Fix Sixel rendering in Windows local sessions (#41)

## Summary
- Bundle Microsoft's pinned ConPTY runtime with the matching
`OpenConsole.exe` hosts so local Windows sessions preserve Sixel DCS
payloads rather than silently dropping them through the system console
host.
- Default DECSDM to scrolling/cursor-anchored mode and convert Sixel
image geometry from physical pixels to DIPs on scaled displays.
- Deploy the hosts for app publishes and Control NuGet consumers; update
third-party notice and protocol/release docs.

## Validation
- Core advanced-protocol tests: 50 passed.
- Renderer tests: 40 passed.
- Connection contract tests, including the live ConPTY Sixel transport
regression: 49 passed.
- Visually confirmed `Get-XKCD -Show` renders the comic at the correct
size and position.
- Verified a win-x64 non-AOT publish and both RID-less and RID-specific
NuGet-consumer host layouts.

NativeAOT publishing was not verified locally because the required C++
linker workload is unavailable; CI should cover it.

---------

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: mamoreau-devolutions

Directory.Packages.props

@@ -21,5 +21,6 @@
     <PackageVersion Include="xunit.v3" Version="3.2.2" />
     <PackageVersion Include="xunit.runner.visualstudio" Version="3.1.4" />
     <PackageVersion Include="Microsoft.SourceLink.GitHub" Version="8.0.0" />
+    <PackageVersion Include="Microsoft.Windows.Console.ConPTY" Version="1.24.260710001" />
   </ItemGroup>
 </Project>

docs/advanced-vt-protocols.md

@@ -1,12 +1,11 @@
 # Advanced VT protocols
 
 > [!NOTE]
-> The public out-of-process Windows ConPTY may filter DCS payloads before they
-> reach a terminal client on some Windows builds, and APC sequences (kitty
-> graphics) can be affected the same way. The Core parser and renderer
-> support Sixel and kitty graphics when a connection transports those bytes
-> unchanged (for example, remote/Azure transports); local ConPTY support is
-> limited by the installed Windows pseudoconsole implementation.
+> Windows local sessions use the bundled Microsoft ConPTY runtime, including
+> `OpenConsole.exe`, rather than the OS copy that filters Sixel on some Windows
+> builds. With the built-in engine, Sixel producers such as `Get-XKCD -Show`
+> can render inline images. Other transports must likewise preserve graphics
+> payloads; the optional Ghostty engine does not expose image resources.
 
 `Devolutions.Terminal.Core` parses advanced string protocols without depending on Avalonia,
 Skia, Win32, or an image codec. It exposes decoded Sixel pixels and bounded
@@ -36,6 +35,9 @@ terminator split across input chunks. BEL does not terminate DCS. An `ESC`
 followed by anything other than `\` aborts the DCS and starts the new escape
 sequence.
 
+DECSDM defaults to reset (scrolling mode): Sixel images anchor at the cursor
+unless the application explicitly selects display mode with `CSI ? 80 h`.
+
 ## Limits
 
 Limits are public constants on `TerminalImageLimits` and `VtResourceLimits`.

docs/release.md

@@ -12,7 +12,17 @@ Commands are relative to the repository root.
 - WinApp CLI 0.6.0 for MSIX creation and validation
 - A trusted code-signing certificate for distributable MSIX artifacts
 
-Windows local sessions use ConPTY. Linux and macOS local sessions use the
+Windows local sessions use the pinned `Microsoft.Windows.Console.ConPTY` NuGet
+runtime. Ship `conpty.dll` and the architecture-specific `OpenConsole.exe`
+subdirectories together: without its host, ConPTY can fall back to the OS copy
+and silently lose Sixel output. `ConPtyHost.targets` supplies these files for
+RID-less builds, RID-specific publishes, and Control NuGet consumers, including
+the ARM64 host required by x64 processes running under emulation. Because
+`conpty.dll` lands under `runtimes\<rid>\native` for RID-less builds but at the
+output root once a RID is applied, the hosts are emitted in both layouts; a RID
+does not reliably flow to referenced projects, so the placement cannot depend on
+it.
+Linux and macOS local sessions use the
 bundled `forkpty` relay. The Avalonia shell, settings, renderer, and terminal
 engines are shared.
 
@@ -400,9 +410,9 @@ that `Control` needs, or a project that needs direct access to
 
 ## Platform constraints
 
-- Public out-of-process ConPTY can filter or alter DCS/APC payloads on some
-  Windows builds. Sixel works when the selected connection passes DCS bytes
-  through unchanged.
+- The OS-provided ConPTY can filter graphics payloads on some Windows builds.
+  Local sessions use the bundled runtime to preserve Sixel; remote connections
+  must also transport image sequences unchanged.
 - Avalonia 12 exposes the terminal as a readable UIA Document/Value provider,
   but does not provide a public bridge for native UIA TextPattern/TextPattern2
   or LiveSetting events. Managed ranges and visible notification text remain

src/Devolutions.Terminal.Connection/ConPtyConnection.cs

@@ -158,7 +158,7 @@ public void Resize(int columns, int rows)
             if (pseudoConsole is not null && !pseudoConsole.IsInvalid && !pseudoConsole.IsClosed)
             {
                 var size = new Kernel32.Coord { X = (short)validatedColumns, Y = (short)validatedRows };
-                var hr = Kernel32.ResizePseudoConsole(pseudoConsole, size);
+                var hr = ConPty.ResizePseudoConsole(pseudoConsole, size);
                 if (hr != 0)
                 {
                     Marshal.ThrowExceptionForHR(hr);
@@ -225,7 +225,7 @@ private void StartCore(TerminalLaunchOptions options, CancellationToken cancella
                 X = (short)options.Columns,
                 Y = (short)options.Rows,
             };
-            var hr = Kernel32.CreatePseudoConsole(size, inputRead, outputWrite, 0, out var pseudoConsoleValue);
+            var hr = ConPty.CreatePseudoConsole(size, inputRead, outputWrite, 0, out var pseudoConsoleValue);
             if (hr != 0)
             {
                 Marshal.ThrowExceptionForHR(hr);

src/Devolutions.Terminal.Connection/ConPtyHost.targets

@@ -0,0 +1,34 @@
+<Project>
+  <PropertyGroup>
+    <ConPtyHostSourceRoot Condition="'$(ConPtyHostSourceRoot)' == ''">$(MSBuildThisFileDirectory)..\tools\conpty</ConPtyHostSourceRoot>
+  </PropertyGroup>
+  <!-- ConPTY resolves the host for the native OS architecture relative to conpty.dll,
+       and silently falls back to the OS conhost.exe (which strips DCS/sixel) when it is
+       missing. conpty.dll lands under runtimes\<rid>\native for RID-less builds and at the
+       output root for RID/self-contained publishes, so both layouts are populated: a RID
+       does not necessarily flow to this project when a referencing app is published.
+       ARM64 hosts are included for x64/x86 processes running under Windows emulation. -->
+  <Target Name="IncludeConPtyHosts" BeforeTargets="AssignTargetPaths">
+    <ItemGroup>
+      <_ConPtyArch Include="x86;x64;arm64" />
+      <_ConPtyRuntime Include="win-x86;win-x64;win-arm64" Condition="'$(RuntimeIdentifier)' == ''" />
+      <None Include="@(_ConPtyArch->'$(ConPtyHostSourceRoot)\%(Identity)\OpenConsole.exe')"
+            Link="%(_ConPtyArch.Identity)\OpenConsole.exe"
+            CopyToOutputDirectory="PreserveNewest" CopyToPublishDirectory="PreserveNewest" />
+      <None Include="@(_ConPtyRuntime->'$(ConPtyHostSourceRoot)\x86\OpenConsole.exe')"
+            Condition="'%(_ConPtyRuntime.Identity)' == 'win-x86'"
+            Link="runtimes\%(_ConPtyRuntime.Identity)\native\x86\OpenConsole.exe"
+            CopyToOutputDirectory="PreserveNewest" CopyToPublishDirectory="PreserveNewest" />
+      <None Include="@(_ConPtyRuntime->'$(ConPtyHostSourceRoot)\x64\OpenConsole.exe')"
+            Condition="'%(_ConPtyRuntime.Identity)' == 'win-x86' or '%(_ConPtyRuntime.Identity)' == 'win-x64'"
+            Link="runtimes\%(_ConPtyRuntime.Identity)\native\x64\OpenConsole.exe"
+            CopyToOutputDirectory="PreserveNewest" CopyToPublishDirectory="PreserveNewest" />
+      <None Include="@(_ConPtyRuntime->'$(ConPtyHostSourceRoot)\arm64\OpenConsole.exe')"
+            Link="runtimes\%(_ConPtyRuntime.Identity)\native\arm64\OpenConsole.exe"
+            CopyToOutputDirectory="PreserveNewest" CopyToPublishDirectory="PreserveNewest" />
+      <None Include="$(MSBuildThisFileDirectory)THIRD-PARTY-NOTICES-CONPTY.txt"
+            Link="THIRD-PARTY-NOTICES-CONPTY.txt"
+            CopyToOutputDirectory="PreserveNewest" CopyToPublishDirectory="PreserveNewest" />
+    </ItemGroup>
+  </Target>
+</Project>

src/Devolutions.Terminal.Connection/Devolutions.Terminal.Connection.csproj

@@ -7,6 +7,11 @@
     <IsPackable>false</IsPackable>
   </PropertyGroup>
   <ItemGroup>
+    <PackageReference Include="Microsoft.Windows.Console.ConPTY" GeneratePathProperty="true" ExcludeAssets="build" />
     <ProjectReference Include="..\Devolutions.Terminal.Core\Devolutions.Terminal.Core.csproj" />
   </ItemGroup>
+  <PropertyGroup>
+    <ConPtyHostSourceRoot>$(PkgMicrosoft_Windows_Console_ConPTY)\build\native\runtimes</ConPtyHostSourceRoot>
+  </PropertyGroup>
+  <Import Project="ConPtyHost.targets" />
 </Project>

src/Devolutions.Terminal.Connection/Native/ConPty.cs

@@ -0,0 +1,18 @@
+using System.Runtime.InteropServices;
+using System.Runtime.Versioning;
+using Microsoft.Win32.SafeHandles;
+
+namespace Devolutions.Terminal.Connection.Native;
+
+[SupportedOSPlatform("windows")]
+internal static partial class ConPty
+{
+    [LibraryImport("conpty.dll", EntryPoint = "ConptyCreatePseudoConsole")]
+    internal static partial int CreatePseudoConsole(Kernel32.Coord size, SafeFileHandle hInput, SafeFileHandle hOutput, uint dwFlags, out nint phPC);
+
+    [LibraryImport("conpty.dll", EntryPoint = "ConptyResizePseudoConsole")]
+    internal static partial int ResizePseudoConsole(SafePseudoConsoleHandle hPC, Kernel32.Coord size);
+
+    [LibraryImport("conpty.dll", EntryPoint = "ConptyClosePseudoConsole")]
+    internal static partial void ClosePseudoConsole(nint hPC);
+}

src/Devolutions.Terminal.Connection/Native/Kernel32.cs

@@ -68,15 +68,6 @@ internal struct ProcessInformation
         public int dwThreadId;
     }
 
-    [LibraryImport("kernel32.dll", SetLastError = true)]
-    internal static partial int CreatePseudoConsole(Coord size, SafeFileHandle hInput, SafeFileHandle hOutput, uint dwFlags, out nint phPC);
-
-    [LibraryImport("kernel32.dll", SetLastError = true)]
-    internal static partial int ResizePseudoConsole(SafePseudoConsoleHandle hPC, Coord size);
-
-    [LibraryImport("kernel32.dll", SetLastError = true)]
-    internal static partial void ClosePseudoConsole(nint hPC);
-
     [LibraryImport("kernel32.dll", SetLastError = true)]
     [return: MarshalAs(UnmanagedType.Bool)]
     internal static partial bool CreatePipe(out SafeFileHandle hReadPipe, out SafeFileHandle hWritePipe, nint lpPipeAttributes, uint nSize);

src/Devolutions.Terminal.Connection/Native/SafeHandles.cs

@@ -21,7 +21,7 @@ internal SafePseudoConsoleHandle(nint handle)
 
     protected override bool ReleaseHandle()
     {
-        Kernel32.ClosePseudoConsole(handle);
+        ConPty.ClosePseudoConsole(handle);
         return true;
     }
 }

src/Devolutions.Terminal.Connection/THIRD-PARTY-NOTICES-CONPTY.txt

@@ -0,0 +1,24 @@
+Microsoft Windows Console ConPTY
+https://github.com/microsoft/terminal
+
+Copyright (c) Microsoft Corporation. All rights reserved.
+
+MIT License
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED *AS IS*, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.