life-echo/api/app/features/memoir/narrative_safety.py

"""叙事落库前的确定性安检：防止 prompt 分区标记或摘录块泄漏进正文。"""

from __future__ import annotations

# 与 app.agents.memoir.prompts.format_narrative_user_content 保持一致
ORAL_SECTION_MARKER = "【本段用户口述】"
EVIDENCE_SECTION_MARKER = "【仅供参考的相关记忆摘录"

# 摘录引导语中的固定短语（用于粗检）
EVIDENCE_SECTION_TAIL = "不得把其中具体事实写成本轮亲历经历"


def body_contains_prompt_artifact(markdown_body: str) -> bool:
    s = (markdown_body or "").strip()
    if not s:
        return False
    if ORAL_SECTION_MARKER in s:
        return True
    if EVIDENCE_SECTION_MARKER in s:
        return True
    if EVIDENCE_SECTION_TAIL in s:
        return True
    return False


def longest_common_substring_len(a: str, b: str, min_len: int = 14) -> int:
    """O(n*m) DP；仅用于短 evidence / body，防止过大。"""
    a = a or ""
    b = b or ""
    if len(a) > 8000 or len(b) > 8000:
        return 0
    if not a or not b:
        return 0
    best = 0
    prev = [0] * (len(b) + 1)
    for i in range(1, len(a) + 1):
        cur = [0] * (len(b) + 1)
        for j in range(1, len(b) + 1):
            if a[i - 1] == b[j - 1]:
                cur[j] = prev[j - 1] + 1
                if cur[j] > best:
                    best = cur[j]
            else:
                cur[j] = 0
        prev = cur
    return best if best >= min_len else 0


def evidence_substring_leak_score(
    body: str, evidence_plain: str, min_len: int = 14
) -> int:
    """
    若正文与 evidence 存在较长公共子串，且该子串不在 oral/existing 中，
    则视为摘录渗漏风险（返回子串长度），否则 0。
    """
    body = (body or "").strip()
    ev = (evidence_plain or "").strip()
    if not body or not ev or len(ev) < min_len:
        return 0
    return longest_common_substring_len(body, ev, min_len=min_len)


def longest_common_substring(a: str, b: str) -> str:
    """返回 a、b 的最长公共子串（长度上限防 DP 爆内存）。"""
    a = a or ""
    b = b or ""
    if len(a) > 8000 or len(b) > 8000:
        return ""
    best_i, best_len = 0, 0
    prev = [0] * (len(b) + 1)
    for i in range(1, len(a) + 1):
        cur = [0] * (len(b) + 1)
        for j in range(1, len(b) + 1):
            if a[i - 1] == b[j - 1]:
                cur[j] = prev[j - 1] + 1
                if cur[j] > best_len:
                    best_len = cur[j]
                    best_i = i
            else:
                cur[j] = 0
        prev = cur
    if best_len <= 0:
        return ""
    start = best_i - best_len
    return a[start:best_i]


# 具体场合描写：易由「相关摘录」渗入正文但长 LCS 抓不住（词短）。
EVIDENCE_SCENE_ANCHOR_TOKENS: tuple[str, ...] = (
    "聚餐",
    "酒席",
    "酒桌",
    "宴会",
    "宴席",
    "当晚",
    "那晚",
    "昨夜",
    "前一晚",
    "前一天晚上",
)


def evidence_scene_anchor_leak(
    body: str,
    evidence_plain: str,
    oral: str,
    existing: str,
) -> bool:
    """
    True：正文出现了与「摘录」共享的具体场合锚点词，且口述与旧正文均未出现，
    视为摘录场景渗漏（短词不走 LCS 阈值）。
    """
    body = (body or "").strip()
    ev = (evidence_plain or "").strip()
    o = (oral or "").strip()
    ex = (existing or "").strip()
    if not body or not ev:
        return False
    base = f"{o}\n{ex}"
    for tok in EVIDENCE_SCENE_ANCHOR_TOKENS:
        if tok not in body:
            continue
        if tok in base:
            continue
        if tok in ev:
            return True
    return False


def evidence_leakage_heuristic(
    body: str,
    evidence_plain: str,
    oral: str,
    existing: str,
    min_len: int,
) -> bool:
    """
    True：正文与 evidence 的最长公共子串足够长，且该子串未出现在口述或已有正文中，
    视为摘录渗漏，应回退安全正文。
    """
    body = (body or "").strip()
    ev = (evidence_plain or "").strip()
    if not body or not ev:
        return False
    lcs = longest_common_substring(body, ev)
    if len(lcs) < min_len:
        return False
    o = oral or ""
    ex = existing or ""
    if lcs in o or lcs in ex:
        return False
    return True


def strip_evidence_for_overlap_check(evidence_text: str) -> str:
    """去掉 chunk 标记行等噪声，仅保留内容用于 overlap。"""
    lines: list[str] = []
    for line in (evidence_text or "").splitlines():
        t = line.strip()
        if t.startswith("[chunk_id="):
            continue
        if t.startswith("[摘要:"):
            continue
        lines.append(line)
    return "\n".join(lines).strip()