Receives events from the SEPARATE Clerk instance that owns admin-panel access (organizationMembership.* for ADMIN_CLERK_ORG_ID, user.updated, user.deleted). Verified via Svix HMAC over the raw body with ADMIN_CLERK_WEBHOOK_SIGNING_SECRET. Idempotent per svix-id (Redis, own admin-scoped key namespace, 48h TTL). Gated by IS_CLERK_ENABLED + IS_INIT_CLERK_ADMIN_WEBHOOK. Touches UserAdminModels only — never customer users.