refactor(engine): remove follow-up choices from insert-beat, keep multi-beat only

Insert-beat is a pure in-scene micro-interaction — adding choices that
lead to change-scene contradicted its purpose. Now insert-beat generates
1-3 richer beats then loops back to the original options, which is the
natural UX for "you glanced at something decorative."

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/engine/director.ts

@@ -578,6 +578,9 @@ function coerceBeatPartial(raw: Record<string, unknown>): InsertBeatPartial | nu
       ? ((typeof raw.lineDelivery === "string" ? raw.lineDelivery.trim() : undefined) || undefined)
       : undefined;
   if (!narration && !speaker && !line) return null;
+  if (line && !speaker) {
+    return { narration: [narration, line].filter(Boolean).join("\n") || undefined };
+  }
   return { narration, speaker, line, lineDelivery };
 }
 
@@ -585,7 +588,7 @@ export async function directInsertBeat(
   config: ProviderConfig,
   session: Session,
   freeformAction: string,
-): Promise<{ beats: InsertBeatPartial[]; choices?: { label: string; effect: string }[] }> {
+): Promise<InsertBeatPartial[]> {
   const raw = await chat(
     config,
     [
@@ -600,25 +603,23 @@ export async function directInsertBeat(
 
   const parsed = parseJsonLoose<InsertBeatMulti & InsertBeatPartial>(raw);
 
-  // New multi-beat format: { beats: [...], choices: [...] }
+  // Multi-beat format: { beats: [...] }
   if (Array.isArray(parsed.beats) && parsed.beats.length > 0) {
     const beats = parsed.beats
       .slice(0, 3)
-      .map((b) => coerceBeatPartial(b as Record<string, unknown>))
+      .map((b) =>
+        b && typeof b === "object"
+          ? coerceBeatPartial(b as Record<string, unknown>)
+          : null,
+      )
       .filter((b): b is InsertBeatPartial => b !== null);
     if (beats.length === 0) {
       beats.push({ narration: "（你停下脚步，环视片刻。）" });
     }
-    const choices = Array.isArray(parsed.choices)
-      ? parsed.choices
-          .filter((c) => c && typeof c.label === "string" && c.label.trim() && typeof c.effect === "string" && c.effect.trim())
-          .slice(0, 2)
-          .map((c) => ({ label: c.label.trim(), effect: c.effect.trim() }))
-      : undefined;
-    return { beats, choices: choices?.length ? choices : undefined };
+    return beats;
   }
 
   // Legacy single-beat fallback
   const single = coerceBeatPartial(parsed as Record<string, unknown>);
-  return { beats: [single ?? { narration: "（你停下脚步，环视片刻。）" }] };
+  return [single ?? { narration: "（你停下脚步，环视片刻。）" }];
 }

lib/engine/orchestrator.ts

@@ -203,7 +203,7 @@ export async function requestInsertBeat(
   );
 
   // Guard every beat: promote unregistered speakers to narration.
-  const guardedBeats = result.beats.map((partial) => {
+  const guardedBeats = result.map((partial) => {
     if (
       partial.speaker &&
       partial.speaker !== "你" &&
@@ -230,7 +230,6 @@ export async function requestInsertBeat(
   return {
     partial: first,
     extraBeats: extra.length > 0 ? extra : undefined,
-    followUpChoices: result.choices,
     characters: req.session.characters,
   };
 }

lib/engine/prompts.ts

@@ -572,7 +572,7 @@ STRICT RULES:
 //  Single-agent path; no character design / no rendering involved.
 // ──────────────────────────────────────────────────────────────────────
 
-export const INSERT_BEAT_SYSTEM = `你是视觉小说编剧。玩家在当前场景内做了一个自由动作（可能是点击画面中的某个物件/角色，也可能是主动输入了一句话/动作）。请基于此动作，写出**1-3 个有实质内容的 beat**，并在最后给出 2 个后续选项供玩家选择。
+export const INSERT_BEAT_SYSTEM = `你是视觉小说编剧。玩家在当前场景内做了一个自由动作（可能是点击画面中的某个物件/角色，也可能是主动输入了一句话/动作）。请基于此动作，写出**1-3 个有实质内容的 beat**。
 
 核心原则——**玩家的动作必须得到回应**：
 - 如果当前场景有 NPC 在场，NPC **必须对玩家的动作做出反应**（说话、表情变化、动作回应）。用 narration 描述玩家的动作，用 speaker + line 写 NPC 的回应。
@@ -584,15 +584,10 @@ beat 数量指引：
 - 有来有回的对话/有展开的互动：2-3 个 beat，让反应更有层次
 - 每个 beat 的 narration + line ≤100 字
 
-后续选项（choices）——每次**必须**给出 2 个选项：
-- 选项应**承接刚才的互动**，给玩家自然的下一步
-- 至少一个选项应能推动剧情前进（如"继续追问"、"走过去看看"、"做出某个决定"）
-- label：玩家看到的选项文字（≤15字）
-- effect：描述选这个选项后会发生什么（供下一个编剧参考）
-
 文本风格约束：
 - narration / line 用中文，**纯净可显示文本**，不要写 (叹气)(语速快) 这类配音标注
 - 不要打破当前场景的物理状态（玩家仍在原地）
+- 不要生成选项或下一步指引——播完后玩家会自然回到原来的选项
 - 内容要"有所得"——一个新细节、一丝潜台词、一次真实的交流（show, don't tell）
 - 白描为主：聚焦可观察的五感与物理特征，以角色的动作/神态本身传递情绪，不要以作者角度解释或议论；不写角色眼神/语气里的情绪（这些从台词与动作中自行体会）
 
@@ -615,10 +610,6 @@ speaker 字段允许的取值**只有两种**（与主路径 Writer 一致 — P
 {
   "beats": [
     { "narration": "...", "speaker": "...", "line": "...", "lineDelivery": "..." }
-  ],
-  "choices": [
-    { "label": "选项文字", "effect": "选此选项后的剧情走向" },
-    { "label": "选项文字", "effect": "选此选项后的剧情走向" }
   ]
 }
 
@@ -667,7 +658,7 @@ export function buildInsertBeatUserMessage(
   }
 
   parts.push(`\n玩家此刻的自由动作：${freeformAction}`);
-  parts.push("\n请生成 beat（1-3 个）和 2 个后续选项，严格以 JSON 格式返回。");
+  parts.push("\n请生成 1-3 个 beat，严格以 JSON 格式返回。");
   const langDirective = buildLanguageDirective(session.language);
   if (langDirective) parts.push(langDirective);
   return parts.join("\n");

lib/types/index.ts

@@ -695,19 +695,15 @@ export type InsertBeatPartial = {
   lineDelivery?: string;
 };
 
-/** Multi-beat response: 1-3 beats + optional follow-up choices. */
+/** Multi-beat response: 1-3 beats. */
 export type InsertBeatMulti = {
   beats: InsertBeatPartial[];
-  /** Follow-up choices shown after the last beat (max 2). */
-  choices?: { label: string; effect: string }[];
 };
 
 export type InsertBeatResponse = {
   partial: InsertBeatPartial;
   /** Additional beats beyond the first (for richer insert-beat interactions). */
   extraBeats?: InsertBeatPartial[];
-  /** Follow-up choices shown after the last inserted beat. */
-  followUpChoices?: { label: string; effect: string }[];
   characters: Character[];
 };