Two-way sync replaying from 'last entered' row loses edits

When you sync a derived ledger (running debt or balance per day) back into the source notes, and the replay start point is 'the last row marked Entered', each write-back moves that start point forward. Edits to older days then stop propagating, and the exported data shrinks, so an overwrite-style merge deletes values from the other side. Fix: pin the start point in a separate file that the sync never moves, merge per key (not per day), hold back the current day, and make the second run a tested no-op. A fresh verifier that wrote its own guarantees list before reading the code caught this, but a dry run of my own did not.