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.md

@@ -87,4 +87,4 @@ Mounting or unmounting a prompt or tool contribution changes later request prefi
 - **The sandbox is containment for honest code, not a security boundary** — host-realm helpers on the sandbox global are reachable, so mount code can reach Node; load this plugin as deliberately as you would grant a bash tool (see § Trust stance).
 - **The `ctx` façade exposes no `effect()`** — mount code cannot register a bespoke disposer; `on`/`provide`/`tools.register` are the supported cleanup paths.
 - **`vmTimeoutMs` bounds only synchronous evaluation** — an async mount body escapes it; there is no async budget on mount code.
-- **Temporary Plugins belong to the composition, not to the session that mounted one** — the group fiber and the `dyn-N` table are this row's own, so every agent the row covers shares them: registered inside an agent preset's standing mount, one session's mount is visible in another session's tool catalog and `cordis_inspect what:"temporary"`, and the second mount of an id replaces the first. That matched the host-plane row this package started as (one per process); it becomes observable once several sessions run the same preset concurrently. Per-session temporary plugins would need the group and table keyed by the calling agent.
+- **Temporary Plugins belong to the composition, not to the session that mounted one** — the group fiber and the `dyn-N` table are this row's own, so every agent the row covers shares them: registered inside an agent preset's standing mount, one session's mount is visible in another session's tool catalog and `cordis_inspect what:"temporary"`, and the second mount of an id replaces the first. Several sessions running one preset concurrently is where that becomes observable. Per-session temporary plugins would need the group and table keyed by the calling agent.