Respect NetCoreSdkRoot property for TaskHostParameters

src/Build/Instance/TaskFactories/AssemblyTaskFactory.cs

@@ -656,20 +656,30 @@ private static TaskHostParameters AddNetHostParamsIfNeeded(
             }
 
             string dotnetHostPath = getProperty(Constants.DotnetHostPathEnvVarName)?.EvaluatedValue;
-            string ridGraphPath = getProperty(Constants.RuntimeIdentifierGraphPath)?.EvaluatedValue;
+            string netCoreSdkRoot = getProperty(Constants.NetCoreSdkRoot)?.EvaluatedValue?.TrimEnd('/', '\\');
 
-            if (string.IsNullOrEmpty(dotnetHostPath) || string.IsNullOrEmpty(ridGraphPath))
+            // The NetCoreSdkRoot property got added with .NET 11, so for earlier SDKs we fall back to the RID graph path
+            if (string.IsNullOrEmpty(netCoreSdkRoot))
             {
-                return currentParams;
+                string ridGraphPath = getProperty(Constants.RuntimeIdentifierGraphPath)?.EvaluatedValue;
+                if (!string.IsNullOrEmpty(ridGraphPath))
+                {
+                    netCoreSdkRoot = Path.GetDirectoryName(ridGraphPath);
+                }
             }
 
-            string msBuildAssemblyPath = Path.GetDirectoryName(ridGraphPath) ?? string.Empty;
+            // Both DOTNET_HOST_PATH and NetCoreSdkRoot are required to launch .NET task host.
+            // If both are not present, return the original parameters.
+            if (string.IsNullOrEmpty(dotnetHostPath) || string.IsNullOrEmpty(netCoreSdkRoot))
+            {
+                return currentParams;
+            }
 
             return new TaskHostParameters(
                 runtime: currentParams.Runtime,
                 architecture: currentParams.Architecture,
                 dotnetHostPath: dotnetHostPath,
-                msBuildAssemblyPath: msBuildAssemblyPath);
+                msBuildAssemblyPath: netCoreSdkRoot);
         }
 
         /// <summary>

src/Build/Resources/Constants.cs

@@ -120,6 +120,11 @@ internal static class Constants
         /// </summary>
         internal const string RuntimeIdentifierGraphPath = nameof(RuntimeIdentifierGraphPath);
 
+        /// <summary>
+        /// The project property name used to get the root of the .NET Core SDK.
+        /// </summary>
+        internal const string NetCoreSdkRoot = nameof(NetCoreSdkRoot);
+
         /// <summary>
         /// Defines the name of dotnet process based on the operating system.
         /// </summary>