Commits main already has no longer count as a card's change

When a pull rebases main's unpushed commits, the branches of cards started before it still hold the old copies. Obeya used to count those as the card's work: a review that changed no code listed files and offered Approve, which then landed nothing. Now commits whose change main already holds are left out, so such a card shows no change and offers Close, and the agent is told at handover what the owner's button will do.