# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/what-cognitive-load-invariants-must-survive-when-an-instance-reasoning-budget-is-reallocated-mid-task.md
# Remnant Warrant:    https://corpusfetch.com/c/what-cognitive-load-invariants-must-survive-when-an-instance-reasoning-budget-is-reallocated-mid-task.warrant.json
# Markdown SHA-256:   b521756430d8683b156d048220f9c089267a532ee0bf0ab9d6499cd4d9e9c1b0
# Code AST SHA-256:   8c927c48c60e31f7c9a13d931934227b99b989a3ff779f33af137efc0da089d7
# Verified Classes:   ReallocationVerdict, BudgetReallocation, ReallocationPolicy, ReallocationManifest, BudgetReallocationGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

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

class ReallocationVerdict(Enum):
    NO_REALLOCATION = auto()
    REALLOCATION_CAPTURED = auto()
    SNAPSHOT_MISSING = auto()
    CONFIDENCE_UNATTRIBUTED = auto()

@dataclass(frozen=True)
class BudgetReallocation:
    reallocation_id: str
    original_budget: int
    new_budget: int
    reallocation_epoch: float
    in_progress_reasoning_hash: str | None
    cause: str
    confidence_at_cut: float | None

@dataclass(frozen=True)
class ReallocationPolicy:
    require_snapshot: bool
    require_confidence_attribution: bool

@dataclass(frozen=True)
class ReallocationManifest:
    verdict: ReallocationVerdict
    directive: str
    manifest_digest: str

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

    @classmethod
    def evaluate_reallocation(
        cls, realloc: BudgetReallocation | None, policy: ReallocationPolicy
    ) -> ReallocationManifest:
        
        # Gate 1: No reallocation
        if realloc is None:
            digest = cls._hash(json.dumps({
                "status": "NO_REALLOCATION"
            }, sort_keys=True))
            return ReallocationManifest(
                verdict=ReallocationVerdict.NO_REALLOCATION,
                directive="PROCEED: No budget reallocation occurred.",
                manifest_digest=digest
            )

        # Gate 2: Reallocation increased budget (benign)
        if realloc.new_budget >= realloc.original_budget:
            digest = cls._hash(json.dumps({
                "reallocation": realloc.reallocation_id,
                "direction": "INCREASE"
            }, sort_keys=True))
            return ReallocationManifest(
                verdict=ReallocationVerdict.NO_REALLOCATION,
                directive="PROCEED: Budget increased, no truncation risk.",
                manifest_digest=digest
            )

        # Gate 3: Snapshot requirement
        if policy.require_snapshot and not realloc.in_progress_reasoning_hash:
            return ReallocationManifest(
                verdict=ReallocationVerdict.SNAPSHOT_MISSING,
                directive=f"HALT: Budget cut on {realloc.reallocation_id} without reasoning snapshot.",
                manifest_digest=cls._hash(f"NO_SNAPSHOT:{realloc.reallocation_id}")
            )

        # Gate 4: Confidence attribution
        if policy.require_confidence_attribution and realloc.confidence_at_cut is None:
            return ReallocationManifest(
                verdict=ReallocationVerdict.CONFIDENCE_UNATTRIBUTED,
                directive=f"HALT: Confidence at cut not recorded for {realloc.reallocation_id}.",
                manifest_digest=cls._hash(f"NO_CONF:{realloc.reallocation_id}")
            )

        # Gate 5: Captured
        digest = cls._hash(json.dumps({
            "reallocation": realloc.reallocation_id,
            "original": str(realloc.original_budget),
            "new": str(realloc.new_budget),
            "cause": realloc.cause,
            "snapshot": realloc.in_progress_reasoning_hash,
            "confidence_at_cut": f"{realloc.confidence_at_cut:.3f}" if realloc.confidence_at_cut else "NONE"
        }, sort_keys=True))
        
        return ReallocationManifest(
            verdict=ReallocationVerdict.REALLOCATION_CAPTURED,
            directive=f"PROCEED: Reallocation {realloc.reallocation_id} captured with snapshot and confidence.",
            manifest_digest=digest
        )