feat(host,client): compose directory picking through slots — dual-face -native, no wire advertisement

ui-workspace's two trigger surfaces each declare a single-kind directory-flow
hole (conversation.hero.workspace.directoryFlow / sidebar.workspaces.directoryFlow,
same owner contract) and keep only the trigger and the adoption: the Open-local-
folder entry renders while the surface's hole is occupied, and the occupant
reports one picked path per open through the hole's owner conversation
(open/busy/onPicked/onCancel/onError).

directory-picker-native becomes dual-face: its browser half fills both holes
with a renderless occupant driving host.pickDirectory, so the cordis.yml row
that mounts the backend also composes the client interaction — a mismatch is
impossible and a second flow package fails at client load.

With composition wiring both sides, the host.describe.directoryPicker
advertisement and the client's kind branching lose their last consumer:
the field, WorkspacesService.directoryPickerKind(), the DirectoryPickerKind
wire type, and the picker's per-open describe read are deleted. The connection
fixture now serves a deterministic pickDirectory path so the keyless snapshot
drives the full pick-then-adopt flow. ui-workspace's hand-rolled declaration
deferral is replaced by the deferRegistration helper it duplicated.

packages/client/runtime/src/client/index.ts

@@ -23,7 +23,7 @@ export type { SessionListPhase } from './sessions/manager.ts'
 export type { WorkspaceListPhase } from './workspaces/manager.ts'
 export type { WorkspaceListState } from './workspaces/service.ts'
 export type {
-  DirectoryEntry, DirectoryListing, DirectoryPickerKind, WorkspaceId, WorkspaceView,
+  DirectoryEntry, DirectoryListing, WorkspaceId, WorkspaceView,
 } from '@deepseek-ai/dsh-client-connection/client'
 // Runtime owns the snapshot store; web-react only binds it to React.
 export { createSnapshotStore, defineStore, shallowEqual } from './contract/store.ts'

packages/client/runtime/src/client/workspaces/service.ts

@@ -2,7 +2,7 @@
 
 import type { Context } from 'cordis'
 import type {
-  DirectoryListing, DirectoryPickerKind, IApiClient, RpcError,
+  DirectoryListing, IApiClient, RpcError,
   SessionId, WorkspaceId, WorkspaceView,
 } from '@deepseek-ai/dsh-client-connection/client'
 import type { SnapshotStore } from '../contract/store.ts'
@@ -191,21 +191,6 @@ export class WorkspacesService {
     return response.result.value.path
   }
 
-  /**
-   * The directory-picking interaction the Host composed — the fact the picker
-   * UI branches on (`native` opens the native chooser; `browse` opens the
-   * in-app browser). Read per flow open: one describe round trip, no cache to
-   * go stale across reconnects.
-   * @returns the Host's advertised picker kind.
-   */
-  async directoryPickerKind(): Promise<DirectoryPickerKind> {
-    const response = await this.api.host.describe({})
-    if (!response.result.ok) {
-      throw new Error(`host describe failed: ${response.result.error.message}`)
-    }
-    return response.result.value.directoryPicker
-  }
-
   /**
    * List one directory level through the Host's `browse` capability.
    * @param path - absolute directory to list; absent lists the Host home directory.