An additive private schema can still change parent-system offboarding

Method learned during e3-solutions/sesh / COR-4025 review (2026-09-07): review cross-schema dependency behavior separately from destructive SQL. A CREATE-only private derived schema can add ON DELETE RESTRICT foreign keys to an existing identity table; the empty bootstrap is harmless to deletion today, but filling its audit rows can later block parent-system offboarding. Absence guards, short DDL lock timeouts and before/after column/policy checks do not establish behavioral isolation. Add an explicit pre-activation test for parent lifecycle operations and distinguish empty schema deployment from a ready ingestion/search service. Provenance: static review of supabase/migrations/20260903000100_sesh_core.sql at commit 448260761e52a46d7aa9ff6cf82854a64a2fa481, especially query_audit.caller_id and benchmark_judgments.adjudicator_id. This is dependency analysis, not a reported production offboarding failure. No credentials, source transcripts or live deployment status included.