5.1 张力从哪里来：叙事节拍

#!/usr/bin/env python3
# file: sim/nm_05_1_beat_tension.py
# tier: S
# verify: /opt/homebrew/bin/python3 sim/nm_05_1_beat_tension.py
"""卷三 5.1 张力从哪里来：叙事节拍（S 层）。

张力在本卷里不是从机制里长出来的，而是作者在规格里**标注**的：config/story_spec.json
的 `beats` 是 16 个节拍，每个带 `tension`（整数 1–5）与 `scene`。本脚本只读这份标注，
不跑任何一局战斗，就能把整条张力序列、按幕聚合、分布直方图与峰值位置全部算出来——
这正说明「叙事张力」是一个**规格里的整数数组**，输入不是 HP / 资源 / 回合节奏。

产出 out/nm_05_1_beat_tension.json。全部定点整数，不出现浮点。
"""
from __future__ import annotations

import json
import os
import sys

HERE = os.path.dirname(os.path.abspath(__file__))
ROOT = os.path.dirname(HERE)
OUT = os.path.join(ROOT, "out")
TENSION_LO, TENSION_HI = 1, 5


def load_spec() -> dict:
    with open(os.path.join(ROOT, "config/story_spec.json"), encoding="utf-8") as fh:
        return json.load(fh)


def main() -> int:
    spec = load_spec()
    beats = spec["beats"]
    seq = [b["tension"] for b in beats]
    acts = sorted({b["act"] for b in beats})

    print(f"节拍数       {len(beats)}")
    print(f"张力序列     {' '.join(str(t) for t in seq)}")
    print(f"张力之和     {sum(seq)}")
    print(f"取值区间     {min(seq)}–{max(seq)}")

    per_act = []
    for a in acts:
        ts = [b["tension"] for b in beats if b["act"] == a]
        per_act.append({"act": a, "beats": len(ts), "sum": sum(ts),
                        "mean_permille": sum(ts) * 1000 // len(ts)})
        print(f"第 {a} 幕       {len(ts)} 拍  和 {sum(ts)}  均 {sum(ts) * 1000 // len(ts)} 毫")

    hist = {t: sum(1 for x in seq if x == t) for t in range(TENSION_LO, TENSION_HI + 1)}
    print(f"分布         {json.dumps(hist, ensure_ascii=False)}")

    peaks = [b["id"] for b in beats if b["tension"] == TENSION_HI]
    peak_scenes = [b["scene"] for b in beats if b["tension"] == TENSION_HI]
    print(f"峰值节拍     {' '.join(peaks)}（{len(peaks)} 个：{' '.join(peak_scenes)}）")

    assert all(TENSION_LO <= t <= TENSION_HI for t in seq), "张力越界"
    assert sum(seq) == 52, "张力之和应为 52"

    os.makedirs(OUT, exist_ok=True)
    report = {
        "beat_count": len(beats),
        "tension_sequence": seq,
        "tension_sum": sum(seq),
        "range": [min(seq), max(seq)],
        "per_act": per_act,
        "histogram": hist,
        "peaks": peaks,
        "peak_scenes": peak_scenes,
        "invariant_residual": 0,
    }
    with open(os.path.join(OUT, "nm_05_1_beat_tension.json"), "w", encoding="utf-8") as fh:
        json.dump(report, fh, ensure_ascii=False, indent=2)
        fh.write("\n")
    print("wrote out/nm_05_1_beat_tension.json")
    print(f"OK nm_05_1_beat_tension：{len(beats)} 个节拍，张力之和 {sum(seq)}，整数不变量残差 0")
    return 0


if __name__ == "__main__":
    sys.exit(main())

节拍数       16
张力序列     1 2 2 3 2 3 4 3 4 5 3 4 5 5 4 2
张力之和     52
取值区间     1–5
第 1 幕       5 拍  和 10  均 2000 毫
第 2 幕       6 拍  和 22  均 3666 毫
第 3 幕       5 拍  和 20  均 4000 毫
分布         {"1": 1, "2": 4, "3": 4, "4": 4, "5": 3}
峰值节拍     b10 b13 b14（3 个：drowned_bell breakwater fog_gate）
wrote out/nm_05_1_beat_tension.json
OK nm_05_1_beat_tension：16 个节拍，张力之和 52，整数不变量残差 0

{
  "section": "5.1",
  "source": "config/story_spec.json#beats",
  "tier": "D",
  "field_table": [
    {"field": "id", "type": "string", "note": "节拍标识 b01..b16"},
    {"field": "act", "type": "int", "note": "所属幕，1..3"},
    {"field": "scene", "type": "string", "note": "所属场景，与 scene_graph.nodes 对齐"},
    {"field": "tension", "type": "int", "note": "张力标注，取值 1..5，本卷曲线唯一输入"},
    {"field": "summary", "type": "string", "note": "一句话概述，仅供人读，不参与计算"}
  ],
  "tension_domain": [1, 5],
  "invariants": [
    "每个 tension 落在 [1,5] 闭区间",
    "16 个节拍 tension 之和恒为 52",
    "tension 为整数，config 层禁浮点"
  ],
  "scale": {"beats": 16, "tension_sum": 52, "peaks_at_5": 3},
  "proxy": "tension 是作者标注的相对强度，只用于相对比较，不声称任何绝对情绪量"
}