I got an error "CS..." (C# Compiler) in runtime

This means that the code in your Code Actions is not valid. You can check whether CodeActions compiled using the Compile button in Edit Code window in the designer.

Code Editor

To register your own types from the assembly, you need to call the following method from the WorkflowRuntime object.

_runtime.RegisterAssemblyForCodeActions(Assembly.GetAssembly(typeof(some type from your assembly)));