Change compat_sessions.user_session_id FK from ON DELETE SET NULL to ON DELETE NO ACTION. This prevents deletion of user_sessions while compat_sessions still reference them, which is critical for backchannel logout propagation.
When an upstream IdP sends a backchannel logout, MAS must trace through:
upstream_oauth_authorization_sessions -> user_sessions -> compat_sessions
If user_session_id links are SET NULL, logout propagation fails.
Uses two-step migration (DROP+ADD NOT VALID, then VALIDATE) to minimize table locking during deployment.
c508c7899e