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per-session capability signal, a superseded standing generation is never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/src/api-catalog.ts

@@ -1212,7 +1212,7 @@ export const SERVICE_API: readonly ServiceApiEntry[] = [
     methods: [
       {
         signature: 'presentAs(mode: ToolPresentationMode): () => void',
-        jsDoc: '/**\n * Present this agent\'s tools in `mode` instead of the deployment default.\n *\n * Scoped only, and one declaration per agent: this is how an agent preset\n * composes a Code Mode agent beside native ones in the same process, and a\n * process-global override would be the `mode` config field instead.\n * @param mode - the presentation this agent\'s model sees.\n * @returns the exact disposer that restores the deployment default.\n */',
+        jsDoc: '/**\n * Present the calling scope\'s tools in `mode` instead of the deployment\n * default. Nearest scope on the chain wins, so a preset\'s standing\n * declaration covers every agent joined under it.\n *\n * Scoped only, and one declaration per scope: this is how an agent preset\n * composes Code Mode agents beside native ones in the same process, and a\n * process-global override would be the `mode` config field instead.\n * @param mode - the presentation the covered agents\' models see.\n * @returns the exact disposer that restores the deployment default.\n */',
       },
       {
         signature: 'register(definition: ToolDefinition): () => void',