feat(host): directory-picker capability seam with dialog and browse backends

The web GUI's folder picking was hardwired to one interaction: a native
OS chooser compiled into the gateway, unusable for remote deployments
and swappable only by editing apiproxy source.

Directory picking becomes a three-package capability seam in
packages/host: ctx.directoryPicker returns a discriminated capability —
dialog (the extracted native chooser; host-display only) or browse
(new: one-level listing + child creation over Node stdlib, hidden flags
host-stamped, symlinks followed, ancestry crumbs; remote-capable). The
gateway injects the seam, advertises the kind via
host.describe.directoryPicker, serves host.listDirectory /
host.createDirectory under browse, and answers
directory-picker-unavailable across kinds. cordis.yml is the swap
point; apps/cli keeps dialog mounted, so behavior is unchanged until
the in-app browser PR flips the default. The connection fixture serves
a deterministic browse tree; WorkspacesService gains the browse calls
the browser UI will drive. Decision record:
.agents/notes/implemented/architecture/2026-07-28-directory-picker-capability-seam.md

packages/host/apiproxy/src/fetch/client.ts

@@ -13,7 +13,10 @@ import { RpcId } from '../api/rpc.ts'
 import type { Wire } from '../api/rpc.schema.ts'
 import { rpcReceiptSchema, serverRequestSchema, serverResponseSchema } from '../api/rpc.schema.ts'
 import { hostFrameSchema, muxFrameSchema } from '../api/events.schema.ts'
-import { hostDescribeValueSchema, hostPickDirectoryValueSchema } from '../api/host.schema.ts'
+import {
+  hostCreateDirectoryValueSchema, hostDescribeValueSchema,
+  hostListDirectoryValueSchema, hostPickDirectoryValueSchema,
+} from '../api/host.schema.ts'
 import {
   sessionCancelValueSchema,
   sessionCreateValueSchema,
@@ -61,6 +64,8 @@ export interface IApiClient {
   host: {
     describe(payload: RequestPayload<'host.describe'>, signal?: AbortSignal): Promise<RpcResponse<ResponseValue<'host.describe'>>>
     pickDirectory(payload: RequestPayload<'host.pickDirectory'>, signal?: AbortSignal): Promise<RpcResponse<ResponseValue<'host.pickDirectory'>>>
+    listDirectory(payload: RequestPayload<'host.listDirectory'>, signal?: AbortSignal): Promise<RpcResponse<ResponseValue<'host.listDirectory'>>>
+    createDirectory(payload: RequestPayload<'host.createDirectory'>, signal?: AbortSignal): Promise<RpcResponse<ResponseValue<'host.createDirectory'>>>
   }
   workspace: {
     list(payload: RequestPayload<'workspace.list'>, signal?: AbortSignal): Promise<RpcResponse<ResponseValue<'workspace.list'>>>
@@ -98,6 +103,8 @@ const UNARY_VALUE_SCHEMAS: { [K in keyof RpcMethodMap]: z.ZodType<Wire<ResponseV
   'session.cancel': sessionCancelValueSchema,
   'host.describe': hostDescribeValueSchema,
   'host.pickDirectory': hostPickDirectoryValueSchema,
+  'host.listDirectory': hostListDirectoryValueSchema,
+  'host.createDirectory': hostCreateDirectoryValueSchema,
   'workspace.list': workspaceListValueSchema,
   'workspace.create': workspaceCreateValueSchema,
   'workspace.rename': workspaceRenameValueSchema,
@@ -305,6 +312,8 @@ export abstract class AbstractApiClient implements IApiClient {
     // A native system dialog is user-paced and may legitimately stay open
     // longer than the normal unary deadline. Caller/connection aborts remain.
     pickDirectory: (payload, signal) => this.callUnary('host.pickDirectory', payload, signal, false),
+    listDirectory: (payload, signal) => this.callUnary('host.listDirectory', payload, signal),
+    createDirectory: (payload, signal) => this.callUnary('host.createDirectory', payload, signal),
   }
 
   readonly workspace: IApiClient['workspace'] = {

packages/host/apiproxy/src/fetch/handler.ts

@@ -23,7 +23,10 @@ import {
   sessionPromptRequestSchema,
   sessionSelectModelRequestSchema,
 } from '../api/sessions.schema.ts'
-import { hostDescribeRequestSchema, hostPickDirectoryRequestSchema } from '../api/host.schema.ts'
+import {
+  hostCreateDirectoryRequestSchema, hostDescribeRequestSchema,
+  hostListDirectoryRequestSchema, hostPickDirectoryRequestSchema,
+} from '../api/host.schema.ts'
 import {
   workspaceCreateRequestSchema,
   workspaceDeleteRequestSchema,
@@ -60,6 +63,8 @@ const UNARY_ROUTES: UnaryRoutes = {
   'session.cancel': { schema: sessionCancelRequestSchema, invoke: (api, r) => api.sessions.cancel(r) },
   'host.describe': { schema: hostDescribeRequestSchema, invoke: (api, r) => api.host.describe(r) },
   'host.pickDirectory': { schema: hostPickDirectoryRequestSchema, invoke: (api, r, signal) => api.host.pickDirectory(r, signal) },
+  'host.listDirectory': { schema: hostListDirectoryRequestSchema, invoke: (api, r) => api.host.listDirectory(r) },
+  'host.createDirectory': { schema: hostCreateDirectoryRequestSchema, invoke: (api, r) => api.host.createDirectory(r) },
   'workspace.list': { schema: workspaceListRequestSchema, invoke: (api, r) => api.workspace.list(r) },
   'workspace.create': { schema: workspaceCreateRequestSchema, invoke: (api, r) => api.workspace.create(r) },
   'workspace.rename': { schema: workspaceRenameRequestSchema, invoke: (api, r) => api.workspace.rename(r) },