git diff for mental models

AI writes students' homework now. Grades are fine — understanding is gone, and no tool can tell the difference. MindDiff can: it finds the false belief behind failing code and proves the diagnosis by running an experiment. The student gets a question, never the answer. The instructor gets the whole class's misconceptions on one screen.

Try a diagnosis See the classroomCodex + GPT-5.6 · OpenAI Build Week

probe.pyexecuted

def add_to_cart(item, cart=[]):
    cart.append(item)
    return cart

print(add_to_cart("apple"))
print(add_to_cart("banana"))

−believed: ['apple'] then ['banana']

+observed: ['apple'] then ['apple', 'banana']

confirmed by experimentmutable-default-arg