# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/how-must-an-instance-prove-model-output-provenance-in-an-agent-mesh-without-centralized-attestation.md
# Remnant Warrant:    https://corpusfetch.com/c/how-must-an-instance-prove-model-output-provenance-in-an-agent-mesh-without-centralized-attestation.warrant.json
# Markdown SHA-256:   8792c6d7c966cf3df111c4e45274b629d982b7cb4ae7cc0de9c280c9a637bad8
# Code AST SHA-256:   f74eea8bf1b25ffa157bd4a2ba9c466134c7f6e6430e770de542509345d33482
# Verified Classes:   ProvenanceVerdict, ModelOutput, ProvenancePolicy, ProvenanceManifest, DecentralizedModelProvenanceGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

from dataclasses import dataclass
from enum import Enum, auto
import hashlib
import json

class ProvenanceVerdict(Enum):
    FULL_PROVENANCE = auto()
    PARTIAL_PROVENANCE = auto()
    UNVERIFIED = auto()
    INDEPENDENTLY_WITNESSED = auto()

@dataclass(frozen=True)
class ModelOutput:
    output_id: str
    claimed_model: str
    model_attestation: str | None
    prompt_commitment: str | None
    generation_witness: str | None

@dataclass(frozen=True)
class ProvenancePolicy:
    require_model_attestation: bool
    require_witness_for_critical: bool
    is_critical: bool

@dataclass(frozen=True)
class ProvenanceManifest:
    verdict: ProvenanceVerdict
    directive: str
    manifest_digest: str

class DecentralizedModelProvenanceGuard:
    @staticmethod
    def _hash(data: str) -> str:
        return hashlib.sha256(data.encode("utf-8")).hexdigest()

    @classmethod
    def evaluate_output(
        cls, output: ModelOutput, policy: ProvenancePolicy
    ) -> ProvenanceManifest:
        
        # Gate 1: Independent witness
        if output.generation_witness:
            digest = cls._hash(json.dumps({
                "output": output.output_id,
                "model": output.claimed_model,
                "witness": output.generation_witness
            }, sort_keys=True))
            return ProvenanceManifest(
                verdict=ProvenanceVerdict.INDEPENDENTLY_WITNESSED,
                directive=f"PROCEED: Output {output.output_id} independently witnessed.",
                manifest_digest=digest
            )

        # Gate 2: Model attestation requirement
        if policy.require_model_attestation and not output.model_attestation:
            return ProvenanceManifest(
                verdict=ProvenanceVerdict.UNVERIFIED,
                directive=f"HALT: Output {output.output_id} lacks model attestation.",
                manifest_digest=cls._hash(f"NO_MODEL:{output.output_id}")
            )

        # Gate 3: Witness requirement for critical
        if policy.require_witness_for_critical and policy.is_critical:
            return ProvenanceManifest(
                verdict=ProvenanceVerdict.PARTIAL_PROVENANCE,
                directive=f"HALT: Critical output {output.output_id} lacks independent witness.",
                manifest_digest=cls._hash(f"NO_WITNESS:{output.output_id}")
            )

        # Gate 4: Full provenance
        digest = cls._hash(json.dumps({
            "output": output.output_id,
            "model": output.claimed_model,
            "model_attestation": output.model_attestation,
            "prompt_commitment": output.prompt_commitment
        }, sort_keys=True))
        
        return ProvenanceManifest(
            verdict=ProvenanceVerdict.FULL_PROVENANCE,
            directive=f"PROCEED: Output {output.output_id} with model and prompt provenance.",
            manifest_digest=digest
        )