diff --git a/apps/api/src/collab/handler.ts b/apps/api/src/collab/handler.ts
index a397ee1..47d25f9 100644
--- a/apps/api/src/collab/handler.ts
+++ b/apps/api/src/collab/handler.ts
@@ -8,6 +8,7 @@ import {
   addTeacher,
   closeRoom,
   getRequest,
+  getRoom,
   hasTeacherOnline,
   listRequests,
   openRoom,
@@ -92,8 +93,13 @@ export function handleCollabClose(ws: CollabSocket) {
       removeRequest(room.studentId)
     }
   } else if (!isTeacher(ws)) {
-    // 还在排队时关掉页面，请求也该消失
-    removeRequest(ws.data.userId)
+    // 还在排队时关掉页面，请求也该消失 —— 但只能收自己这条。同一账号可能开了两个
+    // 标签页，另一个标签页可能已经把请求接成 active（甚至已经换了一拨新请求），
+    // 不加 socket 归属和状态检查，这里会把活跃房间的请求记录连根拔起
+    const request = getRequest(ws.data.userId)
+    if (request && request.socket === ws && request.status !== "active") {
+      removeRequest(ws.data.userId)
+    }
   }
 
   broadcastRequests()
@@ -131,7 +137,7 @@ export async function handleCollabMessage(ws: CollabSocket, raw: string) {
       await handleAccept(ws, message.studentId)
       return
     case "reject":
-      handleReject(ws, message.studentId)
+      await handleReject(ws, message.studentId)
       return
     case "leave":
       handleLeave(ws)
@@ -224,6 +230,11 @@ async function handleAccept(ws: CollabSocket, studentId: unknown) {
     return
   }
 
+  // 上面这次查询是个 await 点，等待期间这条连接可能已经断开——断线时
+  // handleCollabClose 已经把它从 teacherSockets 摘掉了，用它来判断这次 accept
+  // 还作不作数。continuation 里不能再对着一个死 socket 建房间
+  if (!teacherSockets().has(ws)) return
+
   // 老师同时只能在一个房间
   if (roomOf(ws)) {
     ws.send(JSON.stringify({ type: "error", message: "请先退出当前协作" }))
@@ -231,8 +242,10 @@ async function handleAccept(ws: CollabSocket, studentId: unknown) {
   }
 
   const request = getRequest(studentId)
-  if (!request || request.status === "active") {
-    // 被别人接走了或者学生已经撤销 —— 回一份最新列表让老师端自己纠正
+  if (!request || request.status === "active" || getRoom(studentId)) {
+    // 被别人接走了、学生已经撤销，或者这个学生 id 名下已经有一个房间在挂着
+    // （正常路径走不到，是两个标签页 + 断线重连缝隙的最后一道闸）——
+    // 回一份最新列表让老师端自己纠正
     ws.send(
       JSON.stringify({ type: "requests", list: listRequests().map(serializeRequest) }),
     )
@@ -265,8 +278,21 @@ async function handleAccept(ws: CollabSocket, studentId: unknown) {
   broadcastRequests()
 }
 
-function handleReject(ws: CollabSocket, studentId: unknown) {
+async function handleReject(ws: CollabSocket, studentId: unknown) {
   if (!isTeacher(ws) || typeof studentId !== "number") return
+
+  // reject 很少见，多这一次查询不心疼；不然握手快照挡不住"连接活着期间被降级
+  // 或禁用"的老师继续掐掉排队中的求助
+  const [teacher] = await db
+    .select({ adminType: schema.user.adminType })
+    .from(schema.user)
+    .where(and(eq(schema.user.id, ws.data.userId), eq(schema.user.isDisabled, false)))
+    .limit(1)
+  if (!teacher || !TEACHER_ROLES.includes(teacher.adminType)) {
+    ws.close(1008, "Permission revoked")
+    return
+  }
+
   const request = getRequest(studentId)
   // 已经在协作中的不能靠 reject 掐掉，那是 leave 的事
   if (!request || request.status === "active") return
@@ -308,5 +334,14 @@ export function handleCollabBinary(ws: CollabSocket, data: Buffer | Uint8Array)
   const room = roomOf(ws)
   if (!room) return
   const peer = ws === room.teacherSocket ? room.studentSocket : room.teacherSocket
-  peer.send(data)
+  const sent = peer.send(data)
+  if (sent <= 0) {
+    // <= 0：背压丢帧或者对端事实上已经断了。这一帧丢了，两边的 Yjs 文档从此
+    // 悄悄分叉——教学工具里"看起来在协作、其实各看各的代码"比老实断开更糟，
+    // 不做续传，直接拆房间让双方收到 room_closed、自己决定要不要重新连
+    console.error("Collab binary forward failed, tearing down room", {
+      studentId: room.studentId,
+    })
+    teardownRoom(room, "peer_offline")
+  }
 }