george-andra: GET /api/session surfaces continuation_session_id for a hidden pre-compression
snapshot; loadSession follows it so a mobile reload mid-compression recovers to the visible
continuation instead of a hidden snapshot (chat looked 'lost'). Resolved 2 conflicts (1615 behind):
sessions.js merged w/ #2971 re-arm guard; routes.py merged w/ _session_source_is_webui branch.
Co-authored-by: george-andra <george-andra@users.noreply.github.com>