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/tests/connection.spec.ts

@@ -75,7 +75,7 @@ describe('connection lifecycle', () => {
     try {
       await vi.waitFor(() => { expect(describeCalls).toBe(2) }) // retried after backoff
       expect(connected).toBe(0) // never announced during the failed generation
-      gate.resolve(ok({ version: '0', cwd: '/f', attachedSessions: 0, directoryPicker: 'browse' as const }))
+      gate.resolve(ok({ version: '0', cwd: '/f', attachedSessions: 0 }))
       await vi.waitFor(() => { expect(connected).toBe(1) })
     } finally {
       controller.stop()
@@ -199,7 +199,7 @@ describe('connection lifecycle', () => {
     controller.start()
     try {
       await vi.waitFor(() => { expect(describeCalls).toBe(3) })
-      gate.resolve(ok({ version: '0', cwd: '/f', attachedSessions: 0, directoryPicker: 'browse' as const }))
+      gate.resolve(ok({ version: '0', cwd: '/f', attachedSessions: 0 }))
       await vi.waitFor(() => { expect(connected).toBe(1) })
       expect(states).toEqual(['reconnecting', 'connected']) // two failures, one reconnecting emission
     } finally {

packages/client/connection/tests/fake-api.ts

@@ -63,8 +63,8 @@ export class FakeApiClient implements IApiClient {
     payload => Promise.resolve(ok({ selected: { provider: payload.provider, model: payload.model } }))
   onPrompt: (payload: unknown) => Promise<RpcResponse<{ accepted: true }>> = () => Promise.resolve(ok({ accepted: true as const }))
   onCancel: (payload: unknown) => Promise<RpcResponse<{ accepted: true }>> = () => Promise.resolve(ok({ accepted: true as const }))
-  onDescribe: (payload: unknown) => Promise<RpcResponse<{ version: string; cwd: string; attachedSessions: number; directoryPicker: 'native' | 'browse' }>> =
-    () => Promise.resolve(ok({ version: '0-fake', cwd: '/f', attachedSessions: 0, directoryPicker: 'browse' as const }))
+  onDescribe: (payload: unknown) => Promise<RpcResponse<{ version: string; cwd: string; attachedSessions: number }>> =
+    () => Promise.resolve(ok({ version: '0-fake', cwd: '/f', attachedSessions: 0 }))
   onPickDirectory: (payload: unknown) => Promise<RpcResponse<{ path: string | null }>> =
     () => Promise.resolve(ok({ path: null }))
   onOpenPath: (payload: unknown) => Promise<RpcResponse<{ opened: true }>> =