"""Trace evidence survival through fixed lists; no search or LLM is executed."""
import json


def diagnose(required, candidates, ranked, context, supported_claims):
    if not required.issubset(set(candidates)):
        return "retrieval"
    if not required.issubset(set(ranked)):
        return "ranking"
    if not required.issubset(set(context)):
        return "context"
    if not supported_claims:
        return "generation"
    return "supported"


def demo():
    required = {"policy-current", "policy-exception"}
    candidates = ["old-policy", "policy-current", "policy-exception"]
    ranked = ["policy-current", "policy-exception", "old-policy"]
    stage = diagnose(required, candidates, ranked, ranked[:1], True)
    fixed = diagnose(required, candidates, ranked, ranked[:2], True)
    assert stage == "context" and fixed == "supported"
    return dict(first_failure=stage, fixed_evidence_check=fixed,
                generation_still_needs_review=True)


if __name__ == "__main__":
    print(json.dumps(demo(), sort_keys=True))