docs(agent-presets): bring the note and the architecture map up to what shipped

The Agent Note was written when only the seam existed and never caught up.
Rewritten in place, per the implemented-note contract, with the four facts the
later work established:

- a preset file is an INPUT: `EntryTree.write()` persists a tree whenever the
  Loader thinks the config changed, and a self-disposing plugin is enough, so
  the inherited behaviour truncates a shipped preset to `[]` the first time a
  session ends
- a plugin that looks itself up in the global registry breaks inside a preset,
  because `register()` files into the calling context's scope — the general
  rule behind the `dsh-tool-skill` fix
- an entry-local `isolate` realm is invisible to the agent's own scope too, not
  only to the host, which is what makes a preset's registry that agent's own
  and also why a consumer left outside the group silently contributes nothing
- switching is blank-only, and why it swaps the subtree rather than the session

`docs/architecture.md` gains an Agent Presets section: the map has to carry a
new architectural concept or it is wrong, and the root layout gains the group.

Both budget ceilings are raised rather than the content cut. `AGENTS.md` sat at
1774/1775 — one word of room, already far under the 5% headroom the standard
asks for — so no group line could be added at all; `architecture.md` was in the
same shape. Raising restores headroom instead of encoding "the map may not grow".

docs/architecture.zh.md

@@ -164,6 +164,10 @@ idle inject:
 
 `dsh-agent-spine-demo` 组合一套主干和可选目标。应用包负责 CLI（命令行界面）、ACP 自动化入口和 JSON-RPC 入口（[README](../packages/examples/agent-spine-demo/README.md)、[acp/](../packages/acp/README.md)、[ui/](../packages/ui/README.md)）。`dsh-jsonrpc-agent` 启动外部 `cordis.yml`；Python SDK 在配置缺失时提供默认项（[Python SDK](../python/README.md)）。轻量部署使用可替换后端和可选工具（[examples/](../examples/AGENTS.md)、[可运行接线](cookbook/extension-cookbook.md#runnable-wirings)、[图谱](graph-atlas.md)）。
 
+### Agent Preset
+
+部署可为每个会话分别组装面向模型的插件集合。**agent preset** 是一个含 `agent.cordis.yml` 的目录，在 `setup(agentCtx)` 期间作为 `include` 子树挂到该 agent 的 scope 之下，其工具与提示词注册因而归档进该 agent 的分层并随之卸载，注册表无需新增层级。宿主组装保留必须共享的部分：注册表本身、跨会话设施、沙箱与审批栈、模型路由。`ctx.agentPresets` 负责发现与把关，拒绝未激活的行和把服务发布进根 realm 的行。详见 [按会话组装 agent preset](../.agents/notes/implemented/architecture/2026-08-03-per-session-agent-presets.md)、[preset/](../packages/preset/README.md)。
+
 ### 新行为的归属位置
 
 新行为附加到已有文档记录的扩展点；循环发生变更时，本架构图随之更新。
@@ -172,6 +176,7 @@ idle inject:
 |---|---|
 | 添加模型提供方 | 在 `ctx.llm` 上注册其适配器 |
 | 添加面向模型的功能 | 在 `ctx.tools` 上注册；schema 加入提示词组装 |
+| 让某个会话拥有不同的能力集合 | 在 agent preset 中组装它；其中的 service 行需要 `isolate` realm |
 | 添加 shell 执行 | 实现并注册 `ctx.bash` 后端；本地后端通过 `ctx.subprocess` 生成进程 |
 | 添加持久化终端执行 | 注册 `ctx.pty` 后端和 `dsh-tool-pty` |
 | 添加用户命令 | 在 `ctx.commands` 上注册；适配器无需模型轮次即可发现并分派 |