feat(router): A Switched Session Resumes With Its Brief, And Every Handoff Says It Moved

[AndrewTKent]

Executive Summary

A handoff to another account relaunched the session idle, with its in-process workflows gone. Nothing picked the work back up unless someone typed into the pane. Now every handoff relaunches with a first message saying the session moved. A session can also leave itself a brief, a one-line prompt plus a model, that its next relaunch runs with. A planned switch while nobody is at the keyboard resumes its work with nothing typed into the terminal.

Developer Summary

• Notice on by default. ACCOUNTS_HANDOFF_NOTICE now defaults to on, and 0 turns it off. The supervisor reads it at each handoff instead of once at start.
• accounts brief <session-id> --prompt "..." [--model M] writes ~/.accounts/handoff-briefs/<id>.json with mode 0600.
• The supervisor uses the brief once, at all three handoff sites: a session wall, a routing or mode change, and a hold. The prompt follows the notice as the relaunch's single positional prompt, and the model replaces the running one.
• Tests: a brief is read once and removed; the brief follows the notice; an end-to-end accounts set switch relaunches on the new account with the brief's prompt and model; the notice defaults to on; accounts brief writes the file the router reads. Each new branch was broken once, and each break failed exactly one test.
• Validation: the CI pytest set passed, 520 tests. One timing test in the statusline-identity group failed once in an earlier full run and passed on the rerun and three times alone. This change doesn't touch it.