feat: 公共 API 基座化（v0.12.0，纯增量）— 类型/能力/设置 seam 全面补齐

- 类型生态：service 模块 re-export SidebarTab/SidebarState/SidebarStore/
  SidebarSnapshot/SidebarDiffRef/TabType/SessionScope/SidebarPrefs 等公共
  状态词汇（此前 TS2459 无法命名）；context-types 去 Node 依赖（结构镜像
  SidebarHttpRequest/Response/UpgradeSocket/Head），client 可达声明图零
  node:* 引用，外部消费者无 @types/node + skipLibCheck:false 可编译
  （scripts/check-consumer-types.sh 守护）
- 服务能力：version/features 版本与能力探测（单调只增）、getSnapshot/
  subscribeState 状态订阅、updateTab（title/path/meta）、activateTab、
  openFile（路径派生 id 与内置拦截一致）、openTab(seed, scope?) 定向到
  指定 session（store.reduceFor 不扰动 UI）
- TabDescriptor：badge 角标（99+ 封顶，抛错吞掉）、onOpen/onActivate/
  onClose 生命周期回调（service 路径派发，dedupe 聚焦触发 onActivate
  而非 onOpen，抛错不打断流程）；SidebarTab.meta JSON 可序列化跨刷新
  持久化（sanitize 宽松保留）
- 设置 seam 开放：PrefsSchema 增 pluginSettings 开放嵌套 map（z.dict），
  settings.pluginToggles（插件自有行，同 switch/text/number 控件）与
  settings.render（自定义面板，含 store/service/prefs/updatePluginSetting/
  close props）；viewer 卡片 v0.12.0 起也有齿轮设置弹窗
- FileViewerDescriptor.load 增第三参 AbortSignal（EditorHost 生命周期中止）
- UI 接线：tab 激活/关闭改走 service（跨树激活修复 + 回调触发）、+ 菜单
  传 scope、TabBar badge pill 渲染；active-session scope 走原 reduce 路径
  保证 notify
- 测试 +23：生命周期/定向打开/updateTab/activateTab/openFile/meta 持久化/
  reduceFor/能力常量（与 package.json 锁步）、consumer-types.ts 编译门、
  api-surface.spec.ts（client 图零 node 依赖守护）；既有 430 测试全绿
- 文档：AGENTS.md 修 available 三参示例并补全部新 API；external-plugin-
  guide.md 刷新至 v0.12.0（7 tab + 9 viewer、设置 seam 开放、类型导入
  路径建议）；README×2 服务化小节同步

未发版 npm（用户决定）；分支 feat/plugin-api-v012。

src/context-types.ts

@@ -16,23 +16,56 @@
  * - slots: the client runtime SlotRegistry
  * - effect: the DSH-vendored cordis lifecycle helper
  * Drift from upstream is contained to this file.
+ *
+ * This file must stay FREE of Node.js types (`node:http`, `node:stream`,
+ * `Buffer`): it is part of the CLIENT-reachable declaration graph (the
+ * `Context` in `TabComponentProps` and the `declare module` augmentation),
+ * so a Node import here would leak into browser-only consumer builds. The
+ * webServer faces below are therefore structural mirrors with plain
+ * interfaces (the host casts to real Node types at the few boundaries that
+ * need them — e.g. the `ws` upgrade hook in src/index.ts).
  */
-import type { IncomingMessage, ServerResponse } from 'node:http'
-import type { Duplex } from 'node:stream'
 import type { Context } from 'cordis'
 import type { BetterSidebarService } from './client/service.ts'
 
+/** The request face route handlers see (structural subset of node's
+ *  IncomingMessage: the URL/method/header reads and the async body
+ *  iteration `readJsonBody` uses). */
+export interface SidebarHttpRequest {
+  url?: string
+  method?: string
+  headers: Record<string, string | string[] | undefined>
+  [Symbol.asyncIterator](): AsyncIterator<string | Uint8Array>
+}
+
+/** The response face route handlers write to (structural subset of node's
+ *  ServerResponse: the status/header/body writes the routes use). */
+export interface SidebarHttpResponse {
+  statusCode: number
+  writeHead(status: number, headers?: Record<string, string>): void
+  end(body?: string | Uint8Array): void
+}
+
+/** The upgrade socket face (structural subset: the destroy the fences use). */
+export interface SidebarUpgradeSocket {
+  destroy(): void
+}
+
+/** The upgrade head bytes (Buffer at runtime; typed as bytes so no Node
+ *  global leaks into the declaration graph). */
+export type SidebarUpgradeHead = Uint8Array
+
 /** One named webserver route (mirror of the host-webserver WebRoute). */
 export interface SidebarWebRoute {
   kind: 'exact' | 'prefix'
   path: string
-  handler: (req: IncomingMessage, res: ServerResponse) => void | Promise<void>
+  handler: (req: SidebarHttpRequest, res: SidebarHttpResponse) => void | Promise<void>
 }
 
 /** One exact-path HTTP upgrade registration (mirror of WebUpgradeRoute). */
 export interface SidebarWebUpgradeRoute {
   path: string
-  handler: (req: IncomingMessage, socket: Duplex, head: Buffer) => void | Promise<void>
+  handler: (req: SidebarHttpRequest, socket: SidebarUpgradeSocket, head: SidebarUpgradeHead) => void | Promise<void>
 }
 
 /** The webServer service face this plugin uses. */