docs(web): the composer bar is one session-maybe slot, not a swapped pair

fix(web): keep one composer bar DOM across the no-workspace transition

The composer.bar slot moves from session to session-maybe scope: with no
current session the entry still mounts, the machine faces (keyboard, stop,
command) arrive undefined, and the bar renders its normal DOM inert via the
disabled owner prop. DisabledInputBar and its parallel tree are gone, so the
textarea node survives the cold-start workspace pick instead of flashing
through a remount. A blank session whose workspace was deleted takes the
same inert path through owner props.

test(web): add the composer DOM-continuity acceptance probe

Drives a real dsh web server with headless chromium through the cold-start
-> pick-workspace -> type flow and asserts the composer textarea is the
same DOM node throughout (a marker property must survive). Rerun
prerequisites are in the header comment.

docs(web): session-maybe identity is adoption, not hold-forever

fix(web): session-maybe entries adopt the first session, then remount like strict entries

A session-maybe entry used to keep one React instance across every
transition, so component-local state leaked between sessions once the
composer bar moved to that scope (PermissionSelect's optimistic pick, the
IME composition guard). Identity is now adoption: an incarnation born
session-less holds through the arrival of the first session (the blank
shell's DOM survives the workspace pick), and afterwards behaves exactly
like a strict session entry — a switch or a drop to no-session remounts,
clearing local state by construction. The child key is an incarnation
counter kept in the stable outlet wrapper via render-phase setState.

chore: knip knows the root acceptance probe's playwright dependency

scripts/hero-composer-dom-continuity.mjs resolves playwright through
apps/web's devDependency tree (createRequire), which knip cannot follow;
ignore it at the root workspace.

packages/client/ui-conversation/README.zh.md

@@ -20,7 +20,7 @@ todo 两个面就是在该形状上的两个注册项，都是普通注册方插
 
 逐 Session UI 状态中的选择与活跃视图位于已声明的聊天 store（`stores.ts` `createChatStore`）中；InputHub 拥有输入区状态机，并将草稿镜像到该 store 以便持久化。apply 将同一个 store handle 传给严格限定于会话的子树、聊天视图和详情注册，因此每个会话内共享一个实例，框架拥有其生命周期。组件保持纯粹：框架标准工具包提供 `useSession`／`sessionId`、全局 `useSessions`／`useWorkspaces`，以及输入状态机的 `useInput`／`inputActions`；store 表层与 inject factory 提供其余状态和回调。
 
-输入栏为 `'conversation.input.plan'`（位于本地 access 模式控件右侧）和 `'conversation.input.model'`（渲染在 pending 指示器与发送／停止按钮之前）声明会话作用域的单实例 seat，并为 overlay、dock、left 和 right 输入扩展声明列表 slot。各功能包拥有相应控件及其状态；ui-conversation 提供放置位置、`locked` owner prop 和标准 slot share。当 `plan` 投影的有效目标为 plan mode 时，InputBar 将文本框 placeholder 切换为 plan 任务措辞，经本包注册的 `command.hint` locale 命名空间本地化，并与已认领 `/plan` 命令的提示逐字共用同一份文案（经标准套件 `useProjection` 读取的 host 折叠值；owner 提供的 placeholder 优先）。另一个会话视图活跃时，待处理的 composer 接管仍保持挂载，使被阻塞的 agent（智能体）仍能收到回答；没有待处理交互时，活跃会话的 composer 归 Chat 所有。常驻无会话壳使用 `DisabledInputBar`，因此不会分发任何会话作用域的控件 seat。
+输入栏为 `'conversation.input.plan'`（位于本地 access 模式控件右侧）和 `'conversation.input.model'`（渲染在 pending 指示器与发送／停止按钮之前）声明会话作用域的单实例 seat，并为 overlay、dock、left 和 right 输入扩展声明列表 slot。各功能包拥有相应控件及其状态；ui-conversation 提供放置位置、`locked` owner prop 和标准 slot share。当 `plan` 投影的有效目标为 plan mode 时，InputBar 将文本框 placeholder 切换为 plan 任务措辞，经本包注册的 `command.hint` locale 命名空间本地化，并与已认领 `/plan` 命令的提示逐字共用同一份文案（经标准套件 `useProjection` 读取的 host 折叠值；owner 提供的 placeholder 优先）。另一个会话视图活跃时，待处理的 composer 接管仍保持挂载，使被阻塞的 agent（智能体）仍能收到回答；没有待处理交互时，活跃会话的 composer 归 Chat 所有。composer bar 坑位本身为 `session-maybe`：没有当前会话时，同一个 bar 以惰性态渲染（machine face 缺席、`disabled` owner prop），而不是换入一棵平行的 disabled 树，因此 textarea DOM 在选定 workspace 的切换中得以存活；严格会话作用域的控件 seat 在会话存在之前保持为空。
 
 `src/client/` 按未来的包拆分组织：`contract/` 是唯一的跨领域共享表层（`slots.ts` slot 声明 + 组合后的 slot props，包括工具行契约、`views.ts` 共享原语、`tool-call-model.ts`）；`skeleton/`、`chat/` 和 `toolviews/`（示例注册方）领域目录只导入 contract 文件，彼此绝不导入；`apply.ts` 是唯一允许导入全部三个领域的组装点。`/client` 导出表层只包含契约：`apply`／`inject`、两个服务类和 `contract/` 类型家族；实现组件（骨架、聊天行）与 store factory 保持内部状态，只能通过 apply 的 slot 注册到达页面（测试通过 `./src/*` 子路径获取它们）。