Let agents cancel open questions; fix snapshots missing same-size edits

internal/store/inbox.go

@@ -190,6 +190,26 @@ func (s *Store) Respond(ctx context.Context, actor string, resolutions []Resolut
 	})
 }
 
+var ErrNotOpen = errors.New("inbox item is not open")
+
+func (s *Store) WithdrawItem(ctx context.Context, id string) error {
+	return s.write(ctx, func(tx *sql.Tx, emit emitFunc) error {
+		res, err := tx.ExecContext(ctx, `UPDATE inbox_items SET state = ?, resolved_at = ?, snoozed_until = NULL WHERE id = ? AND state = ?`,
+			string(api.Dismissed), now(), id, string(api.Open))
+		if err != nil {
+			return err
+		}
+		n, err := res.RowsAffected()
+		if err != nil {
+			return err
+		}
+		if n == 0 {
+			return ErrNotOpen
+		}
+		return emitItem(ctx, tx, emit, "inbox.updated", id, agentActor)
+	})
+}
+
 func dismissTaskInbox(ctx context.Context, tx *sql.Tx, emit emitFunc, taskID, actor string) error {
 	ids := []string{}
 	rows, err := tx.QueryContext(ctx, `SELECT id FROM inbox_items WHERE task_id = ? AND state = ?`, taskID, string(api.Open))