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per-session capability signal, a superseded standing generation is never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/bundle/web-app/cordis.patch.yml

@@ -270,8 +270,17 @@
 - id: plan-mode
   disabled: true
 
-- id: token-meter
-  disabled: true
+# The token METER stays on the host plane; only the compaction backend that
+# reads it moves. It takes no configuration at all, keys every fold by Session,
+# and registers no tool or prompt section, so one host instance serves every
+# preset exactly as before. It also owns the `tokenUsage`/`contextPressure`/
+# `contextBreakdown` projection units, and the projection registry is
+# process-wide rather than scope-layered: registered from inside a preset, the
+# browser's context meter would appear for a session whose own composition
+# mounts no meter as soon as some OTHER session mounted one, and disappear
+# entirely in a process that only ever ran `minimal`. That is the same criterion
+# `tasks` and `goals` are read by — a Service the host and every preset can see
+# belongs to the plane both can see.
 
 - id: compact-basic
   disabled: true