+    [DllImport("user32.dll", SetLastError = true)]
+    private static extern nuint SetTimer(IntPtr hWnd, nuint nIDEvent, uint uElapse, TimerProc lpTimerFunc);
+
+    [DllImport("user32.dll", SetLastError = true)]
+    private static extern bool KillTimer(IntPtr hWnd, nuint uIDEvent);
+}