Decouple SidecarTaskHostNode from OutOfProcTaskHostNode

src/Build/BackEnd/Components/Communications/NodeProviderOutOfProcTaskHost.cs

@@ -661,9 +661,6 @@ internal bool CreateNode(TaskHostNodeKey nodeKey, INodePacketFactory factory, IN
 
             HandshakeOptions hostContext = nodeKey.HandshakeOptions;
 
-            // If runtime host path is null it means we don't have MSBuild.dll path resolved and there is no need to include it in the command line arguments.
-            string commandLineArgsPlaceholder = "\"{0}\" /nologo /nodemode:2 /nodereuse:{1} /low:{2} /parentpacketversion:{3} ";
-
             // Generate a unique node ID for communication purposes using atomic increment.
             int communicationNodeId = Interlocked.Increment(ref _nextNodeId);
 
@@ -682,10 +679,14 @@ internal bool CreateNode(TaskHostNodeKey nodeKey, INodePacketFactory factory, IN
 
                 var handshake = new Handshake(hostContext, predefinedToolsDirectory: msbuildAssemblyPath);
 
+                bool nodeReuse = NodeReuseIsEnabled(hostContext);
+                // nodemode:2 = Regular TaskHost (short-lived), nodemode:4 = Sidecar TaskHost (long-lived, with callback support)
+                int nodeMode = nodeReuse ? 4 : 2;
+
                 // There is always one task host per host context so we always create just 1 one task host node here.      
                 nodeContexts = GetNodes(
                     runtimeHostPath,
-                    string.Format(commandLineArgsPlaceholder, Path.Combine(msbuildAssemblyPath, Constants.MSBuildAssemblyName), NodeReuseIsEnabled(hostContext), ComponentHost.BuildParameters.LowPriority, NodePacketTypeExtensions.PacketVersion),
+                    $"\"{Path.Combine(msbuildAssemblyPath, Constants.MSBuildAssemblyName)}\" /nologo /nodemode:{nodeMode} /nodereuse:{nodeReuse} /low:{ComponentHost.BuildParameters.LowPriority} /parentpacketversion:{NodePacketTypeExtensions.PacketVersion} ",
                     communicationNodeId,
                     this,
                     handshake,
@@ -707,9 +708,13 @@ internal bool CreateNode(TaskHostNodeKey nodeKey, INodePacketFactory factory, IN
 
             CommunicationsUtilities.Trace("For a host context of {0}, spawning executable from {1}.", hostContext.ToString(), msbuildLocation ?? Constants.MSBuildExecutableName);
 
+            bool nodeReuseNonNet = NodeReuseIsEnabled(hostContext);
+            // nodemode:2 = Regular TaskHost (short-lived), nodemode:4 = Sidecar TaskHost (long-lived, with callback support)
+            int nodeModeNonNet = nodeReuseNonNet ? 4 : 2;
+
             nodeContexts = GetNodes(
                 msbuildLocation,
-                string.Format(commandLineArgsPlaceholder, string.Empty, NodeReuseIsEnabled(hostContext), ComponentHost.BuildParameters.LowPriority, NodePacketTypeExtensions.PacketVersion),
+                $"/nologo /nodemode:{nodeModeNonNet} /nodereuse:{nodeReuseNonNet} /low:{ComponentHost.BuildParameters.LowPriority} /parentpacketversion:{NodePacketTypeExtensions.PacketVersion} ",
                 communicationNodeId,
                 this,
                 new Handshake(hostContext),

src/MSBuild/MSBuild.csproj

@@ -144,7 +144,9 @@
     <Compile Include="MSBuildClientApp.cs" />
     <Compile Include="NodeEndpointOutOfProcTaskHost.cs" />
     <Compile Include="ProjectSchemaValidationHandler.cs" />
+    <Compile Include="OutOfProcTaskHostNodeBase.cs" />
     <Compile Include="OutOfProcTaskHostNode.cs" />
+    <Compile Include="SidecarTaskHostNode.cs" />
     <Compile Include="OutOfProcTaskAppDomainWrapperBase.cs" />
     <Compile Include="OutOfProcTaskAppDomainWrapper.cs" />
     <Compile Include="PerformanceLogEventListener.cs" />