fix: keep first work preview full height during teacher welcomes

tests/e2e/fixtures/teacher-preview-layout.tsx

@@ -12,7 +12,7 @@ export function Layout() {
   const [bubble, setBubble] = useState<HTMLDivElement | null>(null);
   const [introduction, setIntroduction] = useState<HTMLDivElement | null>(null);
   const [toolbarContainer, setToolbarContainer] = useState<HTMLDivElement | null>(null);
-  const [workOpen, setWorkOpen] = useState(true);
+  const [workOpen, setWorkOpen] = useState(!new URLSearchParams(location.search).has('chat'));
   const [visible, setVisible] = useState(!new URLSearchParams(location.search).has('quiet'));
   const [open, setOpen] = useState(false);
   const [width, setWidth] = useState(508);
@@ -51,7 +51,7 @@ export function Layout() {
   return <div className="classroom-workspace flex h-screen flex-col bg-white">
     <header className="relative z-50 flex h-10 shrink-0 items-center justify-end border-b px-3" data-testid="coding-conversation-header">
       <span className="mr-auto min-w-0 truncate text-xs">布局测试项目 › hello</span>
-      <TeacherCompanion companion={companion} open={open}
+      <TeacherCompanion companion={companion} open={open} showWelcomes={!workOpen}
         onOpen={(id) => { if (id) setSelected(agents.findIndex((item) => item.teacher_id === id)); setOpen(true); }}
         onToggle={(id) => { if (!id || id === agents[selected]?.teacher_id) setOpen(!open); else { setSelected(agents.findIndex((item) => item.teacher_id === id)); setOpen(true); } }}
         bubbleRef={setBubble} introductionRef={setIntroduction} />