The tempDir here contains a randomly generated aspect 

           string buildTempPath = Path.Combine(Environment.TempPath, Guid.NewGuid().ToString());
            FileSystemHelpers.EnsureDirectory(buildTempPath);
            exe.EnvironmentVariables[WellKnownEnvironmentVariables.BuildTempPath] = buildTempPath;

Consequently we should never be writing to the same path twice