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/connection/src/client/api.ts

@@ -8,7 +8,7 @@
 export type {
   ApiProxy, SessionsApi, SessionSummary, HostApi, EventsApi, MuxFrame, HostFrame,
   ApprovalResponsePayload, QuestionResponsePayload, HistoryEntry, ToolEventView,
-  DirectoryEntry, DirectoryListing, DirectoryPickerKind,
+  DirectoryEntry, DirectoryListing,
   WorkspaceApi, WorkspaceId, WorkspaceView,
   CommandsApi, CommandDescriptor, SkillsApi, SkillEntry,
   ModelCatalogFailure, ModelCatalogModel, ModelProviderGroup, ModelReasoning,

packages/client/connection/src/client/fixture.ts

@@ -863,12 +863,11 @@ export function createFixtureApi(options: FixtureOptions = {}): ApiProxy {
       },
     },
     host: {
-      describe: request => ok(request, { version: '0.0.0-fixture', cwd: '/tmp/fixture', attachedSessions, directoryPicker: 'browse' as const }),
-      pickDirectory: request => err(request, {
-        code: 'directory-picker-unavailable',
-        message: 'the fixture host serves the browse capability',
-        details: { capability: 'browse' },
-      }),
+      describe: request => ok(request, { version: '0.0.0-fixture', cwd: '/tmp/fixture', attachedSessions }),
+      // Deterministic native pick: the keyless lanes drive the full
+      // pick-then-adopt path without an OS chooser (design-mock content,
+      // same tree the browse primitives serve).
+      pickDirectory: request => ok(request, { path: `${FIXTURE_HOME}/Documents/project` }),
       listDirectory: (request) => {
         const target = request.payload.path ?? FIXTURE_HOME
         const children = childrenOf(target)

packages/client/connection/src/client/index.ts

@@ -13,7 +13,7 @@ import { WebApiClient } from './web-api-client.ts'
 export type {
   ApiProxy, SessionsApi, SessionSummary, HostApi, EventsApi, MuxFrame, HostFrame,
   ApprovalResponsePayload, QuestionResponsePayload, HistoryEntry, ToolEventView,
-  DirectoryEntry, DirectoryListing, DirectoryPickerKind,
+  DirectoryEntry, DirectoryListing,
   ToolCallView, ToolResultView, WorkspaceApi, WorkspaceId, WorkspaceView,
   CommandsApi, CommandDescriptor, SkillsApi, SkillEntry,
   ModelCatalogFailure, ModelCatalogModel, ModelProviderGroup, ModelReasoning,