fix(preset): keep the token meter host-plane and name unjoined agents

Moving the agent plane behind presets left two readers on the wrong side of
the host/agent line.

`dsh-token-meter` was disabled on the host and mounted inside each preset's
`compaction` realm, but its three projection units register into the
process-wide `sessionProjections` table. A unit registered from one preset
answers for every session, so whether a `minimal` session showed a context
meter depended on whether some other session had mounted `standard` since
boot, and a process that only ever ran `minimal` showed none. The meter takes
no configuration, keys every fold by Session, and registers no tool or prompt
section, so it returns to the host composition and leaves the presets'
`isolate` map; the realm and `compact-basic` stay, because what a preset
chooses is whether its agent compacts, not whether its tokens are counted.

Nothing named an agent that joined no preset. The join is a scope-parent link,
and without it the tools, prompt-section, and skill views resolve the empty
global layer: the agent publishes, the turn runs, and the model receives
nothing. `AgentPresets` now logs one warning per such agent while a roster is
configured, and the invariant companion fails outright — at
`system-prompt/assemble` rather than at publication, because an unjoined agent
is legal until it addresses a model and `recompose` binds exactly such an
agent. The warning stays advisory: a synchronous `agent/created` throw vetoes
publication, and the ACP bridge, SDK server, and headless bundle all create an
unjoined agent today.

Three limits are recorded rather than fixed: projection key presence is not a
per-session capability signal, a superseded standing generation is never
reclaimed, and a `cordis_mount` temporary plugin belongs to the composition
rather than the session that mounted it.

Fixes #2203

packages/self-modification/tool-cordis/README.zh.md

@@ -87,3 +87,4 @@ Namespace 插件：命名导出 `name`／`inject`／`Config`／`apply`，无默
 - **沙箱只用于约束诚实代码，并非安全边界**：可以访问沙箱全局变量上的 host realm helper，因此挂载代码可以触达 Node；加载该插件时，应当像授予 bash 工具一样慎重（见 § 信任立场）。
 - **`ctx` façade 不公开 `effect()`**：挂载代码无法注册定制 disposer；`on`／`provide`／`tools.register` 是受支持的清理路径。
 - **`vmTimeoutMs` 只限制同步求值**：async 挂载主体可逃出该边界；挂载代码没有 async 预算。
+- **临时 Plugin 属于组装，而不属于挂载它的那个会话**：group fiber 与 `dyn-N` 表是本行自己的，因此本行覆盖的每个 agent 共享它们——注册在某个 agent preset 的常驻挂载里时，一个会话挂载出来的东西会出现在另一个会话的工具目录和 `cordis_inspect what:"temporary"` 里，同一个 id 的第二次挂载会顶掉第一次。这与本包最初作为宿主平面行的语义一致（每进程一份）；只有当多个会话并发运行同一 preset 时才变得可观察。要做到逐会话，需要把 group 与表按调用方 agent 建键。