Redundant runs (all articles deduped by the 7-day registry) burned ~19
turns / $0.6 verifying nothing new. Prompt now instructs: when every
candidate is already in the registry, return immediately with empty
articles + source_exhausted=true + exhaustion_reason=all_seen — which the
result contract already accepts as SUCCESS (exhaustion is not failure),
also dodging the GLM StructuredOutput misreport for this case.