feat(coding): keep one ongoing conversation per delivered agent

src/pages/Chat/TeacherCompanion.tsx

@@ -28,7 +28,7 @@ export function TeacherCompanion({ companion, open, onOpen, bubbleRef }: {
         aria-controls="coding-consultation-dock" data-agent-id={agent.teacher_id}
         onMouseDown={(event) => event.preventDefault()} onClick={() => onOpen(agent.teacher_id)}>
         <span className="teacher-companion-avatar"><TeacherAvatar definition={agent.definition} />
-          {activeId === agent.teacher_id && invitation && <span className="teacher-companion-unread" aria-hidden="true" />}</span>
+          {(companion.unreadAgentIds.includes(agent.teacher_id) || (activeId === agent.teacher_id && invitation)) && <span className="teacher-companion-unread" aria-hidden="true" />}</span>
         <span className="teacher-companion-name">{agent.definition.name}</span>
         {activeId === agent.teacher_id && checking && <Loader2 className="h-3 w-3 shrink-0 animate-spin text-muted-foreground motion-reduce:animate-none" aria-label="智能体正在思考" />}
       </button>)}