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/settings.schema.ts

@@ -0,0 +1,53 @@
+/**
+ * settings domain zod schemas (names derived from map keys: settingsDescribeRequestSchema /
+ * settingsDescribeValueSchema / settingsUpdate* / settingsReplace*).
+ */
+
+import { z } from 'zod'
+import type { RequestPayload, ResponseValue } from './rpc-map.ts'
+import type { Wire } from './rpc.schema.ts'
+import type { SettingsNamespaceView, SettingsSecretView } from './settings.ts'
+
+/** One redacted secret slot. */
+export const settingsSecretViewSchema = z.object({
+  path: z.array(z.string()),
+  set: z.boolean(),
+}) satisfies z.ZodType<Wire<SettingsSecretView>>
+
+/** SettingsNamespaceView row of settings.describe and the write responses. */
+export const settingsNamespaceViewSchema = z.object({
+  ns: z.string().min(1),
+  schema: z.unknown(),
+  value: z.unknown(),
+  base: z.unknown().optional(),
+  user: z.unknown().optional(),
+  applies: z.union([z.literal('live'), z.literal('restart')]),
+  secrets: z.array(settingsSecretViewSchema),
+}) satisfies z.ZodType<Wire<SettingsNamespaceView>>
+
+/** settings.describe request payload. */
+export const settingsDescribeRequestSchema = z.object({}) satisfies z.ZodType<Wire<RequestPayload<'settings.describe'>>>
+
+/** settings.describe response value. */
+export const settingsDescribeValueSchema = z.object({
+  writable: z.boolean(),
+  namespaces: z.array(settingsNamespaceViewSchema),
+}) satisfies z.ZodType<Wire<ResponseValue<'settings.describe'>>>
+
+/** settings.update request payload. */
+export const settingsUpdateRequestSchema = z.object({
+  ns: z.string().min(1),
+  patch: z.record(z.string(), z.unknown()),
+}) satisfies z.ZodType<Wire<RequestPayload<'settings.update'>>>
+
+/** settings.update response value: the namespace's new redacted view. */
+export const settingsUpdateValueSchema = settingsNamespaceViewSchema satisfies z.ZodType<Wire<ResponseValue<'settings.update'>>>
+
+/** settings.replace request payload. */
+export const settingsReplaceRequestSchema = z.object({
+  ns: z.string().min(1),
+  section: z.record(z.string(), z.unknown()),
+}) satisfies z.ZodType<Wire<RequestPayload<'settings.replace'>>>
+
+/** settings.replace response value. */
+export const settingsReplaceValueSchema = settingsNamespaceViewSchema satisfies z.ZodType<Wire<ResponseValue<'settings.replace'>>>