At a high-level Porter probably needs to support Bob.retrieve. Determine what underlying functionality needs to be provided to facilitate this workflow.

For Bob specifically:

• Learning about ursulas in treasure map
• Work Orders / capsule - can Porter do work order execution and attachment of cfrags to capsule without decryption or revealing sensitive information - and return capsule for Bob to do the decryption.
  ...others...?

Delivery here could be in the form of a comprehensive list of areas to be tackled, and a list of potential functions (and required inputs and outputs) that could be exposed by Porter. Extra credit for sequence diagrams 😅 j/k .