Reviewer note: W5 H7 wrote Coach assistant prose plaintext into
recommendation_feedback.recommendation_text. Same prose lives
encrypted in coach_messages — backups captured the leak.
Migration 0042_coach_feedback_message_ref adds nullable coachMessageId
(FK + cascade) and drops recommendation_text. Aggregator joins +
decrypts on read; admin view reads through the same path.
Fixes: Sr-H3 (Wave-6 v1.4.23 senior-dev review)
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>