Stored Change
One persisted local change, tagged with the clientSeq it carries. Ported from yorkie-js-sdk doc-store.ts (aaa5cb15/#1354). The sequence is what lets a store drop changes a sync has already acknowledged, and what lets a restore detect a hole rather than replaying a discontinuous run.
A plain class, not a data class — a public api-compat holder whose equality is not part of the contract (api-compat rule).