Session history for Pi and Codex (follow-on to relay#596) #602

Follow-on to relay#596, which covers Claude only. Pi: readers and a launch hint (--session-id; test it against an existing id first); 8 of 82 sessions share a folder inside the adapter window, so launched Pi terminals need it. Codex: ask the daemon for name and time; the rollout file is gone for most threads, so only a daemon 'not found' may count as gone, never a missing file. Same interface, discovered records and purge guards as relay#596. Found while working relay#596.