The session is "just" the raw chat history in it's entirety (human and agent) and can be disseminated as such. This is what enables swapping between models, you simply send the whole context.

Not sure how others do it, but opencode stores sessions in a sqlite db and you can extract them and share them as needed.

https://opencode.ai/docs/cli/#export

Pro-tip: Building your own extremely minimal harness takes about 15m and is both fun and enlightening. Agents are unsurprisingly quite good at it, but ask them to walk you through it step by step.

Sounds like you want an orchestration.

Let's assume handoff happens when one "agent" finishes its work on one task, i.e. "submit a PR".

At that point you want to exit the agent/clear context etc (any context the next actor needs should be in the handoff artifact).

And the orchestrator calls the next agent with the artifact.

Claude can do this with subagents. If you want to get more serious, I'd look at "durable workflows" and check out what the pi people have to say: https://earendil-works.github.io/absurd/ https://earendil-works.github.io/absurd/patterns/pi-ai-agent...

you should also look at dbos https://www.dbos.dev/

And then do a search for these terms on HN and get some idea of their shortcomings vs a 'real' orchestration tool like Airflow or Dagster

I do this all the time in my workflow. Use any harness. Ask it to create a markdown file with the information required for the handoff. Use that downstream. Keep a "repo" of those markdown files. Are you trying to orchestrate or manage this sort of process?

Hermes has /handoff to go from cli or desktop to IM, possibly other ways.