# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/how-must-an-instance-isolate-tenant-specific-pii-to-satisfy-right-to-be-forgotten-mandates-at-session-teardown.md
# Remnant Warrant:    https://corpusfetch.com/c/how-must-an-instance-isolate-tenant-specific-pii-to-satisfy-right-to-be-forgotten-mandates-at-session-teardown.warrant.json
# Markdown SHA-256:   729262f00503d0aa0222fac818a5cce725dcfe91e5bf4fae7fd547b6b22d9681
# Code AST SHA-256:   63351a680d309f83260f5f07db25b08afa3a3e18e57e140e7c0b0a1c37704430
# Verified Classes:   ComplianceVerdict, SessionPayload, ComplianceContext, ComplianceManifest, PIIIisolationGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

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

class ComplianceVerdict(Enum):
    SAFE_TO_PERSIST = auto()
    PII_LEAK_RISK = auto()
    TENANT_BOUNDARY_VIOLATION = auto()

@dataclass(frozen=True)
class SessionPayload:
    content: str
    detected_pii_types: frozenset[str]
    transformation_applied: str
    destination_tenant: str

@dataclass(frozen=True)
class ComplianceContext:
    origin_tenant: str
    memory_layer_is_shared: bool

@dataclass(frozen=True)
class ComplianceManifest:
    verdict: ComplianceVerdict
    directive: str
    manifest_digest: str

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

    @classmethod
    def evaluate_payload(
        cls, payload: SessionPayload, ctx: ComplianceContext
    ) -> ComplianceManifest:
        
        # Gate 1: Tenant boundary check
        if ctx.memory_layer_is_shared and payload.destination_tenant != ctx.origin_tenant:
            return ComplianceManifest(
                verdict=ComplianceVerdict.TENANT_BOUNDARY_VIOLATION,
                directive=f"HALT: Cannot write to {payload.destination_tenant} from {ctx.origin_tenant}.",
                manifest_digest=cls._hash(f"TENANT:{ctx.origin_tenant}")
            )

        # Gate 2: PII leak check
        if payload.detected_pii_types and payload.transformation_applied in ("NONE", "HASH_ONLY"):
            return ComplianceManifest(
                verdict=ComplianceVerdict.PII_LEAK_RISK,
                directive=f"HALT: PII {payload.detected_pii_types} not fully scrubbed. Use REDACTED or ENCRYPTED.",
                manifest_digest=cls._hash(f"PII_RISK:{','.join(sorted(payload.detected_pii_types))}")
            )

        # Gate 3: Safe
        digest = cls._hash(json.dumps({
            "pii_types": tuple(sorted(payload.detected_pii_types)),
            "transformation": payload.transformation_applied,
            "tenant": payload.destination_tenant
        }, sort_keys=True))
        
        return ComplianceManifest(
            verdict=ComplianceVerdict.SAFE_TO_PERSIST,
            directive="PROCEED: PII is sufficiently isolated.",
            manifest_digest=digest
        )