fix(web-config): close the wire boundary, the redacted-replace data loss, and three P2s

Five findings from the #939 review, each reproduced before being fixed.

**Configuration reads are as privileged as writes.** `settings.describe`
returns every exposed namespace's configuration and `credentials.describe`
reports whether an arbitrary environment-variable name is configured and from
where — reconnaissance no anonymous caller should have. Both join
PRIVILEGED_METHODS, so the whole configuration plane is loopback-only until
real authentication exists; `trustedHosts` was never authentication. The model
catalog stays reachable: it carries no endpoints or key state, and a LAN
client's model picker legitimately needs it. Asserted over a real HTTP server,
because the Host header a browser actually sends is what decides this.

**The proxy serves only namespaces a registered model provider addresses.**
The settings seam is general — any plugin may register one — but the Web
configuration plane is the model-provider surface. Without the gate, every
future `settings.register()` would silently become remotely readable and
writable configuration. An unregistered namespace and an unexposed one answer
identically, so no caller can enumerate the registry one probe at a time.

**Path-addressed writes replace the redacted-document rebuild.** The editor
reads the REDACTED descriptor, so rebuilding a section from it and replacing
wholesale deleted every literal secret the wire never returned — reproduced as
`{baseURL, reasoning}` in, stored `apiKey` gone out. `settings.mutate` applies
set/unset ops to the section as it stands at the front of the seam's write
queue, and the client names only fields it can see, so an unseen secret is
untouched by construction rather than by care.

P2s in the same pass: `llm/adapters-updated` now contains async listener
rejections (an uncontained one escaped as unhandledRejection, contradicting
the documented "observer failures are contained"); llm-deepseek's retry-policy
swap uses the atomic `registration.replace` instead of dispose-then-register,
which published `[]` then `["deepseek-official"]` so an observer saw the
provider disappear and come back; and a transport rejection no longer strands
the page in `loading` or a card in `busy`, with removal failures surfaced on
the page banner instead of swallowed.

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

@@ -43,7 +43,7 @@ export type { CommandsApi, CommandDescriptor } from './commands.ts'
 export type { SkillsApi, SkillEntry } from './skills.ts'
 export type { EventsApi, MuxFrame, HostFrame, QueuedInboxItem, ToolCallView, ToolEventView, ToolResultView } from './events.ts'
 export type { GoalsApi, GoalId, GoalRef } from './goals.ts'
-export type { SettingsApi, SettingsNamespaceView, SettingsSecretView } from './settings.ts'
+export type { SettingsApi, SettingsNamespaceView, SettingsPathOpView, SettingsSecretView } from './settings.ts'
 export type { CredentialsApi, CredentialView } from './credentials.ts'
 export type { ConfigurableProviderView, LlmApi } from './llm.ts'
 export type { ApprovalResponsePayload } from './approvals.ts'

packages/host/apiproxy/src/api/rpc-map.ts

@@ -52,6 +52,7 @@ export interface RpcMethodMap {
   'settings.describe': SettingsApi['describe']
   'settings.update': SettingsApi['update']
   'settings.replace': SettingsApi['replace']
+  'settings.mutate': SettingsApi['mutate']
   'credentials.describe': CredentialsApi['describe']
   'credentials.set': CredentialsApi['set']
   'credentials.unset': CredentialsApi['unset']

packages/host/apiproxy/src/api/rpc.schema.ts

@@ -51,6 +51,7 @@ export const rpcErrorSchema: z.ZodType<RpcError> = z.discriminatedUnion('code',
   z.object({ code: z.literal('command-error'), message: z.string(), details: z.object({}) }),
   z.object({ code: z.literal('unknown-command'), message: z.string(), details: z.object({}) }),
   z.object({ code: z.literal('settings-rejected'), message: z.string(), details: z.object({ ns: z.string() }) }),
+  z.object({ code: z.literal('settings-not-exposed'), message: z.string(), details: z.object({ ns: z.string() }) }),
   z.object({ code: z.literal('credential-rejected'), message: z.string(), details: z.object({ ref: z.string() }) }),
   z.object({ code: z.literal('title-invalid'), message: z.string(), details: z.object({ sessionId: z.string() }) }),
   z.object({ code: z.literal('internal'), message: z.string(), details: z.object({}) }),

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

@@ -55,6 +55,12 @@ export interface RpcErrorDetailsMap {
    * read-only provider, or storage failure); the message is the seam's text.
    */
   'settings-rejected': { ns: string }
+  /**
+   * A settings namespace exists in the seam but is outside the configuration
+   * plane's model-provider boundary, so this proxy neither reads nor writes
+   * it; the message names the namespace.
+   */
+  'settings-not-exposed': { ns: string }
   /** A credential write was refused (read-only shadowing layer or storage failure); the message is the seam's own text. */
   'credential-rejected': { ref: string }
   'title-invalid': { sessionId: SessionId }

packages/host/apiproxy/src/api/settings.schema.ts

@@ -6,7 +6,7 @@
 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'
+import type { SettingsNamespaceView, SettingsPathOpView, SettingsSecretView } from './settings.ts'
 
 /** One redacted secret slot. */
 export const settingsSecretViewSchema = z.object({
@@ -49,5 +49,20 @@ export const settingsReplaceRequestSchema = z.object({
   section: z.record(z.string(), z.unknown()),
 }) satisfies z.ZodType<Wire<RequestPayload<'settings.replace'>>>
 
+/** One path-addressed edit of settings.mutate. */
+export const settingsPathOpSchema = z.discriminatedUnion('op', [
+  z.object({ op: z.literal('set'), path: z.array(z.string()), value: z.unknown() }),
+  z.object({ op: z.literal('unset'), path: z.array(z.string()) }),
+]) as unknown as z.ZodType<Wire<SettingsPathOpView>>
+
+/** settings.mutate request payload. */
+export const settingsMutateRequestSchema = z.object({
+  ns: z.string().min(1),
+  ops: z.array(settingsPathOpSchema),
+}) satisfies z.ZodType<Wire<RequestPayload<'settings.mutate'>>>
+
+/** settings.mutate response value: the namespace's new redacted view. */
+export const settingsMutateValueSchema = settingsNamespaceViewSchema satisfies z.ZodType<Wire<ResponseValue<'settings.mutate'>>>
+
 /** settings.replace response value. */
 export const settingsReplaceValueSchema = settingsNamespaceViewSchema satisfies z.ZodType<Wire<ResponseValue<'settings.replace'>>>

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

@@ -34,6 +34,15 @@ export interface SettingsNamespaceView {
   secrets: SettingsSecretView[]
 }
 
+/**
+ * One path-addressed edit carried by `settings.mutate`. `set` writes the
+ * value at the path (creating intermediate objects); `unset` removes it. The
+ * empty path addresses the section root.
+ */
+export type SettingsPathOpView =
+  | { op: 'set'; path: string[]; value: unknown }
+  | { op: 'unset'; path: string[] }
+
 /** Settings-domain unary methods (the map keys settings.* of RpcMethodMap). */
 export interface SettingsApi {
   /**
@@ -60,4 +69,14 @@ export interface SettingsApi {
    * keep) or accept the reset.
    */
   replace(request: RpcRequest<{ ns: string; section: object }>): Promise<RpcResponse<SettingsNamespaceView>>
+
+  /**
+   * Apply path-addressed edits to one namespace's user section, resolved
+   * against the section as stored — NOT against whatever the caller last
+   * read. This is the removal path for any client holding the redacted
+   * descriptor: it names the field it means, so a secret the wire never
+   * returned cannot be deleted as a side effect. `replace` remains the
+   * deliberate wholesale reset.
+   */
+  mutate(request: RpcRequest<{ ns: string; ops: SettingsPathOpView[] }>): Promise<RpcResponse<SettingsNamespaceView>>
 }