feat(apiproxy): settings/credentials/llm wire domains, frames, and write guard

Eight compiler-locked methods: settings.describe/update/replace serve
redacted layered namespace views (secrets structurally absent from every
layer, write-only in the update direction) and fold seam refusals into
settings-rejected; credentials.describe/set/unset expose value-free views
with credential-rejected on shadowed writes; llm.providers merges the
configurable directory with live routes and llm.models claims the
host-scoped catalog reservation through the buildModelCatalog extraction
session.models now shares. Three HostFrame invalidations bridge the seam
events (host/settings-changed, host/credentials-changed,
host/models-changed), and the connection route generalizes the native-
dialog check into a privileged-method set covering all four writes. The
fixture and both fake clients grow the same face.

packages/host/apiproxy/src/api/index.ts

@@ -11,6 +11,9 @@ import type { CommandsApi } from './commands.ts'
 import type { SkillsApi } from './skills.ts'
 import type { EventsApi } from './events.ts'
 import type { GoalsApi } from './goals.ts'
+import type { SettingsApi } from './settings.ts'
+import type { CredentialsApi } from './credentials.ts'
+import type { LlmApi } from './llm.ts'
 import type { ClientResponse, RpcReceipt } from './rpc.ts'
 
 /** Root interface of the unified API surface. New client-request domain = one new file pair + one field here + one map row. */
@@ -22,6 +25,9 @@ export interface ApiProxy {
   skills: SkillsApi
   events: EventsApi
   goals: GoalsApi
+  settings: SettingsApi
+  credentials: CredentialsApi
+  llm: LlmApi
   /** Response entry for server-requests (client-response, echoing their rpcId); not a domain method (four-quadrant model). */
   respond(message: ClientResponse): Promise<RpcReceipt>
 }
@@ -37,6 +43,9 @@ export type { CommandsApi, CommandDescriptor } from './commands.ts'
 export type { SkillsApi, SkillEntry } from './skills.ts'
 export type { EventsApi, MuxFrame, HostFrame, ToolCallView, ToolEventView, ToolResultView } from './events.ts'
 export type { GoalsApi, GoalId, GoalRef } from './goals.ts'
+export type { SettingsApi, SettingsNamespaceView, SettingsSecretView } from './settings.ts'
+export type { CredentialsApi, CredentialView } from './credentials.ts'
+export type { ConfigurableProviderView, LlmApi } from './llm.ts'
 export type { ApprovalResponsePayload } from './approvals.ts'
 export type { QuestionResponsePayload } from './questions.ts'