Per RFC Q2: the 'no subject → pending' path becomes unreachable for
event_registration submissions because ApplyBindingsOnFormSubmit
provisions the Person before this listener fires. Path preserved as
failsafe with explicit warning log so misconfigurations and silent
ApplyBindings failures surface mechanically.
Existing test updated to spy on Log facade and assert the warning fires.
Refs: RFC-WS-6.md §3 (Q2)
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>