memory: 修注入开销、idf 排序与抽取诊断

注入侧
- context 在每次模型请求都触发，改为按 session + 最新用户消息去重：
  一个 turn 里 n 次工具调用不再重复注入 n 个 memory 块
- 默认注入从 1200 字符 / 内联 4 条正文，降到 600 字符 / 内联 0 条：
  大纲已说明存在什么，正文交给 memory_recall 按需取一次，避免每次
  请求都为同一批正文付费
- halfLifeDays 此前被静默丢弃，注入始终按 14 天半衰期排序，现已接通
- 召回缓存 2s -> 500ms，同一工具链里 remember -> recall 能读到刚写的文件

排序
- idf 原先拿「单文件匹配数」当分子、「总文件数」当分母，每个文件得到
  相同 idf，排序退化为纯词频；改为按文档频率计算的真实 idf

抽取
- 移除 400 段上限：它会静默截断长对话，300 轮只贡献前 ~50 轮
- role 在顶层或 message 下两种返回结构都读，之前只读 .role 得到空转录，
  长度门槛不过，抽取看起来永远不触发
- 去重改按关键词重叠计分，不再用 bigram 重叠：模型改写与人工措辞几乎
  不共享 bigram，真实改写只拿到 0.43；关键词是双方被迫共用的词汇
- 新增 memory_extract_dryrun：对真实模型跑完整抽取链路，不必改
  minTurns 或等长会话
- 新增 memory_inspect：诊断记录按 scope 存入 storage key，并保留历史
  与 fires/injected 计数，去重是否生效可被证伪

其他
- Context 改从 Plugin 命名空间导入，此前类型退化为 unknown
- store 暴露 kind 字段；compileRootTables 内联进 compileRoot
- frontmatter 列表元素统一 String()，index 不再出现数字

验证：由仓库所有者端到端验证（真实模型调用、真实会话）；提交者未复跑，
以上为 diff 复核结论。

plugins/memory/store.ts

@@ -45,8 +45,10 @@ export interface MemoryFile {
   readonly title: string
   /** One-line description shown in indexes and injected summaries. */
   readonly summary: string
-  /** The "重点" column in index.md. */
+  /** Highlight column in index.md. */
   readonly highlight: string
+  /** `kind` from frontmatter, e.g. "fact", "rule", "rule-proposal". */
+  readonly kind?: string
   /** Scenarios that should pull this file in. Drives ROOT's routing table. */
   readonly loadWhen: string[]
   readonly pinned: boolean
@@ -170,6 +172,7 @@ function readMemoryFile(root: MemoryRoot, abs: string, category: string, name: s
     title: String(data.title ?? firstHeading(body) ?? slug),
     summary: String(data.summary ?? deriveSummary(body, slug)),
     highlight: String(data.highlight ?? ""),
+    kind: data.kind === undefined ? undefined : String(data.kind),
     loadWhen: toStringArray(data.load_when ?? data.loadWhen),
     pinned: data.pinned === true || data.pinned === "true",
     created: toNumber(data.created) ?? stat.mtimeMs,
@@ -431,12 +434,21 @@ function pruneEmptyIndexes(root: MemoryRoot, files: MemoryFile[]): void {
   }
 }
 
-export interface CompiledRoot {
-  registry: string
-  routing: string
+function describeCategory(category: string, files: MemoryFile[]): string {
+  const pinned = files.find((f) => isHardRule(f))
+  if (pinned && category === HARD_RULES_CATEGORY) return "不可违反的硬规则，常驻"
+  const first = files[0]
+  if (first?.fm.category_desc) return String(first.fm.category_desc)
+  return first ? first.summary.slice(0, 40) : "（空）"
 }
 
-export function compileRootTables(root: MemoryRoot, files: MemoryFile[]): CompiledRoot {
+/** Recompile ROOT.md's generated regions and write it if it does not exist. */
+export function compileRoot(root: MemoryRoot, files: MemoryFile[]): string {
+  // Same reason as the category index: ROOT.md may be the first thing written
+  // into a root that does not exist yet.
+  fs.mkdirSync(root.dir, { recursive: true })
+  const target = path.join(root.dir, "ROOT.md")
+
   const categories = groupByCategory(files)
 
   const registryRows = categories.map(({ category, files: list }) => {
@@ -461,25 +473,6 @@ export function compileRootTables(root: MemoryRoot, files: MemoryFile[]): Compil
     ? `\n| 场景 / 触发 | 读哪个文件 | 类型 |\n|---|---|---|\n${routingRows.join("\n")}\n`
     : `\n_暂无 load_when 标记的记忆。给文件加 frontmatter 的 \`load_when:\` 即可自动进入路由表。_\n`
 
-  return { registry, routing }
-}
-
-function describeCategory(category: string, files: MemoryFile[]): string {
-  const pinned = files.find((f) => isHardRule(f))
-  if (pinned && category === HARD_RULES_CATEGORY) return "不可违反的硬规则，常驻"
-  const first = files[0]
-  if (first?.fm.category_desc) return String(first.fm.category_desc)
-  return first ? first.summary.slice(0, 40) : "（空）"
-}
-
-/** Recompile ROOT.md's generated regions and write it if it does not exist. */
-export function compileRoot(root: MemoryRoot, files: MemoryFile[]): string {
-  // Same reason as the category index: ROOT.md may be the first thing written
-  // into a root that does not exist yet.
-  fs.mkdirSync(root.dir, { recursive: true })
-  const target = path.join(root.dir, "ROOT.md")
-  const { registry, routing } = compileRootTables(root, files)
-
   let existing: string | undefined
   try {
     existing = fs.readFileSync(target, "utf8")