feat(web): expose the agent-preset roster over the API

`agentPreset.list` gives a browser the deployment's roster so it can offer a
choice when starting a session. Each row carries the id, its `trust`, and
whether it is the current default.

`trust` is on the wire deliberately: a `user` preset is exactly as privileged
as the plugins it names, so a surface that offers one alongside a shipped
preset can say which is which rather than presenting both as vetted.

The domain is read-only. A preset is a composition on disk, so authoring one
is a filesystem act rather than an RPC; and a deployment composing no presets
answers with an empty roster rather than an error, because sharing the host
composition is a valid deployment.

The RPC map made every registration site a type error, so the route, the
response-schema table, the service delegate, and the browser fixture are all
wired rather than only the ones I remembered.

packages/host/apiproxy/src/api/agent-presets.schema.ts

@@ -0,0 +1,25 @@
+/**
+ * agent-presets domain zod schemas (names derived from map keys:
+ * agentPresetListRequestSchema / agentPresetListValueSchema).
+ */
+
+import { z } from 'zod'
+import type { RequestPayload, ResponseValue } from './rpc-map.ts'
+import type { Wire } from './rpc.schema.ts'
+import type { AgentPresetEntry } from './agent-presets.ts'
+
+/** AgentPresetEntry row of agentPreset.list. */
+export const agentPresetEntrySchema = z.object({
+  id: z.string().min(1),
+  trust: z.union([z.literal('system'), z.literal('user')]),
+  isDefault: z.boolean(),
+}) satisfies z.ZodType<Wire<AgentPresetEntry>>
+
+/** agentPreset.list request payload. */
+export const agentPresetListRequestSchema = z.object({
+}) satisfies z.ZodType<Wire<RequestPayload<'agentPreset.list'>>>
+
+/** agentPreset.list response value. */
+export const agentPresetListValueSchema = z.object({
+  presets: z.array(agentPresetEntrySchema),
+}) satisfies z.ZodType<Wire<ResponseValue<'agentPreset.list'>>>

packages/host/apiproxy/src/api/agent-presets.ts

@@ -0,0 +1,31 @@
+/**
+ * agent-presets domain contract: the roster a browser offers when starting a
+ * session. Read-only — a preset is a composition on disk, and authoring one is
+ * a filesystem act rather than an RPC.
+ */
+
+import type { RpcRequest, RpcResponse } from './rpc.ts'
+
+/** One preset the deployment can compose a session's agent from. */
+export interface AgentPresetEntry {
+  /** Stable identifier, also the display name until presets carry metadata. */
+  readonly id: string
+  /**
+   * Whether the preset ships with the deployment or was authored locally.
+   * A `user` preset is exactly as privileged as the plugins it names, so a
+   * surface offering one should say so rather than present it as vetted.
+   */
+  readonly trust: 'system' | 'user'
+  /** Whether a session that names no preset gets this one. */
+  readonly isDefault: boolean
+}
+
+/** agent-preset-domain unary methods (the map key agentPreset.* of RpcMethodMap). */
+export interface AgentPresetsApi {
+  /**
+   * Lists every preset the deployment currently supplies, ordered by id.
+   * An empty roster means the deployment composes no presets at all, and
+   * every session shares the host composition.
+   */
+  list(request: RpcRequest<{}>): Promise<RpcResponse<{ presets: readonly AgentPresetEntry[] }>>
+}

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

@@ -8,6 +8,7 @@ import type { SessionsApi } from './sessions.ts'
 import type { HostApi } from './host.ts'
 import type { WorkspaceApi } from './workspace.ts'
 import type { CommandsApi } from './commands.ts'
+import type { AgentPresetsApi } from './agent-presets.ts'
 import type { SkillsApi } from './skills.ts'
 import type { SubagentsApi } from './subagents.ts'
 import type { EventsApi } from './events.ts'
@@ -25,6 +26,7 @@ export interface ApiProxy {
   workspace: WorkspaceApi
   commands: CommandsApi
   skills: SkillsApi
+  agentPresets: AgentPresetsApi
   events: EventsApi
   goals: GoalsApi
   settings: SettingsApi
@@ -47,6 +49,7 @@ export type {
 export type { WorkspaceApi, WorkspaceId, WorkspaceView } from './workspace.ts'
 export type { CommandsApi, CommandDescriptor } from './commands.ts'
 export type { SkillsApi, SkillEntry } from './skills.ts'
+export type { AgentPresetsApi, AgentPresetEntry } from './agent-presets.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, SettingsPathOpView, SettingsSecretView } from './settings.ts'

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

@@ -8,6 +8,7 @@ import type { SessionsApi } from './sessions.ts'
 import type { HostApi } from './host.ts'
 import type { WorkspaceApi } from './workspace.ts'
 import type { CommandsApi } from './commands.ts'
+import type { AgentPresetsApi } from './agent-presets.ts'
 import type { SkillsApi } from './skills.ts'
 import type { GoalsApi } from './goals.ts'
 import type { SettingsApi } from './settings.ts'
@@ -50,6 +51,7 @@ export interface RpcMethodMap {
   'command.list': CommandsApi['list']
   'command.execute': CommandsApi['execute']
   'skill.list': SkillsApi['list']
+  'agentPreset.list': AgentPresetsApi['list']
   'goal.create': GoalsApi['create']
   'goal.edit': GoalsApi['edit']
   'goal.pause': GoalsApi['pause']