Use GetExecutablePath to defer venv validation as requested

Co-authored-by: davidfowl <[email protected]>

Author: Copilot

src/Aspire.Hosting.Python/PythonAppResourceBuilderExtensions.cs

@@ -120,7 +120,7 @@ public static IResourceBuilder<PythonAppResource> AddPythonApp(
             : Path.Join(appDirectory, virtualEnvironmentPath));
 
         var instrumentationExecutable = virtualEnvironment.GetExecutable("opentelemetry-instrument");
-        var pythonExecutable = virtualEnvironment.GetExecutable("python") ?? "python";
+        var pythonExecutable = virtualEnvironment.GetExecutablePath("python");
         var appExecutable = instrumentationExecutable ?? pythonExecutable;
 
         var resource = new PythonAppResource(name, appExecutable, appDirectory);

src/Aspire.Hosting.Python/VirtualEnvironment.cs

@@ -55,4 +55,21 @@ public string GetRequiredExecutable(string name)
             $"The executable {name} could not be found in the virtual environment at '{virtualEnvironmentPath}' . " +
             "Make sure the virtual environment is initialized and the executable is installed.");
     }
+
+    /// <summary>
+    /// Gets the expected path for an executable in the virtual environment without validating it exists.
+    /// </summary>
+    /// <param name="name">The name of the executable.</param>
+    /// <returns>The expected path to the executable in the virtual environment.</returns>
+    public string GetExecutablePath(string name)
+    {
+        if (OperatingSystem.IsWindows())
+        {
+            return Path.Join(virtualEnvironmentPath, "Scripts", name + ".exe");
+        }
+        else
+        {
+            return Path.Join(virtualEnvironmentPath, "bin", name);
+        }
+    }
 }

tests/Aspire.Hosting.Python.Tests/AddPythonAppTests.cs

@@ -261,8 +261,11 @@ public async Task AddPythonAppWithoutVirtualEnvironment_FallsBackToSystemPython(
         Assert.Equal("pythonProject", pythonProjectResource.Name);
         Assert.Equal(projectDirectory, pythonProjectResource.WorkingDirectory);
 
-        // When venv doesn't exist, should fall back to system "python"
-        Assert.Equal("python", pythonProjectResource.Command);
+        // When venv doesn't exist, should still use the expected venv path (not validated)
+        var expectedPythonPath = OperatingSystem.IsWindows()
+            ? Path.Join(projectDirectory, ".venv", "Scripts", "python.exe")
+            : Path.Join(projectDirectory, ".venv", "bin", "python");
+        Assert.Equal(expectedPythonPath, pythonProjectResource.Command);
 
         var commandArguments = await ArgumentEvaluator.GetArgumentListAsync(pythonProjectResource, TestServiceProvider.Instance);