affaan-m/ECC · error · ContractError

rule lacks reference evidence

Error message

rule {rule.get('rule_id')} lacks reference evidence

What it means

Each provenance rule must cite at least one piece of reference evidence. When a rule's 'evidence' key is missing, not a list, or an empty list, this ContractError is raised so every derived rule is traceable to its source media.

Solutions

  1. Add a non-empty 'evidence' list to each rule object in the provenance payload.
  2. Check the rule-generation code path that creates rule dicts and ensure it appends evidence items before validation.
  3. Regenerate provenance with the official Tasteforge producer instead of hand-editing rule entries.
  4. Log the rule_id reported in the error to locate the exact offending rule in the payload.

Example fix

// before
rule = {"rule_id": "r1"}
// after
rule = {"rule_id": "r1", "evidence": [{"reference_sha256": "<64-hex>", "times": [0.0], "source_duration": 10.0}]}
Defensive patterns

Strategy: validation

Validate before calling

missing = [r.get('rule_id') for r in payload.get('rules', [])
          if not isinstance(r.get('evidence'), list) or not r['evidence']]
if missing:
    raise ValueError(f"rules lacking evidence: {missing}")

Type guard

def rule_has_evidence(rule: dict) -> bool:
    ev = rule.get("evidence")
    return isinstance(ev, list) and len(ev) > 0 and all(isinstance(i, dict) for i in ev)

Try / catch

try:
    validate_provenance(payload)
except ContractError as e:
    if "lacks reference evidence" in str(e):
        rule_id = str(e).split()[-1] if e.args else "unknown"
        payload = attach_evidence(payload, rule_id)
    else:
        raise

Prevention

When it happens

Trigger: validate_provenance encounters a rule dict like {'rule_id': 'r1'} with no 'evidence' key, {'rule_id': 'r1', 'evidence': None}, or {'rule_id': 'r1', 'evidence': []}.

Common situations: Producers that build rule objects but never attach evidence entries; a rule template copied without its evidence field; evidence stripped by a downstream transform that drops keys; rules authored manually in a hand-edited provenance file.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

AI-assisted analysis of affaan-m/ECC@8321021c54 (2026-09-16). Data as JSON: /api/errors/1c0ab65ee0d6a360. Report an issue: GitHub.

Appendix: source

Thrown at skills/taste-application/scripts/tasteforge/contract.py:266

                digest = anchor.get("source_ref_sha256")
                expected_duration = reference_durations.get(digest) if isinstance(digest, str) else None
                if expected_duration is None or anchor.get("source_duration") != expected_duration:
                    raise ContractError("anchor evidence source duration is not bound to its receipt reference")
    for event in events:
        placement = event.get("placement")
        if not isinstance(placement, dict) or not {"safe_area", "max_coverage", "occlusion_policy"}.issubset(placement):
            raise ContractError(f"effect {event.get('effect')} lacks placement constraints")


def validate_provenance(payload: dict[str, Any]) -> None:
    """Require every declared rule to cite immutable, timestamped evidence."""
    rules = payload.get("rules")
    if not isinstance(rules, list) or not rules:
        raise ContractError("provenance must contain derived rules")
    for rule in rules:
        evidence = rule.get("evidence")
        if not isinstance(evidence, list) or not evidence:
            raise ContractError(f"rule {rule.get('rule_id')} lacks reference evidence")
        for item in evidence:
            digest = item.get("reference_sha256")
            if not isinstance(digest, str) or len(digest) != 64:
                raise ContractError(f"rule {rule.get('rule_id')} lacks immutable reference evidence")
            times = item.get("times")
            if not isinstance(times, list) or not times:
                raise ContractError(f"rule {rule.get('rule_id')} lacks time evidence")
            source_duration = item.get("source_duration")
            for time in times:
                _validate_media_time(
                    time, source_duration, label=f"rule {rule.get('rule_id')} time evidence"
                )


def validate_manifests(manifests_dir: str | Path) -> None:
    """Require image, video, and 3D-asset dry-run request manifests."""
    manifests_dir = Path(manifests_dir)
    found = {path.stem for path in manifests_dir.glob("*.json")} if manifests_dir.is_dir() else set()

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