fix: 批改页 J/K 按键位对调；预览换内容不再进浏览器历史，“后退”能回到作品墙

- J 上一个、K 下一个，和面板上的左右箭头一致
- 打开的作品放进地址栏（?sub=）：点开记一步历史，J/K 切换只替换，关闭 / Esc 退回那一步
- 所有会换内容的预览 iframe 加 key，换内容时换新的 iframe：在原 iframe 里改 srcdoc 是一次导航，
  会进浏览器历史，“后退”就成了在预览里倒退（批改页切换学生、挑战页改代码都会这样）

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -32,7 +32,7 @@ The backend was rewritten from Django in 2026-10 to cut memory use (~25 MB vs. 1
   - `src/icons.ts` — `<Icon icon="lucide:name" />` renders bundled `lucide-vue-next` icons (works offline); register new names in its map. Fonts are bundled too (`@fontsource/jetbrains-mono`)
   - `components/workbench/Workbench.vue` — shared challenge / creation page: left = brief + AI chat (`PromptPanel`), right = preview / code (`CodeTabs`) + `VersionBar`. Every assistant message with code is a version; hand edits and pasted external-AI code are saved as versions via `POST /prompt/versions` (`source` `edit` / `manual`, stored as a user+assistant pair). Challenges are submitted only when the student clicks “交这一版” (`POST /submission/` with `message_id`), never automatically. Editor code is per task (`composables/useTaskCode.ts`, localStorage `web-code:<user>:<task>`); the tutorial page edits the shared `store/editors.ts` refs but `Workspace.vue` saves them under the same per-task key and `TutorialContent` restores them (example code only the first time)
   - `pages/ChallengeHome.vue` — challenge list page; `pages/TaskEditor.vue` (prop `kind`) is the single tutorial / challenge authoring page
-  - `pages/Review.vue` (“批改”, default teaching page) + `components/review/ReviewPanel.vue` (also opened from the gradebook) — opens as a large preview (wall hidden, Esc returns; “小面板” switches to a side panel, remembered); keys: J/K next/prev student, 1–5 rate, P present; “全部班级” groups the wall by class; `components/review/PeersDrawer.vue` is the students' “同学作品” (本班 / 全部班级)
+  - `pages/Review.vue` (“批改”, default teaching page) + `components/review/ReviewPanel.vue` (also opened from the gradebook) — opens as a large preview (wall hidden, Esc returns; “小面板” switches to a side panel, remembered); keys: J/K previous/next student (by key position), 1–5 rate, P present; “全部班级” groups the wall by class; `components/review/PeersDrawer.vue` is the students' “同学作品” (本班 / 全部班级)
   - `components/layout/AppShell.vue` — top bar for every page; `pages/Dashboard.vue` is the teaching sidebar (“教学”) under `/dashboard`
   - `src/store/` — Reactive state (plain Vue refs, not Vuex/Pinia); `prompt.ts` / `guidance.ts` own the WebSockets
   - `src/pages/`, `src/components/` — user management uses `components/dashboard/UserFormModal.vue` (there is no Django Admin anymore)

client/src/components/editor/Preview.vue

@@ -46,6 +46,7 @@
       ref="frame"
       class="iframe"
       :sandbox="PREVIEW_SANDBOX"
+      :key="frameKey"
       :srcdoc="previewContent"
     ></iframe>
   </div>
@@ -141,8 +142,12 @@ function getContent(forDownload = false) {
   })
 }
 
+// 每次内容变了换一个新的 iframe：在同一个 iframe 里改 srcdoc 会进浏览器历史，
+// 按“后退”就成了在预览里倒退，而不是离开页面
+const frameKey = ref(0)
 function preview() {
   previewContent.value = getContent()
+  frameKey.value++
 }
 
 function download() {

client/src/components/review/PeersDrawer.vue

@@ -61,7 +61,7 @@
     @update:show="(v: boolean) => !v && (large = null)"
   >
     <div v-if="large" class="large">
-      <iframe :sandbox="PREVIEW_SANDBOX" :srcdoc="docOf(large)"></iframe>
+      <iframe :key="large.id" :sandbox="PREVIEW_SANDBOX" :srcdoc="docOf(large)"></iframe>
     </div>
   </n-modal>
 </template>

client/src/components/review/ReviewPanel.vue

@@ -13,7 +13,7 @@
                 <Icon icon="lucide:arrow-left" />
               </n-button>
             </template>
-            上一个学生（K）
+            上一个学生（J）
           </n-tooltip>
           <n-tooltip>
             <template #trigger>
@@ -21,7 +21,7 @@
                 <Icon icon="lucide:arrow-right" />
               </n-button>
             </template>
-            下一个学生（J）
+            下一个学生（K）
           </n-tooltip>
         </template>
         <n-button
@@ -61,7 +61,8 @@
           </button>
         </div>
         <div class="frame">
-          <iframe :sandbox="PREVIEW_SANDBOX" :srcdoc="doc"></iframe>
+          <!-- key：换作品时换新的 iframe，不进浏览器历史 -->
+          <iframe :key="currentId" :sandbox="PREVIEW_SANDBOX" :srcdoc="doc"></iframe>
         </div>
         <n-flex justify="space-between" align="center" class="meta">
           <span class="muted">

client/src/components/workbench/RatingCard.vue

@@ -10,6 +10,7 @@
     <div v-else-if="current" class="body">
       <button class="thumb" title="点击放大看" @click="showLarge = true">
         <iframe
+          :key="current.submission_id"
           :sandbox="PREVIEW_SANDBOX"
           :srcdoc="doc"
           tabindex="-1"
@@ -39,7 +40,7 @@
     style="width: 90vw; max-width: 1000px"
   >
     <div class="large">
-      <iframe :sandbox="PREVIEW_SANDBOX" :srcdoc="doc"></iframe>
+      <iframe :key="current?.submission_id" :sandbox="PREVIEW_SANDBOX" :srcdoc="doc"></iframe>
     </div>
     <div class="large-rates">
       <button

client/src/pages/Review.vue

@@ -71,11 +71,12 @@
               :key="s.user_id"
               :class="['card', { sel: s.submission?.id === selectedId, missing: !s.submission }]"
               :disabled="!s.submission"
-              @click="s.submission && (selectedId = s.submission.id)"
+              @click="s.submission && openDetail(s.submission.id)"
             >
               <div class="thumb">
                 <iframe
                   v-if="s.submission"
+                  :key="s.submission.id"
                   :sandbox="PREVIEW_SANDBOX"
                   :srcdoc="docOf(s)"
                   loading="lazy"
@@ -112,7 +113,7 @@
         :nav="{ prev: neighbor(-1) !== null, next: neighbor(1) !== null }"
         @prev="move(-1)"
         @next="move(1)"
-        @close="selectedId = null"
+        @close="closeDetail"
         @changed="applyPatch"
       />
     </aside>
@@ -127,6 +128,7 @@
     <iframe
       v-if="presentList[presentIndex]"
       :sandbox="PREVIEW_SANDBOX"
+      :key="presentIndex"
       :srcdoc="docOf(presentList[presentIndex]!)"
     ></iframe>
   </div>
@@ -152,7 +154,31 @@ const loadingWall = ref(false)
 const classname = ref<string | null>((route.query.class as string) || null)
 const taskId = ref<number | null>(route.query.task ? Number(route.query.task) : null)
 const filter = ref<"all" | "unrated" | "missing" | "present">("all")
-const selectedId = ref<string | null>(null)
+// 打开的作品放在地址栏（?sub=），浏览器“后退”就能回到作品墙
+const selectedId = ref<string | null>((route.query.sub as string) || null)
+watch(
+  () => route.query.sub,
+  (v) => {
+    selectedId.value = (v as string) || null
+  },
+)
+// 是不是从作品墙点开的（点开时记了一步历史，关闭时退回那一步）
+let pushedDetail = false
+
+function openDetail(id: string) {
+  pushedDetail = true
+  router.push({ query: { ...route.query, sub: id } })
+}
+
+function closeDetail() {
+  if (pushedDetail) {
+    pushedDetail = false
+    router.back()
+  } else {
+    const { sub: _, ...rest } = route.query
+    router.replace({ query: rest })
+  }
+}
 const presenting = ref(false)
 // 点开作品默认用大图（预览占满中间），老师也可以切回旁边的小面板；记住选择
 const bigPreview = useStorage("review-big-preview", true)
@@ -251,7 +277,7 @@ watch(classname, (c) => {
 })
 watch([classname, taskId], () => {
   router.replace({ query: { class: classname.value ?? undefined, task: taskId.value ?? undefined } })
-  selectedId.value = null
+  pushedDetail = false
   filter.value = "all"
   students.value = []
   loadWall()
@@ -263,9 +289,10 @@ function neighbor(step: number): string | null {
   const i = list.findIndex((s) => s.submission!.id === selectedId.value)
   return list[i + step]?.submission?.id ?? null
 }
+// 切换学生不新增历史，免得要连按很多次后退
 function move(step: number) {
   const id = neighbor(step)
-  if (id) selectedId.value = id
+  if (id) router.replace({ query: { ...route.query, sub: id } })
 }
 
 function applyPatch(p: { id: string; my_score?: number; score?: number; flag?: FlagType }) {
@@ -290,9 +317,10 @@ function onKey(e: KeyboardEvent) {
   }
   const t = e.target as HTMLElement
   if (t.closest("input, textarea, [contenteditable]") || e.ctrlKey || e.metaKey || e.altKey) return
-  if (e.key === "Escape" && selectedId.value) selectedId.value = null
-  else if (e.key === "j" || e.key === "J") move(1)
-  else if (e.key === "k" || e.key === "K") move(-1)
+  if (e.key === "Escape" && selectedId.value) closeDetail()
+  // 按键盘上的位置：J 在左边是上一个，K 在右边是下一个（和面板上的左右箭头一致）
+  else if (e.key === "j" || e.key === "J") move(-1)
+  else if (e.key === "k" || e.key === "K") move(1)
 }
 
 onMounted(async () => {

client/src/pages/Submission.vue

@@ -24,7 +24,7 @@ async function init() {
 onMounted(init)
 </script>
 <template>
-  <iframe class="iframe" :sandbox="PREVIEW_SANDBOX" :srcdoc="content"></iframe>
+  <iframe v-if="content" class="iframe" :sandbox="PREVIEW_SANDBOX" :srcdoc="content"></iframe>
 </template>
 <style scoped>
 .iframe {