Add session abandonment documentation for AI Transport

[GregHolmes]

• Explain abandonment scenarios (tab close, device switch, network loss, idle, app background).
• Document presence-based detection with multi-device tracking.
• Cover four agent response strategies:
  • Immediate termination for expensive streaming,
  • Graceful completion for conversational AI,
  • Background continuation for long-running tasks,
  • Cost optimisation with model switching.
• Include re-attachment handling with rewind and history for client catch-up.

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on this repository.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch feature/AIT-195-session-abandonment

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[mschristensen]

Thanks for this Greg, I took a some stuff from this and included it in: #3016
In the end I felt that the scope of the page is broader than just session abandonment as we originally described in the IA, since it is all related to presence and identity and I wanted to not be prescriptive in the feature docs about what to do when a session is abandoned, as it is up to the application (although we can provide opinionated/concrete examples in a guide later, e.g. use push notifications)
I think a lot of this content is more appropriate for a guide (rather than feature docs) as it references a lot of model/agent framework functionality, so we should come back to this source material when we work on those guides.