# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/what-invariants-bind-self-verification-when-the-verification-procedure-cannot-verify-itself.md
# Remnant Warrant:    https://corpusfetch.com/c/what-invariants-bind-self-verification-when-the-verification-procedure-cannot-verify-itself.warrant.json
# Markdown SHA-256:   bcc9d2e8155261270f3b4329345c6ec4d4a69f0d5e5ea4d714a8a69cd9c6ea63
# Code AST SHA-256:   ed2ce7e89ad254a7a9734ee9ec36cff6e645a4f2efe01f80bbe0ad4b24c7aebf
# Verified Classes:   VerificationVerdict, VerificationProcedure, CrossVerification, VerificationPolicy, VerificationManifest, SelfVerificationRegressGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

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

class VerificationVerdict(Enum):
    EXTERNALLY_ANCHORED = auto()
    FOUNDATION_ACKNOWLEDGED = auto()
    REGRESS_UNPRINCIPLED = auto()
    CROSS_VERIFICATION_CORRELATED = auto()

@dataclass(frozen=True)
class VerificationProcedure:
    procedure_id: str
    scope: str
    foundation_assumptions: tuple[str, ...]
    regress_terminated_at: str | None
    termination_basis: str  # "EXTERNAL_ANCHOR" | "ASSUMPTION" | "PRAGMATIC" | "NONE"
    is_externally_validated: bool

@dataclass(frozen=True)
class CrossVerification:
    procedure_ids: tuple[str, ...]
    independence_verified: bool

@dataclass(frozen=True)
class VerificationPolicy:
    require_termination_basis: bool

@dataclass(frozen=True)
class VerificationManifest:
    verdict: VerificationVerdict
    directive: str
    manifest_digest: str

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

    @classmethod
    def evaluate_procedure(
        cls, procedure: VerificationProcedure, cross: CrossVerification | None, policy: VerificationPolicy
    ) -> VerificationManifest:
        
        # Gate 1: Externally validated
        if procedure.is_externally_validated:
            digest = cls._hash(json.dumps({
                "procedure": procedure.procedure_id,
                "anchor": "EXTERNAL"
            }, sort_keys=True))
            return VerificationManifest(
                verdict=VerificationVerdict.EXTERNALLY_ANCHORED,
                directive=f"PROCEED: Procedure {procedure.procedure_id} externally validated.",
                manifest_digest=digest
            )

        # Gate 2: Foundation assumptions documented
        if policy.require_termination_basis and procedure.termination_basis == "NONE":
            return VerificationManifest(
                verdict=VerificationVerdict.REGRESS_UNPRINCIPLED,
                directive=f"HALT: Procedure {procedure.procedure_id} regress unprincipled, foundation assumptions implicit.",
                manifest_digest=cls._hash(f"UNPRINCIPLED:{procedure.procedure_id}")
            )

        # Gate 3: Cross-verification independence
        if cross:
            if not cross.independence_verified:
                return VerificationManifest(
                    verdict=VerificationVerdict.CROSS_VERIFICATION_CORRELATED,
                    directive=f"HALT: Cross-verification procedures share assumptions, not independent.",
                    manifest_digest=cls._hash(f"CORRELATED:{procedure.procedure_id}")
                )

        # Gate 4: Foundation acknowledged
        digest = cls._hash(json.dumps({
            "procedure": procedure.procedure_id,
            "scope": procedure.scope,
            "assumptions": procedure.foundation_assumptions,
            "termination": procedure.termination_basis
        }, sort_keys=True))
        
        return VerificationManifest(
            verdict=VerificationVerdict.FOUNDATION_ACKNOWLEDGED,
            directive=f"PROCEED: Procedure {procedure.procedure_id} with {len(procedure.foundation_assumptions)} foundation assumptions acknowledged.",
            manifest_digest=digest
        )