diff --git a/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/IntegrationTesting/src/Deployers/ApplicationDeployer.cs b/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/IntegrationTesting/src/Deployers/ApplicationDeployer.cs
index 6a96659f406835..7acddd5c5527bc 100644
--- a/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/IntegrationTesting/src/Deployers/ApplicationDeployer.cs
+++ b/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/IntegrationTesting/src/Deployers/ApplicationDeployer.cs
@@ -102,7 +102,7 @@ protected void CleanPublishedOutput()
 
         protected string GetDotNetExeForArchitecture()
         {
-            var executableName = DotnetCommandName;
+            var executableName = GetHostDotNetExecutable();
             // We expect x64 dotnet.exe to be on the path but we have to go searching for the x86 version.
             if (DotNetCommands.IsRunningX86OnX64(DeploymentParameters.RuntimeArchitecture))
             {
@@ -116,17 +116,51 @@ protected string GetDotNetExeForArchitecture()
             return executableName;
         }
 
+        // Mirrors dotnet/arcade's RemoteExecutor host resolution. The runtime libraries Helix harness runs
+        // tests against the testhost via $RUNTIME_PATH/dotnet by absolute path and doesn't add dotnet to PATH
+        // (that is only done for workload tests), so launching the host by the bare command name can fail on
+        // machines without a global dotnet. Use the host running this test, and when that isn't dotnet (for
+        // example an apphost-based testhost) resolve the muxer next to the running shared framework.
+        private static string GetHostDotNetExecutable()
+        {
+            string hostName = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? "dotnet.exe" : "dotnet";
+
+            string hostRunner = Process.GetCurrentProcess().MainModule?.FileName;
+            if (!string.IsNullOrEmpty(hostRunner) && string.Equals(Path.GetFileName(hostRunner), hostName, StringComparison.OrdinalIgnoreCase))
+            {
+                return hostRunner;
+            }
+
+            // The running host isn't dotnet (e.g. an apphost). dotnet is located three directories above the
+            // runtime directory, for example:
+            //   runtime -> <root>/shared/Microsoft.NETCore.App/<version>
+            //   dotnet  -> <root>/dotnet
+            // This also works for a locally built runtime/testhost.
+            var runtimeDirectory = Path.GetDirectoryName(typeof(object).Assembly.Location);
+            if (!string.IsNullOrEmpty(runtimeDirectory))
+            {
+                string dotnetRoot = Path.GetFullPath(Path.Combine(runtimeDirectory, "..", "..", ".."));
+                string muxer = Path.Combine(dotnetRoot, hostName);
+                if (File.Exists(muxer))
+                {
+                    return muxer;
+                }
+            }
+
+            return DotnetCommandName;
+        }
+
         protected void ShutDownIfAnyHostProcess(Process hostProcess)
         {
-            if (hostProcess != null && !hostProcess.HasExited)
+            if (hostProcess is not null && IsRunning(hostProcess))
             {
                 Logger.LogInformation("Attempting to cancel process {0}", hostProcess.Id);
 
                 // Shutdown the host process.
                 hostProcess.KillTree();
-                if (!hostProcess.HasExited)
+                if (IsRunning(hostProcess))
                 {
-                    Logger.LogWarning("Unable to terminate the host process with process Id '{processId}", hostProcess.Id);
+                    Logger.LogWarning("Unable to terminate the host process with process Id '{processId}'", hostProcess.Id);
                 }
                 else
                 {
@@ -139,6 +173,22 @@ protected void ShutDownIfAnyHostProcess(Process hostProcess)
             }
         }
 
+        // Process.HasExited throws InvalidOperationException ("No process is associated with this object")
+        // when the process was never started (and also after the Process has been disposed, which disassociates
+        // it). Treat that as "not running" so shutdown cleanup stays non-throwing rather than masking the
+        // original start failure with a misleading exception.
+        private static bool IsRunning(Process hostProcess)
+        {
+            try
+            {
+                return !hostProcess.HasExited;
+            }
+            catch (InvalidOperationException)
+            {
+                return false;
+            }
+        }
+
         protected void AddEnvironmentVariablesToProcess(ProcessStartInfo startInfo, IDictionary<string, string> environmentVariables)
         {
             var environment = startInfo.Environment;
diff --git a/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/IntegrationTesting/src/Deployers/SelfHostDeployer.cs b/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/IntegrationTesting/src/Deployers/SelfHostDeployer.cs
index b5ef69dee0664d..20770b5df7c453 100644
--- a/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/IntegrationTesting/src/Deployers/SelfHostDeployer.cs
+++ b/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/IntegrationTesting/src/Deployers/SelfHostDeployer.cs
@@ -121,7 +121,8 @@ protected async Task<CancellationToken> StartSelfHostAsync()
 
                 AddEnvironmentVariablesToProcess(startInfo, DeploymentParameters.EnvironmentVariables);
 
-                var started = new TaskCompletionSource<object>();
+                var started = new TaskCompletionSource<object>(TaskCreationOptions.RunContinuationsAsynchronously);
+                var hostExitTokenSource = new CancellationTokenSource();
 
                 HostProcess = new Process() { StartInfo = startInfo };
                 HostProcess.EnableRaisingEvents = true;
@@ -134,7 +135,6 @@ protected async Task<CancellationToken> StartSelfHostAsync()
 
                     OutputReceived?.Invoke(sender, dataArgs);
                 };
-                var hostExitTokenSource = new CancellationTokenSource();
                 HostProcess.Exited += (sender, e) =>
                 {
                     Logger.LogInformation("host process ID {pid} shut down", HostProcess.Id);
@@ -151,7 +151,9 @@ protected async Task<CancellationToken> StartSelfHostAsync()
                 }
                 catch (Exception ex)
                 {
+                    // Surface the real launch failure instead of letting it be masked later during disposal.
                     Logger.LogError("Error occurred while starting the process. Exception: {exception}", ex.ToString());
+                    throw;
                 }
 
                 if (HostProcess.HasExited)