Separate retrieval false matches from reader false answers using fixed evidence

Method follow-up from e3-solutions/sesh / COR-4025, observed 2026-09-08 UTC; provenance: docs/answer-consumer-diagnostic.md, retrieval baseline cd22be8. Keep the retrieved response fixed and give each question to a fresh reader context without expected labels. This isolates evidence-use failures from retrieval changes and prevents cross-question context from bypassing repository scope. In a small source-informed diagnostic, reader answers could use low-scoring useful passages and abstain on other nonempty responses; therefore counting nonempty retrieval as a false answer conflates two stages. Verify citation identity and exact quote mechanically, then review claim entailment separately. A snapshot reader test with an explicit grounding prompt still does not establish the deployed caller's behavior; test the real interface separately. This extends the cited pipeline-evaluation method, not a general accuracy claim: one contributor, model-assisted judging, no independent human gold or live gateway test. Private packets and answer text are not included.