feat(metadata): overview falls back to Chinese variants only (MD-2)

- adapters: overviewLanguages() limits overview/tagline chain to Chinese
  variants (zh-CN→zh-SG→zh-TW→zh-HK); titles keep full chain; season
  supplement fetch skips languages useless for overview
- setting metadata.overviewNonChineseFallback (default off) + UI switch
- media detail shows "暂无简介" for empty entity/episode overview
- scripts/overview-recompute.ts: recompute stored non-Chinese overviews
  from kv_cache only (no TMDB requests), dry-run by default, --apply
- tests: chain unit tests, Heart Signal (103147) fixture, server
  recompute test, MP differential for episode overview
- runbook + CHANGELOG

Co-Authored-By: Claude Opus 5.5 <[email protected]>

packages/adapters/test/differential/tmdb-overview.test.ts

@@ -0,0 +1,76 @@
+/**
+ * 每集简介差分(MD-2):MP `TmdbApi.get_tv_season_detail`(e6820a8,app/modules/themoviedb/tmdbapi.py)只按配置语言
+ * (TMDB_LOCALE = zh)请求季详情,episodes[].overview 原样使用,为空就为空;本项目 `fetchRichSeason` 按语言链补拉。
+ * 响应按《心动的信号》(TMDB tv/103147)各语言季详情的真实形态裁剪(每期标题有 zh-CN,简介只有 en-US)。
+ * 期望:简介与 MP 一致(中文变体都没有 → 空);标题允许按链回退(登记偏离 intentional:MD-1 占位集名按链补标题)。
+ */
+import { describe, expect, it } from "vitest";
+import { fetchRichSeason } from "../../src/tmdb/index.ts";
+
+type Ep = { episode_number: number; air_date: string; name: string; overview: string };
+const season = (episodes: Ep[]) => ({
+  season_number: 1,
+  name: "第 1 季",
+  overview: "",
+  air_date: "2018-08-01",
+  episodes,
+});
+
+/** 各语言的 /tv/103147/season/1 响应(裁剪) */
+const RECORDED: Record<string, ReturnType<typeof season>> = {
+  "zh-CN": season([
+    { episode_number: 1, air_date: "2018-08-01", name: "心动不如行动，大胆亮出底牌！", overview: "" },
+    { episode_number: 2, air_date: "2018-08-08", name: "第 2 集", overview: "" },
+  ]),
+  "zh-SG": season([
+    { episode_number: 1, air_date: "2018-08-01", name: "第 1 集", overview: "" },
+    { episode_number: 2, air_date: "2018-08-08", name: "第 2 集", overview: "" },
+  ]),
+  "zh-TW": season([
+    { episode_number: 1, air_date: "2018-08-01", name: "第 1 集", overview: "" },
+    { episode_number: 2, air_date: "2018-08-08", name: "第 2 集", overview: "" },
+  ]),
+  "zh-HK": season([
+    { episode_number: 1, air_date: "2018-08-01", name: "第 1 集", overview: "" },
+    { episode_number: 2, air_date: "2018-08-08", name: "第 2 集", overview: "" },
+  ]),
+  "en-US": season([
+    {
+      episode_number: 1,
+      air_date: "2018-08-01",
+      name: "Episode 1",
+      overview: "If Your Heart Skips a Beat, Play Your Cards Openly!",
+    },
+    { episode_number: 2, air_date: "2018-08-08", name: "Who Is the One?", overview: "Who Is the One?" },
+  ]),
+};
+
+const client = {
+  getJson: <T>(_path: string, params: Record<string, string | undefined> = {}) =>
+    Promise.resolve(RECORDED[params.language ?? "en-US"] as T),
+};
+
+/** MP 侧:只取配置语言(zh-CN)的季详情,集名 / 简介原样(空串 = 没有) */
+function mpEpisodes(lang = "zh-CN") {
+  return RECORDED[lang]!.episodes.map((e) => ({ ep: e.episode_number, name: e.name, overview: e.overview || null }));
+}
+
+const CHAIN = ["zh-CN", "zh-SG", "zh-TW", "zh-HK", "en-US"];
+const DEVIATIONS: Record<string, { kind: "intentional"; note: string }> = {
+  "E2.name": { kind: "intentional", note: "MD-1:zh-CN 是占位名「第 2 集」时按链补标题(可到 en-US)" },
+};
+
+describe("每集简介差分(MP get_tv_season_detail ↔ fetchRichSeason)", () => {
+  it("简介与 MP 一致:中文变体都没有时为空,不回退英文;标题偏离已登记", async () => {
+    const ours = await fetchRichSeason(client, 103147, 1, CHAIN, { now: new Date("2026-01-01") });
+    const mismatches: string[] = [];
+    for (const mp of mpEpisodes()) {
+      const e = ours.episodes.find((x) => x.episodeNumber === mp.ep)!;
+      if (e.overview !== mp.overview) mismatches.push(`E${mp.ep}.overview`);
+      if (e.name !== mp.name) mismatches.push(`E${mp.ep}.name`);
+    }
+    expect(mismatches.filter((m) => !DEVIATIONS[m])).toEqual([]);
+    expect(Object.keys(DEVIATIONS).every((k) => mismatches.includes(k))).toBe(true);
+    expect(ours.episodes.map((e) => e.overview)).toEqual([null, null]);
+  });
+});