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/client/Sidebar.tsx

@@ -32,7 +32,7 @@ import { IconCloseFill14, Tooltip } from '@deepseek-ai/dsh-client-ui-primitives'
 import type { Context, SidebarSessionList } from '../context-types.ts'
 import { appendToDraft } from './conversation-draft.ts'
 import {
-  BOTTOM_MIN, PANEL_MIN, agentUuidOf, closeTab, firstLeaf, isAgentTabId, leafWithTab, mapLeaf, migrateBottomTabs, moveTab, moveTabToEdge, openDiffTab,
+  BOTTOM_MIN, PANEL_MIN, agentUuidOf, firstLeaf, isAgentTabId, leafWithTab, migrateBottomTabs, moveTab, moveTabToEdge, openDiffTab,
   reconcileAgentTerminals,
   resizeSplitIn, setBottomHeight, setWidth, toggleBottomPanel, toggleExpanded, togglePanel,
   type DropZone, type SidebarState, type SidebarStore, type SidebarTab, type SplitNode,
@@ -555,7 +555,9 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
       const current = store.getSnapshot().state
       const leaf = current === undefined ? undefined : leafWithTab(current.splits, tabId)
       const tab = leaf?.tabs.find(candidate => candidate.id === tabId)
-      store.reduce(s => closeTab(s, paneId, tabId))
+      // Route through the service: the tab-bar close is the canonical close
+      // path (finds the pane itself, fires descriptor.onClose).
+      ctx.betterSidebar?.closeTab(tabId)
       if (tab?.type === 'terminal') {
         if (isAgentTabId(tabId)) {
           const uuid = agentUuidOf(tabId)
@@ -566,13 +568,9 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
       }
     },
     activateTab: (paneId, tabId) => {
-      store.reduce(s => ({
-        ...s,
-        activePane: paneId,
-        splits: mapLeaf(s.splits, paneId, (leaf) => {
-          if (leaf.tabs.some(tab => tab.id === tabId)) leaf.active = tabId
-        }),
-      }))
+      // Route through the service: same reducer (finds the pane in EITHER
+      // tree, sets the active pane) and fires descriptor.onActivate.
+      ctx.betterSidebar?.activateTab(tabId)
     },
     focusPane: (paneId) => { store.reduce(s => ({ ...s, activePane: paneId })) },
     moveTabToEdge: (payload: TabDragPayload, toPane: string, zone: DropZone) => {
@@ -631,7 +629,9 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
     const descriptor = service?.getTab(optionId)
     if (descriptor === undefined) return
     const title = typeof descriptor.title === 'function' ? descriptor.title() : descriptor.title
-    service.openTab({ type: optionId, title })
+    // The session scope rides along: lifecycle callbacks receive it (and
+    // the open stays in the current session, as before).
+    service.openTab({ type: optionId, title }, { sessionId, cwd })
   }
 
   /**
@@ -647,6 +647,26 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
     return typeof descriptor.icon === 'function' ? descriptor.icon(14) : descriptor.icon
   }
 
+  /**
+   * The tab badge from the tab-type registry: a count (99+ capped) or a
+   * short text pill. A throwing badge is swallowed (no pill) — the tab
+   * strip must never break because a plugin's badge computation failed.
+   */
+  const tabBadgeOf = (tab: SidebarTab): ReactNode => {
+    const descriptor = ctx.betterSidebar?.getTab(tab.type)
+    if (descriptor?.badge === undefined) return null
+    let value: string | number | null | undefined
+    try {
+      value = descriptor.badge(ctx, { sessionId, cwd }, state)
+    } catch (error) {
+      console.error('[dsh-better-sidebar] tab badge error:', error)
+      return null
+    }
+    if (value === null || value === undefined || value === '') return null
+    const text = typeof value === 'number' ? (value > 99 ? '99+' : String(value)) : String(value)
+    return <span className={css.tabBadge}>{text}</span>
+  }
+
   /**
    * Render one tab's content. `active` (from the workbench) tells whether
    * this tab is the active one in its pane; combined with the panel's
@@ -757,6 +777,7 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
             onNewTab={onNewTab}
             renderTab={renderTab}
             getTabIcon={tabIconOf}
+            getTabBadge={tabBadgeOf}
           />
         </div>
       </div>
@@ -836,6 +857,7 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
             onNewTab={onNewTab}
             renderTab={(tab, active, paneId) => renderTab(tab, active, paneId, true)}
             getTabIcon={tabIconOf}
+            getTabBadge={tabBadgeOf}
           />
         </div>
       </div>