fix(apiproxy): serve history events and projections from one log position

Review found two defects in the previous commit's ordering fix.

@pku-xht: `historyStateFor` copied the attached session's events, the handler
then awaited `presenterScopeFor`, and only then read the projection baseline
off the still-live Session. An append during that await served events cut at N
beside a baseline folded to N+1 — one response describing two moments. The
same restructure had also moved the baseline read outside the `try`, so a
failing snapshot escaped the structured `internal` error.

Both awaits now happen before the cut: `historySourceFor` resolves which
session serves the read, `presenterScopeFor` ensures the recorded composition,
and `historyCutOf` then reads events and baseline adjacently with nothing
between them. The whole sequence is back inside the try.

The invariant judged any scoped assembly with a chain of one as an unjoined
agent, which rejects a legitimate assembly in a standing preset key (that key
has no parent of its own). It now gates on `context.agent` — a scope-only read
is not an agent and is out of range by construction rather than by a premise
about who else calls `assemble` — and asks the roster's own
`composedPreset()` instead of introspecting chain length. The advisory warning
uses the same relation.

Also from review: the `2026-08-05-per-agent-tool-presentation` note still
described `presentAs` as per-agent, which standing mounts made false and this
branch's own rewording contradicts; the duplicated "process-wide unit table"
argument collapses to the Agent Note with pointers from the five copies; a
dead `.sort()` before `arrayContaining`; and change-history narration in the
tool-cordis README.

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

@@ -87,4 +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。
+- **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。多个会话并发运行同一 preset 时这一点才变得可观察。要做到逐会话，需要把 group 与表按调用方 agent 建键。