fix(web): correct the preset-layer contracts review found stale

None of these change behavior; each said something that was not true.

`SessionCwdConflict`'s doc block had been left stranded above the
`AgentPresetConflict` inserted under it, so one class carried a comment
about the other and the second carried none.

The roster comment named a `.system` directory that does not exist; the
shipped root is `config/agent-presets/`, and `system` is the trust its
entries carry.

The real-composition test attributed the disabled `api-gateway` row to
"side effects outside this process" alongside the port and the exporter.
It is disabled for a different reason — the api-proxy cannot mount in
this layer at all — and hiding that behind the same phrase would leave a
later layer unable to tell whether the line can come out.

One test claimed to refuse an adoption while asserting only that the
header records the preset; it now says what it checks.

`PERSONA_SECTION`/`PERSONA_ORDER` existed twice, once in the registry
that declares the slot and once restated in the row that replaces it —
a drift that would land a preset's persona beside the deployment's
instead of shadowing it. The registry exports them now.

The preset conflict message read "already runs agent preset undefined"
for a session that records none, which is the shape a deployment with no
roster produces; it names that case instead, with the regression that
reaches it through the gateway.

Finally, `PresetTree.write()` drops the `loader/config-update` the
inherited method emits — recorded on the override, since a future
edit-while-running flow needs its own persistence path.

packages/cordis/tool-cordis/src/api-catalog.ts

@@ -96,6 +96,10 @@ export const SERVICE_API: readonly ServiceApiEntry[] = [
         signature: 'async mount(agentCtx: Context, id?: string): Promise<AgentPreset>',
         jsDoc: '/**\n * Compose one agent from a preset, installing it under that agent alone.\n *\n * Call from the agent factory\'s `setup(agentCtx)`; a rejection there rolls\n * the agent creation back, so a broken preset never yields a half-composed\n * session.\n * @param agentCtx - the agent\'s scope context.\n * @param id - the preset id, or `undefined` for {@link defaultId}.\n * @returns the preset that was mounted, for the caller to record.\n * @throws when the preset is unknown or its composition is unusable.\n */',
       },
+      {
+        signature: 'serviceFor<K extends string & keyof Context>(agent: { ctx: Context }, name: K): Context[K] | undefined',
+        jsDoc: '/**\n * One agent\'s instance of a service its preset mounted.\n *\n * A preset publishes services behind `isolate` realms, which are invisible\n * outside the group that declares them — including to the host. This is how a\n * caller holding the agent reads one anyway: a request that is ABOUT a\n * session but arrives from outside it, which is every browser RPC.\n *\n * Read addressing only. A host row that `inject`s a service cannot use this,\n * because injection resolves before any session exists and has no agent to\n * key by; such a service belongs on the host plane instead.\n * @param agent - the agent whose composition to look inside.\n * @param name - the service name as the preset\'s rows resolve it.\n * @returns the agent\'s instance, or undefined when its preset mounts none.\n */',
+      },
     ],
   },
   {