Write the rule where you can see it
A stopping rule you hold only in your head is a suggestion. Written on a note beside the screen, it becomes a decision you already made when you were calmer. Competitive players I have interviewed almost all do some version of this.
Review sessions in writing
Because the game exports no log, a two-line note after each session is your only record: what state the board mostly sat in, and whether you kept your stopping rule. Two weeks of those notes will tell you more than any guide.
