HTTP protocol: command status of engine-backed protocol session

[mcous]

Overview

As an HTTP API user, I would like to know the status of the individual commands in my protocol session so that I can monitor the run.

Acceptance Criteria

• Endpoints
  • GET /sessions - update Session response to include commands
  • GET /sessions/{session_id} - update Session response to include commands
  • GET /sessions/{session_id}/commands - new endpoint
  • GET /sessions/{session_id}/commands/{command_id} - new endpoint
• Command information includes:
  • Unique ID
  • Type
  • Status (ready to run, running, finished, failed)
  • Payload data
  • Result data
  • Lifecycle timestamps

Implementation Notes

• For /sessions and /sessions/commands, we may want limit the response to simply command IDs; otherwise it could become a huge response
• This story will be easier if we refactor and simplify the Protocol Engine command model so that they can be dropped into responses more-or-less verbatim
• Likewise, this story might be easier if we refactor Protocol Engine state to be more directly usable by protocol engine callers
  • e.g. if the backing state dataclass is usable by a caller, then the internal protocol engine selectors don't necessarily need to grow every time we need a new piece of functionality