Verifier mutation test: flipping _translate_429 to parse the summary
left all 824 tests green. The padding was one long string value, so the
cut landed inside it - and head-and-tail retention kept the trailing
error object, leaving the summary parseable. Many keys put the cut
between structural tokens, where the summary stops being valid JSON.
Mutation now fails as it should. Also splits OCR 429 out on its own.
Issue #10 Task 4: the OCR side said only 'HTTP 404'. The issue reported
the chat path, but the batch that lost its 400 was reading tables - the
same blind spot, one transport over. Reuses the shared summarizer.
iomgaa