fix: 应用截图按实际存在数量预览，不再固定 5 张

- useAppDetail.loadScreenshots 改为异步探测：并发 HEAD 请求 screen_1~5.png，
  仅把返回 2xx 的真实截图加入 screenshots，不足 5 张时预览计数与按钮边界自动跟随
- ScreenPreview 已有的 disabled 边界 (currentScreenIndex === screenshots.length-1)
  因此生效，切换到最后一张后禁止继续向后，消除空白页
- 新增 screenshotAbortController：打开新详情/关闭详情时取消旧探测，避免结果覆盖
- 探测异常不影响详情页弹窗，截图区域在探测完成后自动刷新/显示暂无应用截图
- debian/changelog 测试版本号 5.2.1.3-test
- 验证：vue-tsc 0 / eslint 0 / dpkg-buildpackage 打包成功

debian/changelog

@@ -1,4 +1,4 @@
-spark-store (5.2.1.2-test) UNRELEASED; urgency=medium
+spark-store (5.2.1.3-test) UNRELEASED; urgency=medium
 
   * Initial release. (Closes: #nnnn)  <nnnn is the bug number of your ITP>
 

src/composables/useAppDetail.ts

@@ -34,6 +34,7 @@ import {
   buildReviewTags,
 } from "../modules/appIdentity";
 import { loadFavoriteMetadataForDetail } from "./useFavorites";
+import { axiosInstance } from "./useHttp";
 import type { ReviewTags } from "../global/typedefinition";
 import type { Ref } from "vue";
 
@@ -54,6 +55,9 @@ const currentReviewTags = computed<ReviewTags | null>(() => {
   });
 });
 
+// 截图探测请求的中断控制器：每次打开新详情前取消旧探测，避免结果覆盖当前应用。
+let screenshotAbortController: AbortController | null = null;
+
 // 从仓库获取应用详细信息的辅助函数
 const fetchAppFromStore = async (
   pkgname: string,
@@ -329,7 +333,10 @@ const openDetail = async (app: App | OpenDetailInput) => {
 
   currentApp.value = finalApp;
   currentScreenIndex.value = 0;
-  loadScreenshots(displayAppForScreenshots);
+  // 截图异步探测，详情页先弹出不阻塞；探测完成后截图区域自动刷新
+  loadScreenshots(displayAppForScreenshots).catch(() => {
+    // 异常（含取消）已在 loadScreenshots 内处理，此处仅避免未捕获 promise
+  });
   showModal.value = true;
 
   currentAppSparkInstalled.value = false;
@@ -386,19 +393,60 @@ const checkAppInstalled = (app: App) => {
   }
 };
 
-const loadScreenshots = (app: App) => {
+// 探测单张截图是否真实存在：用 HEAD 请求，超时 3s，仅当返回 2xx 时视为有效。
+// 使用 axiosInstance 以便复用同源配置，但 HEAD PNG 不会触发 .json 缓存穿透拦截器。
+const checkScreenshotExists = async (
+  url: string,
+  signal?: AbortSignal,
+): Promise<boolean> => {
+  try {
+    await axiosInstance.head(url, { timeout: 3000, signal });
+    return true;
+  } catch {
+    return false;
+  }
+};
+
+const loadScreenshots = async (app: App) => {
+  // 取消上一应用的截图探测，避免结果覆盖到当前应用
+  if (screenshotAbortController) {
+    screenshotAbortController.abort();
+  }
+  const controller = new AbortController();
+  screenshotAbortController = controller;
+
   screenshots.value = [];
+  if (!app.category || app.category === "unknown") return;
   const arch = window.apm_store.arch || "amd64";
   const finalArch = app.origin === "spark" ? `${arch}-store` : `${arch}-apm`;
+
+  const candidates: string[] = [];
   for (let i = 1; i <= 5; i++) {
-    const screenshotUrl = `${APM_STORE_BASE_URL}/${finalArch}/${app.category}/${app.pkgname}/screen_${i}.png`;
-    screenshots.value.push(screenshotUrl);
+    candidates.push(
+      `${APM_STORE_BASE_URL}/${finalArch}/${app.category}/${app.pkgname}/screen_${i}.png`,
+    );
+  }
+
+  try {
+    // 并发探测 5 张候选截图，只保留真实存在的；失败视为无该图，不阻塞详情页打开。
+    const results = await Promise.all(
+      candidates.map((url) => checkScreenshotExists(url, controller.signal)),
+    );
+    const valid = candidates.filter((_, index) => results[index]);
+    screenshots.value = valid;
+  } catch {
+    // 当前轮次被新详情页取消或异常：不写入旧结果
   }
 };
 
 const closeDetail = () => {
   showModal.value = false;
   currentApp.value = null;
+  // 关闭详情时取消正在进行的截图探测，避免结果写入已关闭的旧应用
+  if (screenshotAbortController) {
+    screenshotAbortController.abort();
+    screenshotAbortController = null;
+  }
 };
 
 const openScreenPreview = (index: number) => {