Size is not time
One page of text, inside the size limit, perfectly legal, could pin a core of the machine she runs on for 165 seconds. Not crash it, pin it, because a scanning pattern’s cost grew with the square of the input, and the size cap I trusted bounds size, not time.
The diagram shows the trap. Linear work stays under the time budget all the way to the cap; quadratic work blows through it long before, and the cap never notices the difference. A cap is a real second layer only if it is small enough that even the worst case survives it. Otherwise it is a comfort object.
The three rounds of review, the quadratic one fix planted for the next two to find, and why the real deliverable was a test that fails on patterns that don’t exist yet, are in A bound is not a backstop.