fix(host): pin model discovery to loopback and drop its unread wire field

llm.discoverModels was reachable from any declared trusted host. The
method takes a caller-supplied baseURL and makes the host issue a GET to
it, then reports the status or the parsed body — so on a LAN deployment
an anonymous caller had a probe for whatever the host can reach and the
browser cannot, plus a path that carries a draft credential. The
PRIVILEGED_METHODS doc already states the rule this broke: trustedHosts
is a DNS-rebinding fence, not authentication, so the configuration plane
stays loopback-same-origin. It is in that set now, asserted both against
the hand-built fence and over real HTTP beside the catalog reads that
deliberately stay reachable.

supportsDiscovery and listModelDiscoveryNamespaces are gone. The field
was required on the wire and read by nobody: its own contract said a
surface should offer the action "instead of naming an adapter family it
would have to hardcode", while the surface hardcodes llm-pi-ai in two
places and gates the button on whether there is anything to probe. Its
shape did not fit the second caller either — the create card has no row
to read a per-row field from. Keeping a required field alive for a
consumer that may never arrive costs every producer and fixture a value
nobody consults, which is exactly how the fixtures drifted. The registry
that fed it had no other production consumer, so registration and
disposal are now observed through the offer itself.

The Agent Note claimed the key is never logged, which the wire schema
beside it already contradicts, and predated both the provider field and
the catalog-answer path. The two new public types pointed at core.md
without a type-equiv block or manifest entry, so the generated service
catalog named documentation that did not exist.

docs/core-data-structures/core.md

@@ -259,6 +259,55 @@ interface LlmModelInfo {
 }
 ```
 
+A provider a surface is still drafting has no route and no catalog, so interrogation is described separately: the request carries the draft the user is editing, and the reply is candidates a surface may adopt rather than a catalog it must serve.
+
+```ts type-equiv
+/**
+ * One interrogation of a provider endpoint that configuration has not stored
+ * yet. Configuration surfaces send the draft a user is still editing, so the
+ * request carries the endpoint and credential directly instead of naming a
+ * route: a provider being added has no route to name.
+ */
+interface LlmModelDiscoveryRequest {
+  /**
+   * Route the draft is editing, when it edits an existing one. A route whose
+   * adapter already knows its models answers from that knowledge instead of
+   * asking the endpoint — the adapter's own registry is the better answer, and
+   * it costs no network call.
+   */
+  provider?: string
+  /**
+   * Endpoint to interrogate. Optional because a route the adapter already
+   * describes needs none; a route it does not must supply one.
+   */
+  baseURL?: string
+  /** Wire protocol the endpoint speaks, when the draft names one. */
+  api?: string
+  /** Credential for this interrogation alone; the harness never stores it. */
+  apiKey?: string
+  /** Caller cancellation; implementations must settle promptly after it aborts. */
+  signal?: AbortSignal
+}
+```
+
+```ts type-equiv
+/**
+ * One model an endpoint reports about itself. Every field but the id is
+ * optional because most provider listings disclose an id and nothing else;
+ * a surface adopting one of these still owes the capacities its adapter needs.
+ */
+interface LlmDiscoveredModel {
+  /** Model id the endpoint accepts. */
+  id: string
+  /** Human-readable name when the endpoint supplies one. */
+  name?: string
+  /** Maximum combined request and response context, when disclosed. */
+  contextWindow?: number
+  /** Maximum output tokens, when disclosed. */
+  maxTokens?: number
+}
+```
+
 Correctness-sensitive metadata is resolved separately from the advisory catalog and is owned by the adapter serving the exact route. Context capacity, adapter call defaults, and reasoning choices share one exact-model result so consumers do not repeat authoritative model resolution.
 
 ```ts type-equiv