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per-session capability signal, a superseded standing generation is never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

@@ -252,6 +252,12 @@ export function apply(ctx: Context, config: AcpConfig): void {
         assertOpen()
         validateSessionParams(params)
         const sessionId = SessionId(randomUUID())
+        // No preset composition: the ACP bundle keeps the model-facing rows in
+        // the host plane, so this agent reads them from the global registry
+        // layer. A deployment that configures `dsh-agent-presets` has to join
+        // one here first — registration visibility inherits only along the
+        // `dsh-scope` parent chain, and an agent created without that link
+        // reads an empty global layer and reaches the model with no tools.
         const handle = await agents.create({
           sessionId,
           meta: { cwd: params.cwd },