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/fetch/handler.ts

@@ -43,6 +43,13 @@ import {
   goalCompleteRequestSchema,
   goalClearRequestSchema,
 } from '../api/goals.schema.ts'
+import {
+  settingsDescribeRequestSchema, settingsReplaceRequestSchema, settingsUpdateRequestSchema,
+} from '../api/settings.schema.ts'
+import {
+  credentialsDescribeRequestSchema, credentialsSetRequestSchema, credentialsUnsetRequestSchema,
+} from '../api/credentials.schema.ts'
+import { llmModelsRequestSchema, llmProvidersRequestSchema } from '../api/llm.schema.ts'
 
 /**
  * Unary dispatch table, keyed by (and compiler-locked to) RpcMethodMap: a map row without a
@@ -85,6 +92,14 @@ const UNARY_ROUTES: UnaryRoutes = {
   'goal.resume': { schema: goalResumeRequestSchema, invoke: (api, r) => api.goals.resume(r) },
   'goal.complete': { schema: goalCompleteRequestSchema, invoke: (api, r) => api.goals.complete(r) },
   'goal.clear': { schema: goalClearRequestSchema, invoke: (api, r) => api.goals.clear(r) },
+  'settings.describe': { schema: settingsDescribeRequestSchema, invoke: (api, r) => api.settings.describe(r) },
+  'settings.update': { schema: settingsUpdateRequestSchema, invoke: (api, r) => api.settings.update(r) },
+  'settings.replace': { schema: settingsReplaceRequestSchema, invoke: (api, r) => api.settings.replace(r) },
+  'credentials.describe': { schema: credentialsDescribeRequestSchema, invoke: (api, r) => api.credentials.describe(r) },
+  'credentials.set': { schema: credentialsSetRequestSchema, invoke: (api, r) => api.credentials.set(r) },
+  'credentials.unset': { schema: credentialsUnsetRequestSchema, invoke: (api, r) => api.credentials.unset(r) },
+  'llm.providers': { schema: llmProvidersRequestSchema, invoke: (api, r) => api.llm.providers(r) },
+  'llm.models': { schema: llmModelsRequestSchema, invoke: (api, r) => api.llm.models(r) },
 }
 
 /** Route lookup that narrows an arbitrary path segment to a map key (single cast point for the string→key refinement). */