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per-session capability signal, a superseded standing generation is never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/core/agent-tool-mode/src/index.ts

@@ -5,8 +5,10 @@
  * The tool registry itself stays on the host plane — the agent loop's
  * scheduler, the API proxy's presenters, and every tool plugin are all its
  * consumers, so it cannot move into a preset. What a preset CAN own is the
- * presentation: `ctx.tools.presentAs()` declares it for the mounting agent
- * alone, so a Code Mode agent runs beside native ones in one process.
+ * presentation: `ctx.tools.presentAs()` declares it for the mounting SCOPE,
+ * which is the preset's standing mount, so the declaration covers every agent
+ * joined to that preset and a Code Mode preset runs beside native ones in one
+ * process. One row per composition, not one per session.
  *
  * A code mode needs a TypeScript code runtime, which is a host-plane service
  * ([`dsh-code-runtime-worker`](../../code-runtime/code-runtime-worker/README.md)).
@@ -50,8 +52,8 @@ export const Config: z<Config> = z.object({
 })
 
 /**
- * Declare this agent's tool presentation.
- * @param ctx - the mounting agent's scope context.
+ * Declare the tool presentation for every agent this composition covers.
+ * @param ctx - the mounting composition's scope context (a preset's standing scope).
  * @param config - the selected presentation.
  */
 export function apply(ctx: Context, config: Config): void {