feat(cache): capacity LRU for image cache (CACHE-2)

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/server/src/modules/cache/images.ts

@@ -9,6 +9,8 @@ import { TMDB_IMAGE_SIZES } from "@umt/contracts";
 // - 读缓存只在 use_cache(GLOBAL_IMAGE_CACHE)开启时;拉到的合法图片总是写盘(与 MP 一致);
 // - 合法图片按内容识别 MIME,拒绝非图片与 SVG;ETag = md5(内容),Cache-Control: public, max-age=7 天,If-None-Match 相同回 304;
 // - 清理:删除 mtime 早于 GLOBAL_IMAGE_CACHE_DAYS 天的文件与空目录(MP clear_temp → SystemUtils.clear)。
+// - CACHE-2 容量 LRU(我们加的):读盘命中时把 atime 显式写成当前时间(不依赖挂载的 relatime),
+//   超过 storage.budgets.imagesGb 时按 atime 从旧到新删到预算的 90%;按天清理保留作兜底。
 // 我们只代理 TMDB 图片域(MP SECURITY_IMAGE_DOMAINS 的 TMDB 项),上游失败回 502。
 
 export const TMDB_IMAGE_HOST = "image.tmdb.org";
@@ -51,6 +53,13 @@ export function imageMimeType(b: Uint8Array): string | null {
   return null;
 }
 
+interface ImageFile {
+  path: string;
+  size: number;
+  mtimeMs: number;
+  atimeMs: number;
+}
+
 export interface ImageCacheOptions {
   /** DATA_DIR/cache/images */
   dir: string;
@@ -104,7 +113,10 @@ export class ImageCache {
     if (useCache) {
       const cached = await fs.readFile(path).catch(() => null);
       const mime = cached?.length ? imageMimeType(cached) : null;
-      if (cached && mime) return { content: cached, mime };
+      if (cached && mime) {
+        void this.touch(path);
+        return { content: cached, mime };
+      }
     }
     let res: Response;
     try {
@@ -130,8 +142,18 @@ export class ImageCache {
     return { content, mime };
   }
 
-  private async files(): Promise<{ path: string; size: number; mtimeMs: number }[]> {
-    const out: { path: string; size: number; mtimeMs: number }[] = [];
+  /** 记一次访问:atime = 现在,mtime 不变(按天清理仍按写入时间) */
+  private async touch(path: string): Promise<void> {
+    try {
+      const st = await fs.stat(path);
+      await fs.utimes(path, new Date(), st.mtime);
+    } catch {
+      // 文件刚被清理等:忽略
+    }
+  }
+
+  private async files(): Promise<ImageFile[]> {
+    const out: ImageFile[] = [];
     const walk = async (d: string) => {
       let names: string[];
       try {
@@ -144,7 +166,7 @@ export class ImageCache {
         const st = await fs.stat(p).catch(() => null);
         if (!st) continue;
         if (st.isDirectory()) await walk(p);
-        else out.push({ path: p, size: st.size, mtimeMs: st.mtimeMs });
+        else if (!n.endsWith(".tmp")) out.push({ path: p, size: st.size, mtimeMs: st.mtimeMs, atimeMs: st.atimeMs });
       }
     };
     await walk(this.opts.dir);
@@ -156,6 +178,31 @@ export class ImageCache {
     return { bytes: f.reduce((a, x) => a + x.size, 0), files: f.length };
   }
 
+  /**
+   * 容量 LRU:总量超过 maxBytes 时按最近访问(atime)从旧到新删除,直到不超过 maxBytes × lowWater;
+   * 没超不动。返回删除数、释放字节与清理后用量。
+   */
+  async enforceBudget(
+    maxBytes: number,
+    lowWater = 0.9,
+  ): Promise<{ deleted: number; freedBytes: number; usedBytes: number }> {
+    const files = await this.files();
+    let used = files.reduce((a, f) => a + f.size, 0);
+    if (used <= maxBytes) return { deleted: 0, freedBytes: 0, usedBytes: used };
+    const target = Math.floor(maxBytes * lowWater);
+    files.sort((a, b) => a.atimeMs - b.atimeMs || a.mtimeMs - b.mtimeMs);
+    let deleted = 0;
+    let freed = 0;
+    for (const f of files) {
+      if (used <= target) break;
+      await fs.rm(f.path, { force: true });
+      used -= f.size;
+      freed += f.size;
+      deleted++;
+    }
+    return { deleted, freedBytes: freed, usedBytes: used };
+  }
+
   /** SystemUtils.clear(images, days):删 mtime 早于 days 天的文件,再删空目录;返回删除数 */
   async clean(days: number, now = Date.now()): Promise<number> {
     let deleted = 0;