- get_by_child raises ValueError for unknown children: None means ONLY
'existing child, no schedule' (present every day), never 'nonexistent
child silently present'
- concurrent-upsert test uses a gated async executor that pauses task A's
first transactional job after the connection lock is held, then
schedules task B so it provably queues on the lock; deterministic,
not timing-dependent
- leak guard's probe exemption narrowed from whole-function spans to the
exact string-literal lines holding the two sanctioned COUNT(*) queries
Joshua King
4ac2bf1050