# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/how-should-agents-detect-and-recover-from-silent-partial-results-during-streaming-inference.md
# Remnant Warrant:    https://corpusfetch.com/c/how-should-agents-detect-and-recover-from-silent-partial-results-during-streaming-inference.warrant.json
# Markdown SHA-256:   b3783eeeb8e07aecb6c17d548697e2fe5d098467a6f5e8a44e382f4ff27eaf1c
# Code AST SHA-256:   35491cfc154d7fe3080ec33bdc012beec5ab0692db0bdc56cb8013b1950e2dca
# Verified Classes:   PartialStreamVerdict, StreamState, StreamPolicy, StreamManifest, PartialStreamGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

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

class PartialStreamVerdict(Enum):
    COMPLETE_EXPLICIT = auto()
    COMPLETE_BY_LENGTH = auto()
    PARTIAL_MID_TOKEN = auto()
    PARTIAL_SAFE_BOUNDARY = auto()

@dataclass(frozen=True)
class StreamState:
    completion_signal_present: bool
    expected_length: int | None
    received_length: int
    terminal_byte_is_safe_boundary: bool

@dataclass(frozen=True)
class StreamPolicy:
    accept_partial_at_safe_boundary: bool

@dataclass(frozen=True)
class StreamManifest:
    verdict: PartialStreamVerdict
    directive: str
    manifest_digest: str

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

    @classmethod
    def evaluate_stream(
        cls, state: StreamState, policy: StreamPolicy
    ) -> StreamManifest:
        
        # Gate 1: Explicit completion
        if state.completion_signal_present:
            digest = cls._hash(json.dumps({
                "received": str(state.received_length),
                "completion": "EXPLICIT"
            }, sort_keys=True))
            return StreamManifest(
                verdict=PartialStreamVerdict.COMPLETE_EXPLICIT,
                directive="PROCEED: Stream complete with explicit signal.",
                manifest_digest=digest
            )

        # Gate 2: Length match
        if state.expected_length is not None and state.received_length == state.expected_length:
            digest = cls._hash(json.dumps({
                "received": str(state.received_length),
                "expected": str(state.expected_length),
                "completion": "BY_LENGTH"
            }, sort_keys=True))
            return StreamManifest(
                verdict=PartialStreamVerdict.COMPLETE_BY_LENGTH,
                directive=f"PROCEED: Stream length matches expected {state.expected_length}.",
                manifest_digest=digest
            )

        # Gate 3: Safe boundary
        if state.terminal_byte_is_safe_boundary and policy.accept_partial_at_safe_boundary:
            digest = cls._hash(json.dumps({
                "received": str(state.received_length),
                "boundary": "SAFE"
            }, sort_keys=True))
            return StreamManifest(
                verdict=PartialStreamVerdict.PARTIAL_SAFE_BOUNDARY,
                directive="PROCEED_WITH_CAUTION: Partial stream at safe boundary. Verify downstream.",
                manifest_digest=digest
            )

        # Gate 4: Mid-token partial
        return StreamManifest(
            verdict=PartialStreamVerdict.PARTIAL_MID_TOKEN,
            directive="HALT: Stream truncated mid-token. Re-fetch or repair.",
            manifest_digest=cls._hash(f"MID_TOKEN:{state.received_length}")
        )