fix(sidechat): read the transcript through the plugin's own events route

DSH 0.1.2-alpha.1 removed the client `ctx.connection.api` face (Remote
gateway migration), so every Side Chat transcript poll (`sessions.history`)
threw TypeError into the view's catch and was swallowed — the tab rendered
an empty transcript forever, silently (no console error, so the mount lane
never caught it). The successor APIs are not a drop-in either:
session/follow|page reject plain session addresses for origin:'subagent'
logs (agent-busy fence) and paging cannot read past the current cursor.

Move the transcript to the plugin's own wire — one transport for every
DSH generation:

- new `sidechat.events` route: live threads read the in-memory
  `agent.session.events`; cold threads read `sessionPersistence.inspect`
  (both seams exist since 0.1.0-rc.8; alpha.1's inspect returns the
  expanded logical log, never the packed chunk-row encoding). The
  inherited seed is cut host-side (`threadOwnLogEvents`), polls ride an
  `afterSeq` delta, and the response is tail-capped at 8000 events (the
  old client walk ceiling).
- SideChatView.fetchThread is single-path; collectOwnEvents (the client
  walk) is gone, and so are the ctx.connection mirror and inject entry
  (no consumer left).
- transcriptRows keeps re-cutting at session/end-seed as defense in
  depth.

Verification:
- unit: sidechat.events route (seed cut, afterSeq delta + never
  resurrecting the seed, cap, cold/live sources, 404/503/bad-request),
  full suite 1104 passed; typecheck and build (purity gate) green.
- mount e2e vs a real dsh-v0.1.2-alpha.1 source build: 14/14, including
  the Side Chat tab sweep polling sidechat.events (performance resource
  assertion) and live + post-dispose (persisted) route reads.
- mount e2e vs PATH dsh 0.1.0-rc.8: 14/14 (no regression).

docs/plans/2026-08-20-sidechat-tab-design.md

@@ -95,3 +95,4 @@
   2. 图标语义：线程切换菜单改自绘 `IconHistoryOutline16`（逆时针时钟）、保存按钮改自绘 `IconSaveOutline16`（软盘），沿用 1.5px 描边规范（primitives 无现成 history/save 图标）。
   3. 重开线程 Tab 丢工具行：根因**不在宿主**（`session.history` cold 路径原样返回 `tool/call`，见 `api-proxy.ts:749` 与 `chunk-rows.ts` 的无损 chunk 压缩）而在首挂回源窗口——旧实现 8 事件/页 × 32 页 = 256 事件上限，而 cold 读会把 chunk-rows 展开回每个流式 delta 一条事件，一轮回答动辄数百事件，较早的 `tool/call` 掉出窗口（settled 文本靠最终 `assistant/message` 幸存）。修复 = 抽出 `collectOwnEvents`（200 事件/页 × 40 页帽、日志穷尽/无标记时落定 `seedBoundary:0` 停止每轮重走），单测覆盖四分支。
   4. Subagent 页「目录损坏」行：见 §5 修正——种子追加 descriptor + SubagentView/subagent-detect 按前缀过滤（`isSideThreadSummary` 同时修好 autoOpenSubagent 误触发与计数膨胀）。旧版创建的线程仍是 corrupt 诊断行，由 SubagentView 的标题前缀过滤兜底隐藏。
+- **转录传输迁至自有路由（DSH 0.1.2-alpha.1 适配）**：§6 原设计的时间线轮询走通用 `connection.api.sessions.history` RPC——该客户端面（`ctx.connection.api`）在 0.1.2-alpha.1 的 Remote-gateway 迁移中被整体移除，且其继任者（`session/follow`/`session/page`）对 `origin:'subagent'` 会话强制 subagent 地址寻址（普通 `{kind:'session'}` 地址被 `agent-busy` 拒绝），纯分页也拿不到最新尾页（`throughSeq` 不得超当前游标）。修复 = 新增 **`sidechat.events`** 路由（`src/sidechat-routes.ts`）：host 侧读线程日志（live 走 `agent.session.events`，冷线程走 `ctx.get('sessionPersistence').inspect`——两版 DSH 同形，alpha.1 的 inspect 返回展开后的逻辑日志而非磁盘上的打包 chunk-row），服务端切 `session/end-seed`（`threadOwnLogEvents`，`collectOwnEvents` 的 walk 语义下沉），`afterSeq` 增量 + 8000 事件尾部帽（对齐旧 walk 上限 40×200）。客户端 `fetchThread` 单路径化，删除 `collectOwnEvents` 与 `ctx.connection` 镜像/inject。种子切割仍由 `transcriptRows` 客户端二次防御。挂载冒烟补 live+冷读两条断言。