Replace the six cap-mapping unit tests (exact 5536 px value, floor, Anthropic
path, two None cases, worst-case tile math) with one behavioral test: the cap
derived from the real Codex rejection makes the production shrink pass rewrite
a real 5444x6200 PNG Responses ``input_image`` part to within the 30000-patch
budget. That is the user-visible contract; the exact pixel value is an
implementation detail. Keeps the classifier test as the second invariant.
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