# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/what-minimum-viable-reasoning-survives-when-the-reasoning-budget-collapses-mid-task.md
# Remnant Warrant:    https://corpusfetch.com/c/what-minimum-viable-reasoning-survives-when-the-reasoning-budget-collapses-mid-task.warrant.json
# Markdown SHA-256:   a9a4f3d31cbed7f41e0ce789ed6347e6aa828307b76a8fb34524b042cb96fbd2
# Code AST SHA-256:   37c66756b78e5b0a5f1aadea511eb18f98fe7e66de0c95db89de411ded0469c7
# Verified Classes:   BudgetVerdict, BudgetState, BudgetPolicy, BudgetManifest, ReasoningBudgetCollapseGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

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

class BudgetVerdict(Enum):
    NO_COLLAPSE = auto()
    MINIMUM_VIABLE_PRODUCED = auto()
    SCOPE_REDUCTION_UNDECLARED = auto()
    INSUFFICIENT_FOR_VIABLE = auto()

@dataclass(frozen=True)
class BudgetState:
    state_id: str
    budget_collapsed: bool
    residual_budget_ratio: float
    minimum_viable_scope_defined: bool
    scope_declared: bool

@dataclass(frozen=True)
class BudgetPolicy:
    min_viable_threshold: float

@dataclass(frozen=True)
class BudgetManifest:
    verdict: BudgetVerdict
    directive: str
    manifest_digest: str

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

    @classmethod
    def evaluate_state(
        cls, state: BudgetState, policy: BudgetPolicy
    ) -> BudgetManifest:
        
        # Gate 1: No collapse
        if not state.budget_collapsed:
            digest = cls._hash(json.dumps({
                "state": state.state_id,
                "collapsed": False
            }, sort_keys=True))
            return BudgetManifest(
                verdict=BudgetVerdict.NO_COLLAPSE,
                directive=f"PROCEED: State {state.state_id} budget intact.",
                manifest_digest=digest
            )

        # Gate 2: Insufficient for viable
        if state.residual_budget_ratio < policy.min_viable_threshold:
            return BudgetManifest(
                verdict=BudgetVerdict.INSUFFICIENT_FOR_VIABLE,
                directive=f"HALT: State {state.state_id} residual {state.residual_budget_ratio:.2f} below viable threshold.",
                manifest_digest=cls._hash(f"INSUFFICIENT:{state.state_id}")
            )

        # Gate 3: Scope reduction undeclared
        if not state.scope_declared:
            return BudgetManifest(
                verdict=BudgetVerdict.SCOPE_REDUCTION_UNDECLARED,
                directive=f"HALT: State {state.state_id} scope reduced without declaration.",
                manifest_digest=cls._hash(f"UNDECLARED:{state.state_id}")
            )

        # Gate 4: Minimum viable produced
        digest = cls._hash(json.dumps({
            "state": state.state_id,
            "residual": f"{state.residual_budget_ratio:.3f}",
            "scope": "REDUCED"
        }, sort_keys=True))
        
        return BudgetManifest(
            verdict=BudgetVerdict.MINIMUM_VIABLE_PRODUCED,
            directive=f"PROCEED: State {state.state_id} minimum viable produced.",
            manifest_digest=digest
        )