fix(changes): 会话事件改走宿主 changes.ops 路由 + diff 展开二级设置 + 视觉迭代

CI 修复（plugin-mount 的 ctx.sessions.get TypeError ×1003）：
- 客户端 runtime 无事件日志面——badge/SessionLens 原在客户端直读
  ctx.sessions.get(id).events / ctx.on('session/event')，全部不可达。
- 新增宿主路由 changes.ops：live 会话日志优先，冷会话回放
  sessionPersistence.inspect；afterSeq 增量（缺省游标含 seq 0，
  显式游标为 seq > afterSeq，同 sidechat.events 约定），窗口上限
  4000 与客户端累加器一致。
- ChangesTab 轮询（mount 一拉 + visible 2.5s 增量）折入 ops，写
  模块级 opCounts 缓存供 badge 同步读取；SessionLens 改纯展示。

diff 展开二级设置（changesDiffFloat，默认浮窗）：
- prefs 四处接线 + git tab settings select（浮窗/面板，图标选项卡）
- 预览面板「展开为 diff tab」按设置落点：浮窗居中弹出或源 pane
  下方 split；i18n 全 21 词典同步。

视觉迭代（真机挂载截图审查后调整）：
- Session 视角：kind 徽章为左轨，大小+相对时间右对齐元列；失败
  操作行红色内嵌条；文件组头降为三级标签并加组间距。
- Git 视角：untracked '?' 徽章与新增同绿色；stage 按钮改 plus 图标。
- diff 折叠行：可展开折叠带 › 箭头 + 次级对比度，静态 gap 不再
  显示 pointer/hover；预览头路径改尾部截断（RTL 技巧，保文件名）。

验证：typecheck ✓ / vitest 1123 ✓ / pnpm test:mount（钉 alpha.2 CLI）
14/14 ✓；真机挂载截图（badge=5、双视角、浮窗展开）0 console error。

src/index.ts

@@ -18,7 +18,7 @@ import { basename, dirname, extname, isAbsolute, join } from 'node:path'
 import type { IncomingMessage } from 'node:http'
 import type { Duplex } from 'node:stream'
 import { WebSocket, WebSocketServer } from 'ws'
-import type { Context, SidebarHttpRequest } from './context-types.ts'
+import type { Context, SidebarHttpRequest, SidebarSessionEvent } from './context-types.ts'
 import {
   Config,
   PrefsSchema,
@@ -455,6 +455,44 @@ function buildApi(
       const rev = requireString(payload, 'rev')
       return { content: await git.show(cwd, rev, path, repoRoot) }
     },
+    // The session's file-tool events for the changes tab's session lens
+    // (and its badge): the CLIENT runtime's sessions face has no event-log
+    // access, so the events cross the wire here — live session log first,
+    // the persisted logical log for not-yet-hydrated sessions. Only the
+    // two event types the lens folds are sent, narrowed to `seq > afterSeq`
+    // so polling is a small delta, with the same recent-window cap the
+    // client accumulator applies.
+    'changes.ops': async (payload) => {
+      const sessionId = requireString(payload, 'sessionId')
+      const rawAfter = (payload as { afterSeq?: unknown } | null)?.afterSeq
+      if (rawAfter !== undefined
+        && (typeof rawAfter !== 'number' || !Number.isSafeInteger(rawAfter) || rawAfter < 0)) {
+        throw new SidebarError('bad-request', 'afterSeq must be a non-negative integer')
+      }
+      // An absent cursor means "from the very first event" — a session whose
+      // log opens on a tool event (subagent seeds do) carries seq 0, which a
+      // literal `> 0` comparison would drop, so the absent case floors at -1.
+      const afterSeq = rawAfter ?? -1
+      let events: readonly SidebarSessionEvent[] | undefined = ctx.sessions.get(sessionId)?.events
+      if (events === undefined) {
+        const persistence = ctx.get('sessionPersistence')
+        if (persistence !== undefined) {
+          try {
+            events = (await persistence.inspect(sessionId)).events
+          } catch {
+            // Cold read unavailable (session never persisted): an empty
+            // window is the honest answer, not a wire error.
+          }
+        }
+      }
+      if (events === undefined) return { events: [], lastSeq: Math.max(afterSeq, 0) }
+      const CHANGES_EVENTS_CAP = 4000
+      const filtered = events.filter(
+        event => (event.type === 'tool/call' || event.type === 'tool/result') && event.seq > afterSeq,
+      )
+      const window = filtered.length > CHANGES_EVENTS_CAP ? filtered.slice(filtered.length - CHANGES_EVENTS_CAP) : filtered
+      return { events: window, lastSeq: window.at(-1)?.seq ?? afterSeq }
+    },
     // Release a terminal immediately. The WebSocket close frame already does
     // this while the socket is open; this route covers the tab-close that
     // happens while the socket is down (reconnect loop), so a closed tab can