Merge the concurrent selector adaptation; ui-model stays the model owner

The remote side re-merged master (i18n workflow round) and restored the
pre-architecture ModelSelector package with the Session-side state
machine. Reconciliation keeps that merge's master content and reasserts
this branch's model architecture: business state lives in ui-model's
shared per-session directory (ctx.models), not on Session/
ConversationSnapshot; the input.model seat entry and the /model popup
stay the two same-source entries; the history modelTarget piggyback stays
removed. The ui-model-selector package, its roster row, and its allowlist
entry go; the smoke-real roster names ui-model.

packages/client/runtime/README.i18n.yaml

@@ -1,6 +1,6 @@
 # Bilingual-pair consistency record (docs/i18n/README.md): the git blob hash of each
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
-#   pnpm run verify-translation-pairing --write
-README.md: 4724ebc75d441252245a0e811a4ae34f8b529a98
-README.zh.md: 6a0076742efccaf946910c77c77a9b74194b9dc5
+#   pnpm run verify-translation-pairing --write packages/client/runtime/README.md
+README.md: 91c5487f9dbd6e04ff70ea560f87a89862cf37fe
+README.zh.md: 932fcb1a05fbf54a51b045559b351db0525eef1c

packages/client/runtime/README.md

@@ -22,13 +22,17 @@ SlotsService gives the renderer separate bare observables for `useSessions` and
 
 `SessionManager` retains the latest validated `session/title` control snapshot independently of list and session-instance arrival. Newer event seqs replace older snapshots, title timestamps contribute to list recency, and a subscription baseline discards any retained title beyond its `lastSeq` before the optional folded title arrives. Explicit session removal also clears the retained title. The client-facing `SessionSummary.title` is therefore only the actual durable title; `displayTitle` is always present and falls back through the cwd basename and session id. A cold persisted session keeps that fallback until opening or resuming it causes the host to fold and project its log-backed title.
 
+## Session model selection
+
+Each resident `Session` owns a `modelSelection` snapshot containing the current provider/model target, provider-grouped directory, provider-local failures, and the `idle`/`loading`/`ready`/`selecting`/`error` state. History establishes or refreshes the current target, opening a selector refreshes the directory, and selection failures preserve the last target and usable groups. Directory and selection operations share a monotonically increasing generation so an older response cannot overwrite a newer selection. A reconnect rebuild restores the target reported by the Host without replacing unchanged selection substructure.
+
 ## Model Experience
 
-None, as the client runtime hosts browser-side services and the session object layer; nothing here reaches a model request.
+None, as the session object layer selects the provider/model route used by a later Host request but adds no model-visible content.
 
 #### KV Cache effect
 
-None; this package neither assembles nor sends a provider request.
+Changing the target can change or invalidate provider-side cache reuse; this package does not alter the prompt prefix itself.
 
 ## Known Limitations and Deferred Work
 

packages/client/runtime/README.zh.md

@@ -22,13 +22,17 @@ SlotsService 分别为 renderer 提供 `useSessions` 与 `useWorkspaces` 的裸
 
 `SessionManager` 独立于列表和 Session 实例到达情况，保留最近一次通过验证的 `session/title` 控制快照。seq 更新的事件会替换旧快照，标题时间戳计入列表新近程度；订阅基线会先丢弃 seq 超过其 `lastSeq` 的任何已保留标题，再接收可选的折叠标题。显式移除 Session 也会清除已保留标题。因此，面向客户端的 `SessionSummary.title` 只包含真实的持久标题；`displayTitle` 始终存在，并依次回退到 cwd basename 和 Session id。冷启动的持久会话会保持该回退值，直到打开或恢复会话，促使主机折叠并投影日志支持的标题。
 
+## 会话模型选择
+
+每个常驻 `Session` 都拥有一个 `modelSelection` 快照，其中包含当前提供方/模型目标、按提供方分组的目录、逐提供方失败记录，以及 `idle`／`loading`／`ready`／`selecting`／`error` 状态。历史记录会建立或刷新当前目标，打开选择器会刷新目录；选择失败会保留上一个目标和可用分组。目录与选择操作共用单调递增的代次，因此较旧响应无法覆盖较新的选择。重连重建会恢复 Host 报告的目标，同时不替换未变化的选择子结构。
+
 ## 模型体验
 
-无。客户端运行时承载浏览器侧服务与 Session 对象层；这里没有任何内容进入模型请求。
+无，因为 Session 对象层会选择后续 Host 请求使用的提供方/模型路由，但不添加任何模型可见内容。
 
 #### KV Cache 影响
 
-无；该包既不组装也不发送提供方请求。
+更改目标可能改变提供方侧的缓存复用，或使其失效；该包本身不会改变提示词前缀。
 
 ## 已知限制与暂缓事项