Green the jsdom lane for the composer-seat ResizeObserver and new StatsLine format

The seat's height publisher needs a ResizeObserver stub in every spec that
renders ConversationRoot (jsdom has none), and the two branch-tail StatsLine
assertions move to the grouped detail-row output.

packages/client/ui-conversation/tests/assembly-surfaces.spec.tsx

@@ -29,9 +29,20 @@ import { apply, inject } from '@deepseek-ai/dsh-client-ui-conversation/client'
 
 const SID = 's1' as SessionId
 
-afterEach(cleanup)
+/** jsdom has no ResizeObserver; the composer seat publishes its height through one. */
+class ResizeObserverStub {
+  observe(): void {}
+  unobserve(): void {}
+  disconnect(): void {}
+}
+
+afterEach(() => {
+  cleanup()
+  vi.unstubAllGlobals()
+})
 beforeEach(() => {
   localStorage.clear()
+  vi.stubGlobal('ResizeObserver', ResizeObserverStub)
 })
 
 const TODOS: TodoItem[] = [

packages/client/ui-conversation/tests/chat-branch-tails.spec.tsx

@@ -216,6 +216,6 @@ describe('small branch tails', () => {
     const view = render(
       <StatsLine useSession={bindSnapshotSelector(source) as unknown as StatsLineProps['useSession']} />,
     )
-    expect(view.getByText('10 tokens · 1 turns · 1 steps')).toBeTruthy()
+    expect(view.container.textContent).toBe('1 turns · 1 steps|Input 0 tok · Output 10 tok')
   })
 })

packages/client/ui-conversation/tests/chat-code-subcalls.spec.tsx

@@ -23,9 +23,20 @@ import { apply, inject } from '@deepseek-ai/dsh-client-ui-conversation/client'
 
 const SID = 's1' as SessionId
 
-afterEach(cleanup)
+/** jsdom has no ResizeObserver; the composer seat publishes its height through one. */
+class ResizeObserverStub {
+  observe(): void {}
+  unobserve(): void {}
+  disconnect(): void {}
+}
+
+afterEach(() => {
+  cleanup()
+  vi.unstubAllGlobals()
+})
 beforeEach(() => {
   localStorage.clear()
+  vi.stubGlobal('ResizeObserver', ResizeObserverStub)
 })
 
 const PROGRAM = 'const listing = await tools.bash({ command: "ls notes", description: "List notes" })\nreturn listing'

packages/client/ui-conversation/tests/chat-toolview-slot.spec.tsx

@@ -21,10 +21,21 @@ import type { ToolRowProps } from '@deepseek-ai/dsh-client-ui-conversation/clien
 
 const SID = 's1' as SessionId
 
-afterEach(cleanup)
+/** jsdom has no ResizeObserver; the composer seat publishes its height through one. */
+class ResizeObserverStub {
+  observe(): void {}
+  unobserve(): void {}
+  disconnect(): void {}
+}
+
+afterEach(() => {
+  cleanup()
+  vi.unstubAllGlobals()
+})
 // The chat store persists under its declared key; clear between cases.
 beforeEach(() => {
   localStorage.clear()
+  vi.stubGlobal('ResizeObserver', ResizeObserverStub)
 })
 
 const toolResult = (seq: number, callId: string, name: string, args = '{"command":"make build","description":"Build"}'): ToolResultNode => ({

packages/client/ui-conversation/tests/gate-branch-tails.spec.tsx

@@ -49,7 +49,7 @@ describe('render branch tails', () => {
     const view = render(
       <StatsLine useSession={bindSnapshotSelector(source) as unknown as UseSession<ConversationSnapshot>} />,
     )
-    expect(view.getByText('cache hit 0% · 15 tokens · 2 turns · 3 steps')).toBeTruthy()
+    expect(view.container.textContent).toBe('2 turns · 3 steps|Cache hit 0%|Input 9 tok · Output 6 tok')
   })
 
   it('AssistantMarkdown reasoning as the streaming tail renders the running ring', () => {

packages/client/ui-conversation/tests/skeleton.spec.tsx

@@ -28,8 +28,21 @@ function fakeWiring() {
   return { wiring: shell, sink, shell }
 }
 
-afterEach(cleanup)
-beforeEach(() => { localStorage.clear() })
+/** jsdom has no ResizeObserver; the composer seat publishes its height through one. */
+class ResizeObserverStub {
+  observe(): void {}
+  unobserve(): void {}
+  disconnect(): void {}
+}
+
+afterEach(() => {
+  cleanup()
+  vi.unstubAllGlobals()
+})
+beforeEach(() => {
+  localStorage.clear()
+  vi.stubGlobal('ResizeObserver', ResizeObserverStub)
+})
 
 const sid = (id: string) => id as SessionId
 const wid = (id: string) => id as WorkspaceId