Add account balance anchors

internal/app/manage.go

@@ -61,6 +61,12 @@ func SaveAccount(d *domain.Dataset, v domain.Account) error {
 	}
 	for i, x := range d.Accounts {
 		if x.ID == v.ID {
+			// A balance belongs to the account identity and currency that the
+			// bank reported. Changing either makes the captured figure stale;
+			// clear it so the next connected sync can capture a matching one.
+			if x.Currency != v.Currency || x.ExternalAccountID != v.ExternalAccountID {
+				v.AnchorBalance, v.AnchorDate = "", ""
+			}
 			d.Accounts[i] = v
 			return nil
 		}