Clarify in the diagram that launching DTR using Task and submitting attachments using $submit-attachment are FHIR transactions defined in CDex rather a distinct actor as implied by the diagram. Whether they are performed within a system or passed to the separate 3rd party applications is an implementation specific architectural detail not covered in CDex.  

Also the same holds true for DTR.  I propose show 2 sets of sequence diagrams to illustrate this.  The first is a high level diagram that abstract the the interaction to black box function for getting documents as additional information.  No Task is needed in this case.

The second diagram is a simplified diagram that aligns more closely with CDex and DTR  and shows when PAS Response Bundle is asking for a Questionnaire to be filled out and the options if the DTR is a provider system function or a separate SMART App.