新增转述回合引擎，用插入工具把对话落成带相对序的产物。

Co-authored-by: Cursor <cursoragent@cursor.com>

src/dictate/context.ts

@@ -0,0 +1,64 @@
+import type { ChatMessage } from "../llm/client.js";
+import {
+  effectiveDictateOrder,
+  sortDictateProducts,
+  type DictateChatTurn,
+  type DictateProduct,
+} from "./types.js";
+
+/**
+ * 拼给模型的上下文：系统提示 + 全部产物（按相对序）+ 全量对话。
+ * 清空对话后，只剩产物块，产物即浓缩上下文。
+ */
+export function buildDictateMessages(params: {
+  systemPrompt: string;
+  products: DictateProduct[];
+  dialogue: DictateChatTurn[];
+}): ChatMessage[] {
+  const parts: string[] = [];
+  const products = sortDictateProducts(params.products);
+
+  if (products.length > 0) {
+    parts.push("## 当前产物（已写入黑板，按相对序；对话清空后仍保留）");
+    for (const p of products) {
+      const ord = effectiveDictateOrder(p);
+      parts.push(`### ${p.tag} 〔order=${ord}〕\n${p.content}`);
+    }
+  } else {
+    parts.push("## 当前产物\n（尚无）");
+  }
+
+  parts.push("## 对话（全量）");
+  if (params.dialogue.length === 0) {
+    parts.push("（尚无对话；等用户开口）");
+  } else {
+    for (const turn of params.dialogue) {
+      const who = turn.role === "user" ? "用户" : "助手";
+      parts.push(`【${who}】\n${turn.text}`);
+    }
+  }
+
+  return [
+    { role: "system", content: params.systemPrompt },
+    { role: "user", content: parts.join("\n\n") },
+  ];
+}
+
+/** 从会话消息里抽出转述式对话（用户输入 + 助手回复） */
+export function extractDictateDialogue(
+  messages: Array<{ role?: string; kind?: string; text?: string; body?: string }>,
+): DictateChatTurn[] {
+  const out: DictateChatTurn[] = [];
+  for (const m of messages) {
+    const text = (m.body ?? m.text ?? "").trim();
+    if (!text) continue;
+    if (m.role === "user" || m.kind === "user_input") {
+      out.push({ role: "user", text });
+      continue;
+    }
+    if (m.kind === "dictate_reply") {
+      out.push({ role: "assistant", text });
+    }
+  }
+  return out;
+}