`willUpdate` keys the geometry epoch and render-lifecycle invalidation on
`changed.has('_serverCfg')`. Before #500 every body replacement went through
Lit's accessor and produced that event; the owner wrote its field directly
and the epoch stopped moving on adoption, staging and rollback — the safe
Resize smoke then measured against a stale model (Validate on c360bcc9).
`MutableConfigAdoption` now reports each replaced reference through
`onBodyReplaced`, which the card wires to `requestUpdate(field, previous)`;
echoes and identity-only changes stay silent, exactly as an unchanged
reference never fired the accessor.
Issue: #500
User-Visible: no
claude[bot]
31c2583e46