The bare minimum necessary to get an SP2010 workflow going in VS2017.

SharePointWorkflowStub.cs

using Client.SharePoint.Services;
using Microsoft.SharePoint.Workflow;
using Microsoft.SharePoint.WorkflowActions;
using System.Workflow.ComponentModel;

namespace Client.SharePoint.Workflow {
	public class ReportWorkflow : Activity {
		public WorkflowContext __Context {
			get => ((WorkflowContext)(GetValue(__ContextProperty)));
			set => SetValue(__ContextProperty, value);
		}
		public static DependencyProperty __ContextProperty = DependencyProperty.Register(nameof(__Context), typeof(WorkflowContext), typeof(ReportWorkflow));

		public SPWorkflowActivationProperties __ActivationProperties {
			get => (SPWorkflowActivationProperties)GetValue(__ActivationPropertiesProperty);
			set => SetValue(__ActivationPropertiesProperty, value);
		}
		public static DependencyProperty __ActivationPropertiesProperty = DependencyProperty.Register(nameof(__ActivationProperties), typeof(SPWorkflowActivationProperties), typeof(ReportWorkflow));

		protected override ActivityExecutionStatus Execute(ActivityExecutionContext executionContext) {
			// Here's where you execute your magic.
			var workflowService = new WorkflowService();
			
			// Passing __Context is safe. It causes no compiler issues on the other end.
			workflowService.Run(__Context);

			return ActivityExecutionStatus.Closed;
		}
	}
}