ac3f4aed96
The in_channel surface DOES add a seed: _seed_cron_channel_session CREATES the flat (platform, chat_id, None) session and mirrors the brief into it, because mirror_to_session only APPENDS to an existing session and the flat channel row is otherwise absent for a chat_postMessage delivery. Correct the scheduler thread-skip comment and the test class docstring, which still described the earlier 'let the existing mirror seed it' design.