fix(host,client): gate the picker affordance on the advertised kind; reject non-absolute browse paths

ds-review-bot round 2. The workspace UI never consulted the advertised
directoryPicker kind: under a browse (or merge-added) backend it still
rendered 'Open local folder…' and called pickDirectory(), which the host
answers with directory-picker-unavailable. The create flow now reads
directoryPickerKind() per menu open and renders the dialog affordance only
under 'dialog' — browse (until its in-app browser UI lands) and unknown
kinds hide the entry, realizing the seam's documented default; a keyless
workspace-flow snapshot pins the hidden entry over the browse fixture.

The browse backend also resolved wire paths, silently rebasing '' or
relative parents under the host process cwd; both primitives now reject
non-absolute explicit paths with their business codes, and the seam JSDoc
carries the contract.

packages/client/ui-workspace/tests/apply.spec.ts

@@ -15,16 +15,17 @@ async function bench() {
     title: 'new', sessionIds: [], createdAt: '0', updatedAt: '0',
   }))
   const pickDirectory = vi.fn(async () => '/tmp/picked')
+  const directoryPickerKind = vi.fn(async () => 'dialog' as const)
   const startSession = vi.fn()
   const rename = vi.fn(async () => ({}))
   const insertSessionBefore = vi.fn(async () => ({}))
   const open = vi.fn()
   const clear = vi.fn()
   ctx.provide('workspaces', {
-    create, pickDirectory, startSession, rename, insertSessionBefore,
+    create, pickDirectory, directoryPickerKind, startSession, rename, insertSessionBefore,
   } as never)
   ctx.provide('sessions', { open, clear } as never)
-  return { ctx, slots: ctx.get('slots') as SlotsService, create, pickDirectory, startSession, rename, insertSessionBefore, open, clear }
+  return { ctx, slots: ctx.get('slots') as SlotsService, create, pickDirectory, directoryPickerKind, startSession, rename, insertSessionBefore, open, clear }
 }
 
 type HoleName = 'sidebar.workspaces' | 'conversation.hero.workspace' | 'conversation.empty.workspace'
@@ -75,12 +76,16 @@ describe('ui-workspace apply', () => {
     expect(b.create).toHaveBeenCalledWith({ name: 'project' })
     await browser.pickDirectory()
     expect(b.pickDirectory).toHaveBeenCalledOnce()
+    await browser.directoryPickerKind()
+    expect(b.directoryPickerKind).toHaveBeenCalledOnce()
 
     const picker = (b.slots.entries('conversation.hero.workspace')[0]!.inject as () => WorkspacePickerInjected)()
     await picker.createWorkspace({ path: '/tmp/project' })
     expect(b.create).toHaveBeenCalledWith({ path: '/tmp/project' })
     await picker.pickDirectory()
     expect(b.pickDirectory).toHaveBeenCalledTimes(2)
+    await picker.directoryPickerKind()
+    expect(b.directoryPickerKind).toHaveBeenCalledTimes(2)
   })
 
   it('unregisters every entry on teardown', async () => {