From 69397a2f102df6967c4ffdeee1e8fd86a741fd62 Mon Sep 17 00:00:00 2001
From: Simon Cropp <simon.cropp@gmail.com>
Date: Sun, 1 Nov 2026 20:45:20 +1100
Subject: [PATCH] Split DiffEngineTray's package from the Windows head

src/DiffEngineTray was both the Windows tray and the DiffEngineTray
package, which names a package for each RID and holds nothing else. Its
build for no RID packed that list, and first built the Linux and Mac
heads for each of their RIDs, so TrayHead.targets had a branch only one
head took (TrayPointer).

The head is now src/DiffEngineTray.Windows, named DiffEngineTray with
DiffEngineTray as its root namespace, as the other two heads are, so its
pictures and forms keep their resource names. src/DiffEngineTray is the
package and nothing else: ToolPackageRuntimeIdentifiers, PackTrayHeads,
and references to the three heads for build order only. The SDK packs a
tool only from an Exe, and builds it though the package holds none of
its output, so it has a Program.cs that ships nowhere. What the package
is called and says about itself is TrayPackage.props, which both import.

The seven packages have the same entries as before. The Linux and macOS
ones are byte for byte the same; the Windows head's dll differs only in
its embedded PDB, which names the moved source files. DiffEngineTray's
nuspec no longer names a Windows Forms framework reference, which came
from the Windows head and meant nothing for a package of no code.
---
 claude.md                                     |   9 +-
 src/DiffEngine.slnx                           |   6 +
 .../IconPixelsTests.cs                        |   2 +-
 .../DiffEngineTray.Core.csproj                |   2 +-
 src/DiffEngineTray.Core/TrayHead.targets      |  69 +-----
 src/DiffEngineTray.Core/TrayPackage.props     |  14 ++
 .../DiffEngineTray.Tests.csproj               |   2 +-
 .../DebugForm.cs                              |   0
 .../DebugFormLauncher.cs                      |   0
 .../DiffEngineTray.Windows.csproj             |  50 ++++
 .../Extensions.cs                             |   0
 .../FilePurger.cs                             |   0
 .../GlobalSuppressions.cs                     |   0
 .../GlobalUsings.cs                           |   0
 .../HotKey/KeyBindingIds.cs                   |   0
 .../HotKey/KeyModifiers.cs                    |   0
 .../HotKey/KeyName.cs                         |   0
 .../HotKey/KeyRegister.cs                     |   0
 .../Images/Images.cs                          |   0
 .../Images/accept.png                         | Bin
 .../Images/acceptAll.png                      | Bin
 .../Images/active.ico                         | Bin
 .../Images/active.png                         | Bin
 .../Images/cogs.png                           | Bin
 .../Images/default.ico                        | Bin
 .../Images/default.png                        | Bin
 .../Images/delete.png                         | Bin
 .../Images/discard.png                        | Bin
 .../Images/exit.png                           | Bin
 .../Images/folder.png                         | Bin
 .../Images/link.png                           | Bin
 .../Images/vs.png                             | Bin
 .../InternalsVisibleTo.cs                     |   0
 .../IssueQuestion.cs                          |   0
 .../LockedFilesForm.cs                        |   0
 .../LockedFilesHandler.cs                     |   0
 .../MenuBuilder.cs                            |   0
 src/DiffEngineTray.Windows/Program.cs         | 230 +++++++++++++++++
 .../Settings/HotKeyControl.Designer.cs        |   0
 .../Settings/HotKeyControl.cs                 |   0
 .../Settings/HotKeyControl.resx               |   0
 .../Settings/OptionsForm.Designer.cs          |   0
 .../Settings/OptionsForm.cs                   |   0
 .../Settings/OptionsForm.resx                 |   0
 .../Settings/OptionsFormLauncher.cs           |   0
 .../Settings/SettingsValidator.cs             |   0
 .../Startup.cs                                |   0
 src/DiffEngineTray/DiffEngineTray.csproj      |  97 +++++---
 src/DiffEngineTray/Program.cs                 | 233 +-----------------
 49 files changed, 381 insertions(+), 333 deletions(-)
 create mode 100644 src/DiffEngineTray.Core/TrayPackage.props
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/DebugForm.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/DebugFormLauncher.cs (100%)
 create mode 100644 src/DiffEngineTray.Windows/DiffEngineTray.Windows.csproj
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Extensions.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/FilePurger.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/GlobalSuppressions.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/GlobalUsings.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/HotKey/KeyBindingIds.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/HotKey/KeyModifiers.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/HotKey/KeyName.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/HotKey/KeyRegister.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Images/Images.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Images/accept.png (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Images/acceptAll.png (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Images/active.ico (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Images/active.png (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Images/cogs.png (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Images/default.ico (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Images/default.png (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Images/delete.png (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Images/discard.png (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Images/exit.png (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Images/folder.png (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Images/link.png (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Images/vs.png (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/InternalsVisibleTo.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/IssueQuestion.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/LockedFilesForm.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/LockedFilesHandler.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/MenuBuilder.cs (100%)
 create mode 100644 src/DiffEngineTray.Windows/Program.cs
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Settings/HotKeyControl.Designer.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Settings/HotKeyControl.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Settings/HotKeyControl.resx (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Settings/OptionsForm.Designer.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Settings/OptionsForm.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Settings/OptionsForm.resx (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Settings/OptionsFormLauncher.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Settings/SettingsValidator.cs (100%)
 rename src/{DiffEngineTray => DiffEngineTray.Windows}/Startup.cs (100%)

diff --git a/claude.md b/claude.md
index 4547d1d43..5d513facb 100644
--- a/claude.md
+++ b/claude.md
@@ -678,7 +678,7 @@ the comment there about not caching "nothing staged" asks for.
   itself) had not. GLFW opens the X11 extension libraries and `libGL` itself at run time, so only
   `libX11` is left of them.
 
-**DiffEngineTray (`src/DiffEngineTray/`):**
+**DiffEngineTray (`src/DiffEngineTray.*`):**
 - Windows Forms tray application that handles pending file diffs, in two projects. `src/DiffEngineTray.Core`
   is everything that is not WinForms - `Tracker`, both inline hosts, `PiperServer`, the settings,
   `DebugReport`, `IssueLauncher`, `ProcessEx` (which reads a process's image and command line
@@ -686,7 +686,8 @@ the comment there about not caching "nothing staged" asks for.
   `DiffToolLauncher` and `FileLockKiller` (the restart manager's, which compiles anywhere and runs
   only on Windows, Unix locks being advisory) - and builds on every platform, so a macOS or
   Linux head can be put on it. Showing a file in a file manager is the viewer's `RevealFile`,
-  which the core links. `src/DiffEngineTray` is the Windows head:
+  which the core links. `src/DiffEngineTray.Windows` is the Windows head, a `WinExe` named
+  `DiffEngineTray` as the other heads are:
   `Program`, the forms, the hot keys (`KeyRegister`, `KeyName`, which parses into WinForms'
   `Keys`), the icons and the Run key. The menu is the core's `TrayMenu`: PlatformHeads'
   `TrayMenuItem`s built from what the tracker holds, an action for each by id, and tips kept beside
@@ -759,7 +760,9 @@ the comment there about not caching "nothing staged" asks for.
   and `dotnet tool install -g DiffEngineTray` fetches `DiffEngineTray.{rid}` beside it, so the
   command did not change. Each RID's package is its head built for that RID, with that RID's viewer
   at `viewer/{rid}` and the documents folder, with that RID's natives only, at `viewer/documents`.
-  The Windows head's build for no RID packs `DiffEngineTray` (`TrayPointer`), and its
+  `DiffEngineTray` is packed by `src/DiffEngineTray`, a project that is that package and nothing
+  else: a head's build for no RID packs nothing. The SDK packs a tool only from an `Exe`, and builds
+  it though the package holds none of its output, so it has a `Program.cs` that ships nowhere. Its
   `PackTrayHeads` first builds each RID's head by the MSBuild task with `RuntimeIdentifier` added
   and nothing else, as the SDK does for a tool's own RID list: their references are then the
   instances the solution already built, restore is the solution's (`RuntimeIdentifiers` is each
diff --git a/src/DiffEngine.slnx b/src/DiffEngine.slnx
index de4374c34..8df486453 100644
--- a/src/DiffEngine.slnx
+++ b/src/DiffEngine.slnx
@@ -80,10 +80,16 @@
     <BuildType Solution="Release-NotWindows|*" Project="Release" />
     <Build Solution="Release-NotWindows|*" Project="false" />
   </Project>
+  <!-- The package naming every RID's, which packs the Windows head's RIDs, so Windows only too. -->
   <Project Path="DiffEngineTray/DiffEngineTray.csproj">
     <BuildType Solution="Release-NotWindows|*" Project="Release" />
     <Build Solution="Release-NotWindows|*" Project="false" />
   </Project>
+  <!-- The Windows head. -->
+  <Project Path="DiffEngineTray.Windows/DiffEngineTray.Windows.csproj">
+    <BuildType Solution="Release-NotWindows|*" Project="Release" />
+    <Build Solution="Release-NotWindows|*" Project="false" />
+  </Project>
   <!-- Builds everywhere: the tray's non-WinForms half, which a macOS or Linux head shares. -->
   <Project Path="DiffEngineTray.Core/DiffEngineTray.Core.csproj">
     <BuildType Solution="Release-NotWindows|*" Project="Release" />
diff --git a/src/DiffEngineTray.Core.Tests/IconPixelsTests.cs b/src/DiffEngineTray.Core.Tests/IconPixelsTests.cs
index 60fe8899d..78900e229 100644
--- a/src/DiffEngineTray.Core.Tests/IconPixelsTests.cs
+++ b/src/DiffEngineTray.Core.Tests/IconPixelsTests.cs
@@ -87,5 +87,5 @@ static byte[] Ico(int size, byte[] bgra)
     }
 
     static string Image(string name, [CallerFilePath] string source = "") =>
-        Path.Combine(Path.GetDirectoryName(source)!, "..", "DiffEngineTray", "Images", name);
+        Path.Combine(Path.GetDirectoryName(source)!, "..", "DiffEngineTray.Windows", "Images", name);
 }
diff --git a/src/DiffEngineTray.Core/DiffEngineTray.Core.csproj b/src/DiffEngineTray.Core/DiffEngineTray.Core.csproj
index c8d2d6c79..b92aa05fe 100644
--- a/src/DiffEngineTray.Core/DiffEngineTray.Core.csproj
+++ b/src/DiffEngineTray.Core/DiffEngineTray.Core.csproj
@@ -24,7 +24,7 @@
     <!-- One way of showing a file in a file manager, the viewer's, rather than a second one. -->
     <Compile Include="..\DiffEngineViewer\RevealFile.cs" Link="RevealFile.cs" />
     <!-- The Windows head's pictures, under the names it embeds them by, for the heads with no WinForms. -->
-    <EmbeddedResource Include="..\DiffEngineTray\Images\*.ico;..\DiffEngineTray\Images\*.png"
+    <EmbeddedResource Include="..\DiffEngineTray.Windows\Images\*.ico;..\DiffEngineTray.Windows\Images\*.png"
                       LinkBase="Images"
                       LogicalName="DiffEngineTray.Images.%(Filename)%(Extension)" />
   </ItemGroup>
diff --git a/src/DiffEngineTray.Core/TrayHead.targets b/src/DiffEngineTray.Core/TrayHead.targets
index afe4d1818..58c646d16 100644
--- a/src/DiffEngineTray.Core/TrayHead.targets
+++ b/src/DiffEngineTray.Core/TrayHead.targets
@@ -11,21 +11,19 @@
   viewers and six sets of document natives, at tens of MB each.
 
   A build of a head for one of its RIDs packs that RID's package, with that RID's viewer and
-  documents folder in it. The Windows head's own build, for no RID, packs DiffEngineTray, and
-  builds every RID's head first to pack the rest (TrayPointer, below).
+  documents folder in it. A head's build for no RID packs nothing. DiffEngineTray itself is the
+  project in src/DiffEngineTray, which builds every RID's head first to pack the rest.
   -->
 
+  <Import Project="TrayPackage.props" />
+
   <PropertyGroup>
-    <PackAsTool>true</PackAsTool>
-    <PackageId>DiffEngineTray</PackageId>
-    <ToolCommandName>DiffEngineTray</ToolCommandName>
-    <Description>A utility that runs in the notification area, or the menu bar on macOS, and handles the results of file differences.</Description>
     <!--
     So the solution's restore covers each RID's build, since nothing restores for it on its own: it
-    is built by the MSBuild task in PackTrayHeads, which does not restore.
+    is built by the MSBuild task in DiffEngineTray's PackTrayHeads, which does not restore.
     -->
     <RuntimeIdentifiers>$(TrayRids)</RuntimeIdentifiers>
-    <!-- For no RID, so the SDK does not pack the Windows head for every RID itself. -->
+    <!-- For no RID, so the SDK does not pack a head for every RID itself. -->
     <CreateRidSpecificToolPackages Condition="'$(RuntimeIdentifier)' == ''">false</CreateRidSpecificToolPackages>
     <CreateRidSpecificToolPackages Condition="'$(RuntimeIdentifier)' != ''">true</CreateRidSpecificToolPackages>
     <!--
@@ -38,7 +36,7 @@
     .cmd opens a console at every login.
     -->
     <UseAppHost Condition="'$(RuntimeIdentifier)' != ''">false</UseAppHost>
-    <IsPackable Condition="'$(RuntimeIdentifier)' == '' And '$(TrayPointer)' != 'true'">false</IsPackable>
+    <IsPackable Condition="'$(RuntimeIdentifier)' == ''">false</IsPackable>
   </PropertyGroup>
 
   <!--
@@ -127,58 +125,5 @@
     </ItemGroup>
   </Target>
 
-  <!--
-  DiffEngineTray itself, which the Windows head packs: a package naming one for each RID, and
-  nothing else, which `dotnet tool install` reads to choose the one to fetch beside it. Each is
-  packed by a build of its head for that RID, from here, before this package is, so DiffEngineTray
-  is never packed without them.
-
-  By the MSBuild task with RuntimeIdentifier and nothing else, so the projects each one references
-  are the instances the solution already built, as the SDK does for a tool with a RID list of its
-  own. A separate `dotnet pack` for each RID would restore them all again under the solution being
-  built. Build rather than Pack, which ProjectDefaults' GeneratePackageOnBuild hooks the pack to:
-  Pack on its own then publishes for the RID without building for it.
-
-  The RIDs here and in ToolPackageRuntimeIdentifiers have to be the same, and
-  PackageTests.ThePointerNamesEveryRidsPackage checks that what it names was packed.
-  -->
-  <PropertyGroup Condition="'$(TrayPointer)' == 'true' And '$(RuntimeIdentifier)' == ''">
-    <ToolPackageRuntimeIdentifiers>win-x64;win-arm64;linux-x64;linux-arm64;osx-x64;osx-arm64</ToolPackageRuntimeIdentifiers>
-    <GenerateNuspecDependsOn>PackTrayHeads;$(GenerateNuspecDependsOn)</GenerateNuspecDependsOn>
-  </PropertyGroup>
-
-  <!--
-  For restore and build order, nothing else, as DiffEngine references the viewer's heads: restore
-  then covers their RIDs when this is built on its own, and each is built for no RID before it is
-  built for one. Every piece of metadata keeps the head's output, natives included, out of this
-  one's.
-  -->
-  <ItemGroup Condition="'$(TrayPointer)' == 'true' And '$(RuntimeIdentifier)' == ''">
-    <ProjectReference Include="$(MSBuildThisFileDirectory)..\DiffEngineTray.Linux\DiffEngineTray.Linux.csproj"
-                      ReferenceOutputAssembly="false"
-                      Private="false"
-                      ExcludeAssets="all" />
-    <ProjectReference Include="$(MSBuildThisFileDirectory)..\DiffEngineTray.Mac\DiffEngineTray.Mac.csproj"
-                      ReferenceOutputAssembly="false"
-                      Private="false"
-                      ExcludeAssets="all" />
-  </ItemGroup>
-
-  <ItemGroup Condition="'$(TrayPointer)' == 'true' And '$(RuntimeIdentifier)' == ''">
-    <_TrayRidPackage Include="$(MSBuildThisFileDirectory)..\DiffEngineTray\DiffEngineTray.csproj" AdditionalProperties="RuntimeIdentifier=win-x64" />
-    <_TrayRidPackage Include="$(MSBuildThisFileDirectory)..\DiffEngineTray\DiffEngineTray.csproj" AdditionalProperties="RuntimeIdentifier=win-arm64" />
-    <_TrayRidPackage Include="$(MSBuildThisFileDirectory)..\DiffEngineTray.Linux\DiffEngineTray.Linux.csproj" AdditionalProperties="RuntimeIdentifier=linux-x64" />
-    <_TrayRidPackage Include="$(MSBuildThisFileDirectory)..\DiffEngineTray.Linux\DiffEngineTray.Linux.csproj" AdditionalProperties="RuntimeIdentifier=linux-arm64" />
-    <_TrayRidPackage Include="$(MSBuildThisFileDirectory)..\DiffEngineTray.Mac\DiffEngineTray.Mac.csproj" AdditionalProperties="RuntimeIdentifier=osx-x64" />
-    <_TrayRidPackage Include="$(MSBuildThisFileDirectory)..\DiffEngineTray.Mac\DiffEngineTray.Mac.csproj" AdditionalProperties="RuntimeIdentifier=osx-arm64" />
-  </ItemGroup>
-
-  <Target Name="PackTrayHeads"
-          Condition="'$(TrayPointer)' == 'true' And '$(RuntimeIdentifier)' == ''">
-    <MSBuild Projects="@(_TrayRidPackage)"
-             Targets="Build"
-             BuildInParallel="true" />
-  </Target>
-
   <Import Project="$(MSBuildThisFileDirectory)..\DiffEngineViewer.Documents\Documents.targets" />
 </Project>
diff --git a/src/DiffEngineTray.Core/TrayPackage.props b/src/DiffEngineTray.Core/TrayPackage.props
new file mode 100644
index 000000000..6a2a60005
--- /dev/null
+++ b/src/DiffEngineTray.Core/TrayPackage.props
@@ -0,0 +1,14 @@
+<Project>
+
+  <!--
+  What DiffEngineTray is called and says about itself, in its own package and in every RID's:
+  imported by TrayHead.targets for the heads and by src/DiffEngineTray for the package that names
+  them.
+  -->
+  <PropertyGroup>
+    <PackAsTool>true</PackAsTool>
+    <PackageId>DiffEngineTray</PackageId>
+    <ToolCommandName>DiffEngineTray</ToolCommandName>
+    <Description>A utility that runs in the notification area, or the menu bar on macOS, and handles the results of file differences.</Description>
+  </PropertyGroup>
+</Project>
diff --git a/src/DiffEngineTray.Tests/DiffEngineTray.Tests.csproj b/src/DiffEngineTray.Tests/DiffEngineTray.Tests.csproj
index b9edb65fe..f6ee91b95 100644
--- a/src/DiffEngineTray.Tests/DiffEngineTray.Tests.csproj
+++ b/src/DiffEngineTray.Tests/DiffEngineTray.Tests.csproj
@@ -23,7 +23,7 @@
     <PackageReference Include="SimpleInfoName" />
     <PackageReference Include="Verify" />
     <PackageReference Include="ProjectDefaults" PrivateAssets="all" />
-    <ProjectReference Include="..\DiffEngineTray\DiffEngineTray.csproj" />
+    <ProjectReference Include="..\DiffEngineTray.Windows\DiffEngineTray.Windows.csproj" />
     <ProjectReference Include="..\DiffEngine\DiffEngine.csproj" />
     <!--
     Aliased. DiffEngineViewer links DiffEngine's Inline and Protocol sources rather than referencing
diff --git a/src/DiffEngineTray/DebugForm.cs b/src/DiffEngineTray.Windows/DebugForm.cs
similarity index 100%
rename from src/DiffEngineTray/DebugForm.cs
rename to src/DiffEngineTray.Windows/DebugForm.cs
diff --git a/src/DiffEngineTray/DebugFormLauncher.cs b/src/DiffEngineTray.Windows/DebugFormLauncher.cs
similarity index 100%
rename from src/DiffEngineTray/DebugFormLauncher.cs
rename to src/DiffEngineTray.Windows/DebugFormLauncher.cs
diff --git a/src/DiffEngineTray.Windows/DiffEngineTray.Windows.csproj b/src/DiffEngineTray.Windows/DiffEngineTray.Windows.csproj
new file mode 100644
index 000000000..9f43665cc
--- /dev/null
+++ b/src/DiffEngineTray.Windows/DiffEngineTray.Windows.csproj
@@ -0,0 +1,50 @@
+<Project Sdk="Microsoft.NET.Sdk.WindowsDesktop">
+
+  <!--
+  The tray on Windows. Named as the other heads are, so the core's InternalsVisibleTo names it, and
+  the pictures and forms keep their resource names.
+  -->
+  <PropertyGroup>
+    <OutputType>WinExe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <AssemblyName>DiffEngineTray</AssemblyName>
+    <RootNamespace>DiffEngineTray</RootNamespace>
+    <UseWindowsForms>true</UseWindowsForms>
+    <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
+    <NoWarn>NETSDK1137;WFAC010;NU5119</NoWarn>
+    <GenerateDocumentationFile>false</GenerateDocumentationFile>
+    <RollForward>LatestMajor</RollForward>
+    <!-- Packed as DiffEngineTray.win-x64 and .win-arm64, by TrayHead.targets. -->
+    <TrayRids>win-x64;win-arm64</TrayRids>
+  </PropertyGroup>
+  <Target Name="RemoveTargetPlatformIdentifier" BeforeTargets="_CheckForInvalidWindowsDesktopTargetingConfiguration">
+    <PropertyGroup>
+      <TargetPlatformIdentifier>Windows</TargetPlatformIdentifier>
+    </PropertyGroup>
+  </Target>
+  <Target Name="RestoreTargetPlatformIdentifier" AfterTargets="_CheckForInvalidWindowsDesktopTargetingConfiguration">
+    <PropertyGroup>
+      <TargetPlatformIdentifier></TargetPlatformIdentifier>
+    </PropertyGroup>
+  </Target>
+
+  <ItemGroup>
+    <None Remove="**\*.ico" />
+    <None Remove="**\*.png" />
+    <Using Include="DiffEngine" />
+    <Using Include="PlatformHeads" />
+    <EmbeddedResource Include="Images\*.ico" />
+    <EmbeddedResource Include="Images\*.png" />
+    <!-- The tray pieces BuildMonitor's tray shares: SessionEndWindow, MenuOnOpening, IssueLink
+         and LinkOpener. -->
+    <PackageReference Include="PlatformHeads.WindowsForms" />
+    <PackageReference Include="Serilog" />
+    <PackageReference Include="Serilog.Sinks.File" />
+    <PackageReference Include="ProjectDefaults" PrivateAssets="all" />
+    <ProjectReference Include="..\DiffEngine\DiffEngine.csproj" />
+    <!-- Everything that is not WinForms, which a head for another platform shares. -->
+    <ProjectReference Include="..\DiffEngineTray.Core\DiffEngineTray.Core.csproj" />
+  </ItemGroup>
+
+  <Import Project="..\DiffEngineTray.Core\TrayHead.targets" />
+</Project>
diff --git a/src/DiffEngineTray/Extensions.cs b/src/DiffEngineTray.Windows/Extensions.cs
similarity index 100%
rename from src/DiffEngineTray/Extensions.cs
rename to src/DiffEngineTray.Windows/Extensions.cs
diff --git a/src/DiffEngineTray/FilePurger.cs b/src/DiffEngineTray.Windows/FilePurger.cs
similarity index 100%
rename from src/DiffEngineTray/FilePurger.cs
rename to src/DiffEngineTray.Windows/FilePurger.cs
diff --git a/src/DiffEngineTray/GlobalSuppressions.cs b/src/DiffEngineTray.Windows/GlobalSuppressions.cs
similarity index 100%
rename from src/DiffEngineTray/GlobalSuppressions.cs
rename to src/DiffEngineTray.Windows/GlobalSuppressions.cs
diff --git a/src/DiffEngineTray/GlobalUsings.cs b/src/DiffEngineTray.Windows/GlobalUsings.cs
similarity index 100%
rename from src/DiffEngineTray/GlobalUsings.cs
rename to src/DiffEngineTray.Windows/GlobalUsings.cs
diff --git a/src/DiffEngineTray/HotKey/KeyBindingIds.cs b/src/DiffEngineTray.Windows/HotKey/KeyBindingIds.cs
similarity index 100%
rename from src/DiffEngineTray/HotKey/KeyBindingIds.cs
rename to src/DiffEngineTray.Windows/HotKey/KeyBindingIds.cs
diff --git a/src/DiffEngineTray/HotKey/KeyModifiers.cs b/src/DiffEngineTray.Windows/HotKey/KeyModifiers.cs
similarity index 100%
rename from src/DiffEngineTray/HotKey/KeyModifiers.cs
rename to src/DiffEngineTray.Windows/HotKey/KeyModifiers.cs
diff --git a/src/DiffEngineTray/HotKey/KeyName.cs b/src/DiffEngineTray.Windows/HotKey/KeyName.cs
similarity index 100%
rename from src/DiffEngineTray/HotKey/KeyName.cs
rename to src/DiffEngineTray.Windows/HotKey/KeyName.cs
diff --git a/src/DiffEngineTray/HotKey/KeyRegister.cs b/src/DiffEngineTray.Windows/HotKey/KeyRegister.cs
similarity index 100%
rename from src/DiffEngineTray/HotKey/KeyRegister.cs
rename to src/DiffEngineTray.Windows/HotKey/KeyRegister.cs
diff --git a/src/DiffEngineTray/Images/Images.cs b/src/DiffEngineTray.Windows/Images/Images.cs
similarity index 100%
rename from src/DiffEngineTray/Images/Images.cs
rename to src/DiffEngineTray.Windows/Images/Images.cs
diff --git a/src/DiffEngineTray/Images/accept.png b/src/DiffEngineTray.Windows/Images/accept.png
similarity index 100%
rename from src/DiffEngineTray/Images/accept.png
rename to src/DiffEngineTray.Windows/Images/accept.png
diff --git a/src/DiffEngineTray/Images/acceptAll.png b/src/DiffEngineTray.Windows/Images/acceptAll.png
similarity index 100%
rename from src/DiffEngineTray/Images/acceptAll.png
rename to src/DiffEngineTray.Windows/Images/acceptAll.png
diff --git a/src/DiffEngineTray/Images/active.ico b/src/DiffEngineTray.Windows/Images/active.ico
similarity index 100%
rename from src/DiffEngineTray/Images/active.ico
rename to src/DiffEngineTray.Windows/Images/active.ico
diff --git a/src/DiffEngineTray/Images/active.png b/src/DiffEngineTray.Windows/Images/active.png
similarity index 100%
rename from src/DiffEngineTray/Images/active.png
rename to src/DiffEngineTray.Windows/Images/active.png
diff --git a/src/DiffEngineTray/Images/cogs.png b/src/DiffEngineTray.Windows/Images/cogs.png
similarity index 100%
rename from src/DiffEngineTray/Images/cogs.png
rename to src/DiffEngineTray.Windows/Images/cogs.png
diff --git a/src/DiffEngineTray/Images/default.ico b/src/DiffEngineTray.Windows/Images/default.ico
similarity index 100%
rename from src/DiffEngineTray/Images/default.ico
rename to src/DiffEngineTray.Windows/Images/default.ico
diff --git a/src/DiffEngineTray/Images/default.png b/src/DiffEngineTray.Windows/Images/default.png
similarity index 100%
rename from src/DiffEngineTray/Images/default.png
rename to src/DiffEngineTray.Windows/Images/default.png
diff --git a/src/DiffEngineTray/Images/delete.png b/src/DiffEngineTray.Windows/Images/delete.png
similarity index 100%
rename from src/DiffEngineTray/Images/delete.png
rename to src/DiffEngineTray.Windows/Images/delete.png
diff --git a/src/DiffEngineTray/Images/discard.png b/src/DiffEngineTray.Windows/Images/discard.png
similarity index 100%
rename from src/DiffEngineTray/Images/discard.png
rename to src/DiffEngineTray.Windows/Images/discard.png
diff --git a/src/DiffEngineTray/Images/exit.png b/src/DiffEngineTray.Windows/Images/exit.png
similarity index 100%
rename from src/DiffEngineTray/Images/exit.png
rename to src/DiffEngineTray.Windows/Images/exit.png
diff --git a/src/DiffEngineTray/Images/folder.png b/src/DiffEngineTray.Windows/Images/folder.png
similarity index 100%
rename from src/DiffEngineTray/Images/folder.png
rename to src/DiffEngineTray.Windows/Images/folder.png
diff --git a/src/DiffEngineTray/Images/link.png b/src/DiffEngineTray.Windows/Images/link.png
similarity index 100%
rename from src/DiffEngineTray/Images/link.png
rename to src/DiffEngineTray.Windows/Images/link.png
diff --git a/src/DiffEngineTray/Images/vs.png b/src/DiffEngineTray.Windows/Images/vs.png
similarity index 100%
rename from src/DiffEngineTray/Images/vs.png
rename to src/DiffEngineTray.Windows/Images/vs.png
diff --git a/src/DiffEngineTray/InternalsVisibleTo.cs b/src/DiffEngineTray.Windows/InternalsVisibleTo.cs
similarity index 100%
rename from src/DiffEngineTray/InternalsVisibleTo.cs
rename to src/DiffEngineTray.Windows/InternalsVisibleTo.cs
diff --git a/src/DiffEngineTray/IssueQuestion.cs b/src/DiffEngineTray.Windows/IssueQuestion.cs
similarity index 100%
rename from src/DiffEngineTray/IssueQuestion.cs
rename to src/DiffEngineTray.Windows/IssueQuestion.cs
diff --git a/src/DiffEngineTray/LockedFilesForm.cs b/src/DiffEngineTray.Windows/LockedFilesForm.cs
similarity index 100%
rename from src/DiffEngineTray/LockedFilesForm.cs
rename to src/DiffEngineTray.Windows/LockedFilesForm.cs
diff --git a/src/DiffEngineTray/LockedFilesHandler.cs b/src/DiffEngineTray.Windows/LockedFilesHandler.cs
similarity index 100%
rename from src/DiffEngineTray/LockedFilesHandler.cs
rename to src/DiffEngineTray.Windows/LockedFilesHandler.cs
diff --git a/src/DiffEngineTray/MenuBuilder.cs b/src/DiffEngineTray.Windows/MenuBuilder.cs
similarity index 100%
rename from src/DiffEngineTray/MenuBuilder.cs
rename to src/DiffEngineTray.Windows/MenuBuilder.cs
diff --git a/src/DiffEngineTray.Windows/Program.cs b/src/DiffEngineTray.Windows/Program.cs
new file mode 100644
index 000000000..92c7068ed
--- /dev/null
+++ b/src/DiffEngineTray.Windows/Program.cs
@@ -0,0 +1,230 @@
+static class Program
+{
+    /// <summary>
+    /// Synchronous, so that the attribute is on the method the runtime starts. For an
+    /// <c>async Task Main</c> that is a method the compiler writes, which carries none, and the
+    /// thread every window here lives on came up MTA: Clipboard.SetText throws ThreadStateException
+    /// there, so "Copy" in the debug view never copied anything.
+    /// <para>
+    /// Blocking on <see cref="Inner"/> is what that compiler written method did as well. Nothing
+    /// in it awaits until <c>Application.Run()</c> has returned, by which time WinForms has taken
+    /// its synchronization context back off this thread, so what follows continues on the pool
+    /// rather than waiting on a loop that is no longer pumping.
+    /// </para>
+    /// </summary>
+    [STAThread]
+    static void Main()
+    {
+        IssueLauncher.Declined = IssueQuestion.Declined;
+        TrayViewerDirectory.Register();
+        Logging.Init();
+        Application.EnableVisualStyles();
+        Application.SetCompatibleTextRenderingDefault(false);
+        Application.SetHighDpiMode(HighDpiMode.SystemAware);
+
+        try
+        {
+            Inner().GetAwaiter().GetResult();
+        }
+        catch (Exception exception)
+        {
+            Log.Logger.Fatal(exception, "Failed at startup");
+            throw;
+        }
+    }
+
+    static async Task Inner()
+    {
+        var tokenSource = new CancelSource();
+        var cancel = tokenSource.Token;
+        using var mutex = new Mutex(true, "DiffEngine", out var createdNew);
+        if (!createdNew)
+        {
+            Log.Information("Mutex already exists. Exiting.");
+            return;
+        }
+
+        try
+        {
+            TrayVersionFile.Write(VersionReader.VersionString);
+        }
+        catch (Exception exception)
+        {
+            // The marker only gates inline snapshot payloads; the tray must still start
+            Log.Error(exception, "Failed to write the tray version marker");
+        }
+
+        // Before the settings file rather than after it, because nothing between here and the
+        // first use of a setting needs one, and until this line the user is looking at an empty
+        // notification area. Still after the mutex, so a second instance exits without ever
+        // showing an icon.
+        // The tips are those of the menus last shown, which the turns below hold, and are asked
+        // for only as a menu is built, by when there are turns to ask
+        TrayTurns? turns = null;
+        using var tray = NotifyIconTray<TrayIcon>.Open(MenuBuilder.Options(_ => turns?.Tooltip(_)), out var trayError) ??
+                         throw new InvalidOperationException($"Could not make the tray icon. {trayError}");
+        // A picture now rather than at the first turn, which waits on everything below
+        tray.Apply(new(TrayIcon.Default, "DiffEngineTray", []));
+
+        void Warn(string message) =>
+            tray.Notify(new("DiffEngineTray", message, Kind: TrayNotificationKind.Warning));
+
+        if (TrayUpdate.Report() is { } report)
+        {
+            // A failure as a warning, as every balloon of this tray's is
+            tray.Notify(report.Kind == TrayNotificationKind.Info ? report : report with {Kind = TrayNotificationKind.Warning});
+        }
+
+        var settings = GetSettings();
+        if (settings == null)
+        {
+            return;
+        }
+
+        LockedFilesPolicy.AlwaysKill = settings.AlwaysKillLockingProcesses;
+
+        // Ownership of the inline queue is decided here, once, by whether the bind succeeds, and
+        // never transfers. Usually the tray wins, because it starts at login. A viewer that was
+        // already running keeps the queue for as long as it lives, and this tray drives it
+        // remotely for the rest of its own life rather than trying to take over mid flight.
+        await using var owned = OwnedInlineHost.TryOwn(Warn);
+        if (owned is null)
+        {
+            Log.Information("A viewer owns the inline queue. Driving it remotely.");
+        }
+
+        var icon = TrayIcon.Default;
+        await using var tracker = new Tracker(
+            active: () => icon = TrayIcon.Active,
+            inactive: () => icon = TrayIcon.Default,
+            lockedFilesResolver: LockedFilesHandler.Resolve,
+            acceptFailed: move => Warn(
+                $"Could not accept '{move.Name}': the file move keeps failing. The move is still pending, so accept can be retried."),
+            inlineFailed: Warn,
+            inline: owned,
+            scanFailing: Warn);
+
+        // Owning the queue means knowing the moment it changes, rather than finding out on the
+        // next two second scan. Wired before serving starts, so the first patch to arrive counts.
+        if (owned is not null)
+        {
+            owned.Changed = tracker.Refresh;
+            owned.TrackedFiles = tracker;
+            owned.Start();
+        }
+
+        // A logoff or a shutdown does not come back through Application.Run(), so nothing the
+        // unwind below performs happens for one
+        using var sessionEnd = new SessionEndWindow(
+            TraySessionEnd.For(owned, TrayVersionFile.Delete),
+            _ => Log.Error(_, "Failed while the session was ending"));
+
+        // Not a using. Anything throwing between here and the await below would dispose a task
+        // that is still running, and Task.Dispose throws for one that has not completed - which
+        // would replace whatever actually went wrong with an InvalidOperationException. A task
+        // needs no disposal anyway; cancelling it is what ends it
+        var listener = PiperServer.TryBind(out var bindError);
+        if (listener is null)
+        {
+            Log.Error(bindError, "Could not listen on port {Port}", PiperClient.Port);
+            Warn($"Could not listen on port {PiperClient.Port}, so moves and deletes from test runs will not reach the tray. {bindError!.Message}");
+        }
+
+        var task = listener is null ? Task.CompletedTask : PiperServer.Serve(listener, tracker, cancel);
+
+        using var keyRegister = new KeyRegister(tray.Handle);
+        ReBindKeys(settings, keyRegister, tracker, Warn);
+
+        turns = new(
+            tray,
+            tracker,
+            new(
+                Exit: Application.Exit,
+                Options: async () => await OptionsFormLauncher.Launch(keyRegister, tracker),
+                DebugView: async () => await DebugFormLauncher.Launch(tracker),
+                Purge: FilePurger.Launch,
+                OpenDiffTool: DiffToolLauncher.Launch),
+            () => icon);
+
+        // The tray's events are raised on this thread as Application.Run pumps it, and what they
+        // chose is done here too, a turn at a time, as the other heads' loops do
+        using var timer = new System.Windows.Forms.Timer
+        {
+            Interval = (int) TrayLoop.Turn.TotalMilliseconds
+        };
+        timer.Tick += (_, _) => turns.Turn();
+        timer.Start();
+
+        try
+        {
+            Application.Run();
+        }
+        finally
+        {
+            TrayVersionFile.Delete();
+        }
+
+        await tokenSource.CancelAsync();
+        await task;
+    }
+
+    internal static void ReBindKeys(Settings settings, KeyRegister keyRegister, Tracker tracker, Action<string>? warn = null)
+    {
+        foreach (var binding in BuildKeyBindings(settings, tracker))
+        {
+            var hotKey = binding.HotKey;
+            if (keyRegister.TryAddBinding(
+                    binding.Id,
+                    hotKey.Shift,
+                    hotKey.Control,
+                    hotKey.Alt,
+                    hotKey.Key,
+                    binding.Action))
+            {
+                continue;
+            }
+
+            // Said out loud, because the alternative is a hot key that quietly does nothing. Only
+            // settings.json can produce a key name the Options form cannot, so only a hand edit
+            // reaches the first half of this
+            warn?.Invoke(
+                $"Could not bind the hot key '{hotKey.Key}'. It is either not a key name, or already registered by another application.");
+        }
+    }
+
+    // Each configured hot key must map to a distinct KeyBindingIds value.
+    // Reusing an id causes KeyRegister.TryAddBinding to unregister and overwrite the earlier binding.
+    internal static IEnumerable<KeyBinding> BuildKeyBindings(Settings settings, Tracker tracker)
+    {
+        if (settings.DiscardAllHotKey is { } discardAll)
+        {
+            yield return new(KeyBindingIds.DiscardAll, discardAll, () => tracker.Clear());
+        }
+
+        if (settings.AcceptAllHotKey is { } acceptAll)
+        {
+            yield return new(KeyBindingIds.AcceptAll, acceptAll, () => tracker.AcceptAll());
+        }
+
+        if (settings.AcceptOpenHotKey is { } acceptOpen)
+        {
+            yield return new(KeyBindingIds.AcceptOpen, acceptOpen, () => tracker.AcceptOpen());
+        }
+    }
+
+    internal record KeyBinding(int Id, HotKey HotKey, Action Action);
+
+    static Settings? GetSettings()
+    {
+        try
+        {
+            return SettingsHelper.Read();
+        }
+        catch (Exception exception)
+        {
+            Log.Fatal(exception, "Cannot start. Failed to read settings: {FilePath}", SettingsHelper.FilePath);
+            IssueLauncher.LaunchForException($"Cannot start. Failed to read settings: {SettingsHelper.FilePath}", exception);
+            return null;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/DiffEngineTray/Settings/HotKeyControl.Designer.cs b/src/DiffEngineTray.Windows/Settings/HotKeyControl.Designer.cs
similarity index 100%
rename from src/DiffEngineTray/Settings/HotKeyControl.Designer.cs
rename to src/DiffEngineTray.Windows/Settings/HotKeyControl.Designer.cs
diff --git a/src/DiffEngineTray/Settings/HotKeyControl.cs b/src/DiffEngineTray.Windows/Settings/HotKeyControl.cs
similarity index 100%
rename from src/DiffEngineTray/Settings/HotKeyControl.cs
rename to src/DiffEngineTray.Windows/Settings/HotKeyControl.cs
diff --git a/src/DiffEngineTray/Settings/HotKeyControl.resx b/src/DiffEngineTray.Windows/Settings/HotKeyControl.resx
similarity index 100%
rename from src/DiffEngineTray/Settings/HotKeyControl.resx
rename to src/DiffEngineTray.Windows/Settings/HotKeyControl.resx
diff --git a/src/DiffEngineTray/Settings/OptionsForm.Designer.cs b/src/DiffEngineTray.Windows/Settings/OptionsForm.Designer.cs
similarity index 100%
rename from src/DiffEngineTray/Settings/OptionsForm.Designer.cs
rename to src/DiffEngineTray.Windows/Settings/OptionsForm.Designer.cs
diff --git a/src/DiffEngineTray/Settings/OptionsForm.cs b/src/DiffEngineTray.Windows/Settings/OptionsForm.cs
similarity index 100%
rename from src/DiffEngineTray/Settings/OptionsForm.cs
rename to src/DiffEngineTray.Windows/Settings/OptionsForm.cs
diff --git a/src/DiffEngineTray/Settings/OptionsForm.resx b/src/DiffEngineTray.Windows/Settings/OptionsForm.resx
similarity index 100%
rename from src/DiffEngineTray/Settings/OptionsForm.resx
rename to src/DiffEngineTray.Windows/Settings/OptionsForm.resx
diff --git a/src/DiffEngineTray/Settings/OptionsFormLauncher.cs b/src/DiffEngineTray.Windows/Settings/OptionsFormLauncher.cs
similarity index 100%
rename from src/DiffEngineTray/Settings/OptionsFormLauncher.cs
rename to src/DiffEngineTray.Windows/Settings/OptionsFormLauncher.cs
diff --git a/src/DiffEngineTray/Settings/SettingsValidator.cs b/src/DiffEngineTray.Windows/Settings/SettingsValidator.cs
similarity index 100%
rename from src/DiffEngineTray/Settings/SettingsValidator.cs
rename to src/DiffEngineTray.Windows/Settings/SettingsValidator.cs
diff --git a/src/DiffEngineTray/Startup.cs b/src/DiffEngineTray.Windows/Startup.cs
similarity index 100%
rename from src/DiffEngineTray/Startup.cs
rename to src/DiffEngineTray.Windows/Startup.cs
diff --git a/src/DiffEngineTray/DiffEngineTray.csproj b/src/DiffEngineTray/DiffEngineTray.csproj
index 9c64ab8f2..3831aa22b 100644
--- a/src/DiffEngineTray/DiffEngineTray.csproj
+++ b/src/DiffEngineTray/DiffEngineTray.csproj
@@ -1,46 +1,73 @@
-<Project Sdk="Microsoft.NET.Sdk.WindowsDesktop">
+<Project Sdk="Microsoft.NET.Sdk">
 
+  <!--
+  DiffEngineTray itself: a package naming one for each RID, and nothing else, which `dotnet tool
+  install` reads to choose the one to fetch beside it. The heads are DiffEngineTray.Windows, .Linux
+  and .Mac, and each RID's package is packed by a build of its head for that RID, from here, before
+  this package is, so DiffEngineTray is never packed without them.
+
+  By the MSBuild task with RuntimeIdentifier and nothing else, so the projects each one references
+  are the instances the solution already built, as the SDK does for a tool with a RID list of its
+  own. A separate `dotnet pack` for each RID would restore them all again under the solution being
+  built. Build rather than Pack, which ProjectDefaults' GeneratePackageOnBuild hooks the pack to:
+  Pack on its own then publishes for the RID without building for it.
+
+  The RIDs here and in ToolPackageRuntimeIdentifiers have to be the same, and
+  PackageTests.ThePointerNamesEveryRidsPackage checks that what it names was packed.
+
+  Windows only, as the Windows head is, since it packs that head's RIDs.
+  -->
   <PropertyGroup>
-    <OutputType>WinExe</OutputType>
+    <!--
+    An Exe, because the SDK packs a tool only from one, and builds it though this package holds none
+    of its output: Program.cs is that, and ships nowhere.
+    -->
+    <OutputType>Exe</OutputType>
     <TargetFramework>net10.0</TargetFramework>
-    <UseWindowsForms>true</UseWindowsForms>
-    <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
-    <NoWarn>NETSDK1137;WFAC010;NU5119</NoWarn>
+    <AssemblyName>DiffEngineTray</AssemblyName>
     <GenerateDocumentationFile>false</GenerateDocumentationFile>
-    <RollForward>LatestMajor</RollForward>
-    <!-- How it is packed is TrayHead.targets'. -->
-    <TrayRids>win-x64;win-arm64</TrayRids>
-    <!-- This head's build for no RID also packs DiffEngineTray, which names every RID's package. -->
-    <TrayPointer>true</TrayPointer>
+    <ToolPackageRuntimeIdentifiers>win-x64;win-arm64;linux-x64;linux-arm64;osx-x64;osx-arm64</ToolPackageRuntimeIdentifiers>
+    <!-- So the SDK does not pack this project for every RID itself. -->
+    <CreateRidSpecificToolPackages>false</CreateRidSpecificToolPackages>
+    <GenerateNuspecDependsOn>PackTrayHeads;$(GenerateNuspecDependsOn)</GenerateNuspecDependsOn>
   </PropertyGroup>
-  <Target Name="RemoveTargetPlatformIdentifier" BeforeTargets="_CheckForInvalidWindowsDesktopTargetingConfiguration">
-    <PropertyGroup>
-      <TargetPlatformIdentifier>Windows</TargetPlatformIdentifier>
-    </PropertyGroup>
-  </Target>
-  <Target Name="RestoreTargetPlatformIdentifier" AfterTargets="_CheckForInvalidWindowsDesktopTargetingConfiguration">
-    <PropertyGroup>
-      <TargetPlatformIdentifier></TargetPlatformIdentifier>
-    </PropertyGroup>
-  </Target>
 
+  <Import Project="..\DiffEngineTray.Core\TrayPackage.props" />
+
+  <!--
+  For restore and build order, nothing else, as DiffEngine references the viewer's heads: restore
+  then covers their RIDs when this is built on its own, and each is built for no RID before it is
+  built for one. Every piece of metadata keeps the heads' output, natives included, out of this
+  one's.
+  -->
   <ItemGroup>
-    <None Remove="**\*.ico" />
-    <None Remove="**\*.png" />
-    <Using Include="DiffEngine" />
-    <Using Include="PlatformHeads" />
-    <EmbeddedResource Include="Images\*.ico" />
-    <EmbeddedResource Include="Images\*.png" />
-    <!-- The tray pieces BuildMonitor's tray shares: SessionEndWindow, MenuOnOpening, IssueLink
-         and LinkOpener. -->
-    <PackageReference Include="PlatformHeads.WindowsForms" />
-    <PackageReference Include="Serilog" />
-    <PackageReference Include="Serilog.Sinks.File" />
+    <ProjectReference Include="..\DiffEngineTray.Windows\DiffEngineTray.Windows.csproj"
+                      ReferenceOutputAssembly="false"
+                      Private="false"
+                      ExcludeAssets="all" />
+    <ProjectReference Include="..\DiffEngineTray.Linux\DiffEngineTray.Linux.csproj"
+                      ReferenceOutputAssembly="false"
+                      Private="false"
+                      ExcludeAssets="all" />
+    <ProjectReference Include="..\DiffEngineTray.Mac\DiffEngineTray.Mac.csproj"
+                      ReferenceOutputAssembly="false"
+                      Private="false"
+                      ExcludeAssets="all" />
     <PackageReference Include="ProjectDefaults" PrivateAssets="all" />
-    <ProjectReference Include="..\DiffEngine\DiffEngine.csproj" />
-    <!-- Everything that is not WinForms, which a head for another platform shares. -->
-    <ProjectReference Include="..\DiffEngineTray.Core\DiffEngineTray.Core.csproj" />
   </ItemGroup>
 
-  <Import Project="..\DiffEngineTray.Core\TrayHead.targets" />
+  <ItemGroup>
+    <_TrayRidPackage Include="..\DiffEngineTray.Windows\DiffEngineTray.Windows.csproj" AdditionalProperties="RuntimeIdentifier=win-x64" />
+    <_TrayRidPackage Include="..\DiffEngineTray.Windows\DiffEngineTray.Windows.csproj" AdditionalProperties="RuntimeIdentifier=win-arm64" />
+    <_TrayRidPackage Include="..\DiffEngineTray.Linux\DiffEngineTray.Linux.csproj" AdditionalProperties="RuntimeIdentifier=linux-x64" />
+    <_TrayRidPackage Include="..\DiffEngineTray.Linux\DiffEngineTray.Linux.csproj" AdditionalProperties="RuntimeIdentifier=linux-arm64" />
+    <_TrayRidPackage Include="..\DiffEngineTray.Mac\DiffEngineTray.Mac.csproj" AdditionalProperties="RuntimeIdentifier=osx-x64" />
+    <_TrayRidPackage Include="..\DiffEngineTray.Mac\DiffEngineTray.Mac.csproj" AdditionalProperties="RuntimeIdentifier=osx-arm64" />
+  </ItemGroup>
+
+  <Target Name="PackTrayHeads">
+    <MSBuild Projects="@(_TrayRidPackage)"
+             Targets="Build"
+             BuildInParallel="true" />
+  </Target>
 </Project>
diff --git a/src/DiffEngineTray/Program.cs b/src/DiffEngineTray/Program.cs
index 92c7068ed..d938a1a19 100644
--- a/src/DiffEngineTray/Program.cs
+++ b/src/DiffEngineTray/Program.cs
@@ -1,230 +1,3 @@
-static class Program
-{
-    /// <summary>
-    /// Synchronous, so that the attribute is on the method the runtime starts. For an
-    /// <c>async Task Main</c> that is a method the compiler writes, which carries none, and the
-    /// thread every window here lives on came up MTA: Clipboard.SetText throws ThreadStateException
-    /// there, so "Copy" in the debug view never copied anything.
-    /// <para>
-    /// Blocking on <see cref="Inner"/> is what that compiler written method did as well. Nothing
-    /// in it awaits until <c>Application.Run()</c> has returned, by which time WinForms has taken
-    /// its synchronization context back off this thread, so what follows continues on the pool
-    /// rather than waiting on a loop that is no longer pumping.
-    /// </para>
-    /// </summary>
-    [STAThread]
-    static void Main()
-    {
-        IssueLauncher.Declined = IssueQuestion.Declined;
-        TrayViewerDirectory.Register();
-        Logging.Init();
-        Application.EnableVisualStyles();
-        Application.SetCompatibleTextRenderingDefault(false);
-        Application.SetHighDpiMode(HighDpiMode.SystemAware);
-
-        try
-        {
-            Inner().GetAwaiter().GetResult();
-        }
-        catch (Exception exception)
-        {
-            Log.Logger.Fatal(exception, "Failed at startup");
-            throw;
-        }
-    }
-
-    static async Task Inner()
-    {
-        var tokenSource = new CancelSource();
-        var cancel = tokenSource.Token;
-        using var mutex = new Mutex(true, "DiffEngine", out var createdNew);
-        if (!createdNew)
-        {
-            Log.Information("Mutex already exists. Exiting.");
-            return;
-        }
-
-        try
-        {
-            TrayVersionFile.Write(VersionReader.VersionString);
-        }
-        catch (Exception exception)
-        {
-            // The marker only gates inline snapshot payloads; the tray must still start
-            Log.Error(exception, "Failed to write the tray version marker");
-        }
-
-        // Before the settings file rather than after it, because nothing between here and the
-        // first use of a setting needs one, and until this line the user is looking at an empty
-        // notification area. Still after the mutex, so a second instance exits without ever
-        // showing an icon.
-        // The tips are those of the menus last shown, which the turns below hold, and are asked
-        // for only as a menu is built, by when there are turns to ask
-        TrayTurns? turns = null;
-        using var tray = NotifyIconTray<TrayIcon>.Open(MenuBuilder.Options(_ => turns?.Tooltip(_)), out var trayError) ??
-                         throw new InvalidOperationException($"Could not make the tray icon. {trayError}");
-        // A picture now rather than at the first turn, which waits on everything below
-        tray.Apply(new(TrayIcon.Default, "DiffEngineTray", []));
-
-        void Warn(string message) =>
-            tray.Notify(new("DiffEngineTray", message, Kind: TrayNotificationKind.Warning));
-
-        if (TrayUpdate.Report() is { } report)
-        {
-            // A failure as a warning, as every balloon of this tray's is
-            tray.Notify(report.Kind == TrayNotificationKind.Info ? report : report with {Kind = TrayNotificationKind.Warning});
-        }
-
-        var settings = GetSettings();
-        if (settings == null)
-        {
-            return;
-        }
-
-        LockedFilesPolicy.AlwaysKill = settings.AlwaysKillLockingProcesses;
-
-        // Ownership of the inline queue is decided here, once, by whether the bind succeeds, and
-        // never transfers. Usually the tray wins, because it starts at login. A viewer that was
-        // already running keeps the queue for as long as it lives, and this tray drives it
-        // remotely for the rest of its own life rather than trying to take over mid flight.
-        await using var owned = OwnedInlineHost.TryOwn(Warn);
-        if (owned is null)
-        {
-            Log.Information("A viewer owns the inline queue. Driving it remotely.");
-        }
-
-        var icon = TrayIcon.Default;
-        await using var tracker = new Tracker(
-            active: () => icon = TrayIcon.Active,
-            inactive: () => icon = TrayIcon.Default,
-            lockedFilesResolver: LockedFilesHandler.Resolve,
-            acceptFailed: move => Warn(
-                $"Could not accept '{move.Name}': the file move keeps failing. The move is still pending, so accept can be retried."),
-            inlineFailed: Warn,
-            inline: owned,
-            scanFailing: Warn);
-
-        // Owning the queue means knowing the moment it changes, rather than finding out on the
-        // next two second scan. Wired before serving starts, so the first patch to arrive counts.
-        if (owned is not null)
-        {
-            owned.Changed = tracker.Refresh;
-            owned.TrackedFiles = tracker;
-            owned.Start();
-        }
-
-        // A logoff or a shutdown does not come back through Application.Run(), so nothing the
-        // unwind below performs happens for one
-        using var sessionEnd = new SessionEndWindow(
-            TraySessionEnd.For(owned, TrayVersionFile.Delete),
-            _ => Log.Error(_, "Failed while the session was ending"));
-
-        // Not a using. Anything throwing between here and the await below would dispose a task
-        // that is still running, and Task.Dispose throws for one that has not completed - which
-        // would replace whatever actually went wrong with an InvalidOperationException. A task
-        // needs no disposal anyway; cancelling it is what ends it
-        var listener = PiperServer.TryBind(out var bindError);
-        if (listener is null)
-        {
-            Log.Error(bindError, "Could not listen on port {Port}", PiperClient.Port);
-            Warn($"Could not listen on port {PiperClient.Port}, so moves and deletes from test runs will not reach the tray. {bindError!.Message}");
-        }
-
-        var task = listener is null ? Task.CompletedTask : PiperServer.Serve(listener, tracker, cancel);
-
-        using var keyRegister = new KeyRegister(tray.Handle);
-        ReBindKeys(settings, keyRegister, tracker, Warn);
-
-        turns = new(
-            tray,
-            tracker,
-            new(
-                Exit: Application.Exit,
-                Options: async () => await OptionsFormLauncher.Launch(keyRegister, tracker),
-                DebugView: async () => await DebugFormLauncher.Launch(tracker),
-                Purge: FilePurger.Launch,
-                OpenDiffTool: DiffToolLauncher.Launch),
-            () => icon);
-
-        // The tray's events are raised on this thread as Application.Run pumps it, and what they
-        // chose is done here too, a turn at a time, as the other heads' loops do
-        using var timer = new System.Windows.Forms.Timer
-        {
-            Interval = (int) TrayLoop.Turn.TotalMilliseconds
-        };
-        timer.Tick += (_, _) => turns.Turn();
-        timer.Start();
-
-        try
-        {
-            Application.Run();
-        }
-        finally
-        {
-            TrayVersionFile.Delete();
-        }
-
-        await tokenSource.CancelAsync();
-        await task;
-    }
-
-    internal static void ReBindKeys(Settings settings, KeyRegister keyRegister, Tracker tracker, Action<string>? warn = null)
-    {
-        foreach (var binding in BuildKeyBindings(settings, tracker))
-        {
-            var hotKey = binding.HotKey;
-            if (keyRegister.TryAddBinding(
-                    binding.Id,
-                    hotKey.Shift,
-                    hotKey.Control,
-                    hotKey.Alt,
-                    hotKey.Key,
-                    binding.Action))
-            {
-                continue;
-            }
-
-            // Said out loud, because the alternative is a hot key that quietly does nothing. Only
-            // settings.json can produce a key name the Options form cannot, so only a hand edit
-            // reaches the first half of this
-            warn?.Invoke(
-                $"Could not bind the hot key '{hotKey.Key}'. It is either not a key name, or already registered by another application.");
-        }
-    }
-
-    // Each configured hot key must map to a distinct KeyBindingIds value.
-    // Reusing an id causes KeyRegister.TryAddBinding to unregister and overwrite the earlier binding.
-    internal static IEnumerable<KeyBinding> BuildKeyBindings(Settings settings, Tracker tracker)
-    {
-        if (settings.DiscardAllHotKey is { } discardAll)
-        {
-            yield return new(KeyBindingIds.DiscardAll, discardAll, () => tracker.Clear());
-        }
-
-        if (settings.AcceptAllHotKey is { } acceptAll)
-        {
-            yield return new(KeyBindingIds.AcceptAll, acceptAll, () => tracker.AcceptAll());
-        }
-
-        if (settings.AcceptOpenHotKey is { } acceptOpen)
-        {
-            yield return new(KeyBindingIds.AcceptOpen, acceptOpen, () => tracker.AcceptOpen());
-        }
-    }
-
-    internal record KeyBinding(int Id, HotKey HotKey, Action Action);
-
-    static Settings? GetSettings()
-    {
-        try
-        {
-            return SettingsHelper.Read();
-        }
-        catch (Exception exception)
-        {
-            Log.Fatal(exception, "Cannot start. Failed to read settings: {FilePath}", SettingsHelper.FilePath);
-            IssueLauncher.LaunchForException($"Cannot start. Failed to read settings: {SettingsHelper.FilePath}", exception);
-            return null;
-        }
-    }
-}
\ No newline at end of file
+// Never run: DiffEngineTray's package holds only the list of RID packages, and the tray is the head
+// one of those installs. See DiffEngineTray.csproj.
+return 1;