Modeling fine-grained changes

When the agent proposes changes a user can individually accept or reject (edits, suggestions), model each change as its own row: what it changes, where (anchored), the agent's reason, and a status (pending/accepted/rejected) with a resolution timestamp. This first-class modeling is what lets the UI present granular accept/reject controls and lets the system track resolution. A change is data, not just text inside a document.