diff --git a/.changeset/url-load-proxy-revalidate.md b/.changeset/url-load-proxy-revalidate.md
new file mode 100644
index 000000000..6fd373c09
--- /dev/null
+++ b/.changeset/url-load-proxy-revalidate.md
@@ -0,0 +1,5 @@
+---
+'@be-music/worker-play': patch
+---
+
+An embed `?track=` or player `?music=` archive from another origin was downloaded in full on every load, because `/__url-load-proxy` answered `no-store` and dropped the host's validators. The proxy now answers `no-cache` and passes `ETag` / `Last-Modified` and the browser's `If-None-Match` / `If-Modified-Since` through, so an unchanged archive comes back as a 304 from the browser's cache.
diff --git a/docs/player-web.ja.md b/docs/player-web.ja.md
index 8c6d471a2..042cc97bb 100644
--- a/docs/player-web.ja.md
+++ b/docs/player-web.ja.md
@@ -875,7 +875,7 @@ PixiJS scene wiring は browser rendering や WebAudio resource に依存する
 
 ## 埋め込みプレビュー
 
-`/embed/?track=<URL>`（`play.be-music.app`、プレビュー環境は `play.preview.be-music.app`）は、譜面のアーカイブを iframe の中でプレビューする。`@be-music/app-play` の 2 つ目のエントリ（`embed/index.html`、`src/embed/`）で、同じ Worker が配信する。Worker は iframe では自動サインインを始めない。アーカイブは `?music=` と同じく、同じオリジンからは直接、別の https オリジンからは `/__url-load-proxy` を経由して取得する。
+`/embed/?track=<URL>`（`play.be-music.app`、プレビュー環境は `play.preview.be-music.app`）は、譜面のアーカイブを iframe の中でプレビューする。`@be-music/app-play` の 2 つ目のエントリ（`embed/index.html`、`src/embed/`）で、同じ Worker が配信する。Worker は iframe では自動サインインを始めない。アーカイブは `?music=` と同じく、同じオリジンからは直接、別の https オリジンからは `/__url-load-proxy` を経由して取得する。ブラウザはアーカイブを保存し、読み込むたびに再検証する。プロキシは `no-cache` を付け、配信元の `ETag` / `Last-Modified` とブラウザの条件付きリクエストを中継するので、変わっていないアーカイブはダウンロードし直さない。どちらの検証子も送らない配信元からは毎回ダウンロードする。
 
 ```html
 <iframe
diff --git a/docs/player-web.md b/docs/player-web.md
index c2317a719..b24846ac6 100644
--- a/docs/player-web.md
+++ b/docs/player-web.md
@@ -878,7 +878,7 @@ PixiJS scene wiring can remain in `player-browser` when the behavior depends on
 
 ## Embedded preview
 
-`/embed/?track=<URL>` (`play.be-music.app`, and `play.preview.be-music.app` for the preview environment) previews a chart archive inside an iframe. It is a second entry of `@be-music/app-play` (`embed/index.html`, `src/embed/`), served by the same Worker; the Worker starts no automatic sign-in for an iframe. The archive is fetched like `?music=`: directly from this origin, through `/__url-load-proxy` from another https origin.
+`/embed/?track=<URL>` (`play.be-music.app`, and `play.preview.be-music.app` for the preview environment) previews a chart archive inside an iframe. It is a second entry of `@be-music/app-play` (`embed/index.html`, `src/embed/`), served by the same Worker; the Worker starts no automatic sign-in for an iframe. The archive is fetched like `?music=`: directly from this origin, through `/__url-load-proxy` from another https origin. The browser keeps the archive and revalidates it on each load: the proxy marks it `no-cache` and passes the host's `ETag` / `Last-Modified` and the browser's conditional request through, so an unchanged archive is not downloaded again. A host that sends neither validator is downloaded every time.
 
 ```html
 <iframe
diff --git a/packages/worker-play/src/index.ts b/packages/worker-play/src/index.ts
index e8601af8e..c069f2581 100644
--- a/packages/worker-play/src/index.ts
+++ b/packages/worker-play/src/index.ts
@@ -18,6 +18,7 @@
 import { handleAuth, readSession, type OIDCEnv } from '@be-music/service-auth-client';
 import { isLeaderboardPath } from './leaderboard-paths.ts';
 import { handlePlayerSettings, PLAYER_SETTINGS_PATH } from './player-settings.ts';
+import { serveURLLoadProxy } from './url-load-proxy.ts';
 
 interface Env extends OIDCEnv {
   ASSETS: Fetcher;
@@ -69,56 +70,6 @@ async function serveFFmpegCore(request: Request, env: Env, pathname: string): Pr
   return new Response(request.method === 'HEAD' ? null : object.body, { headers });
 }
 
-function resolveURLLoadProxyTarget(rawURL: string | null): URL {
-  if (!rawURL) {
-    throw new Error('missing url query parameter');
-  }
-  const target = new URL(rawURL);
-  if (target.protocol !== 'https:') {
-    throw new Error('only https proxy targets are allowed');
-  }
-  if (target.username || target.password) {
-    throw new Error('proxy target credentials are not allowed');
-  }
-  return target;
-}
-
-async function serveURLLoadProxy(request: Request): Promise<Response> {
-  if (request.method !== 'GET' && request.method !== 'HEAD') {
-    return new Response('Method Not Allowed', { status: 405, headers: { Allow: 'GET, HEAD' } });
-  }
-
-  let target: URL;
-  try {
-    target = resolveURLLoadProxyTarget(new URL(request.url).searchParams.get('url'));
-  } catch (error) {
-    return new Response(error instanceof Error ? error.message : 'invalid proxy target', { status: 400 });
-  }
-
-  let upstream: Response;
-  try {
-    upstream = await fetch(target, {
-      method: request.method === 'HEAD' ? 'HEAD' : 'GET',
-      redirect: 'follow',
-    });
-  } catch (error) {
-    return new Response(`failed to fetch ${target.href}: ${error instanceof Error ? error.message : String(error)}`, {
-      status: 502,
-    });
-  }
-
-  const headers = new Headers();
-  headers.set('content-type', upstream.headers.get('content-type') ?? 'application/octet-stream');
-  headers.set('cache-control', 'no-store');
-  headers.set('cross-origin-resource-policy', 'same-origin');
-
-  return new Response(request.method === 'HEAD' ? null : upstream.body, {
-    status: upstream.status,
-    statusText: upstream.statusText,
-    headers,
-  });
-}
-
 export default {
   async fetch(request: Request, env: Env): Promise<Response> {
     const auth = await handleAuth(request, env);
diff --git a/packages/worker-play/src/url-load-proxy.test.ts b/packages/worker-play/src/url-load-proxy.test.ts
new file mode 100644
index 000000000..67623537e
--- /dev/null
+++ b/packages/worker-play/src/url-load-proxy.test.ts
@@ -0,0 +1,74 @@
+import { describe, expect, test } from 'vite-plus/test';
+import { resolveURLLoadProxyTarget, serveURLLoadProxy } from './url-load-proxy.ts';
+
+const ARCHIVE = 'https://example.com/song.zip';
+const proxyURL = (url: string) => `https://play.be-music.app/__url-load-proxy?url=${encodeURIComponent(url)}`;
+
+/** A fake upstream recording what it was asked: 304 when the request's If-None-Match is its ETag. */
+function upstream(etag: string) {
+  const requests: { url: string; headers: Headers }[] = [];
+  const fetcher = async (input: URL, init: RequestInit): Promise<Response> => {
+    const headers = new Headers(init.headers);
+    requests.push({ url: input.href, headers });
+    const validators = { etag, 'last-modified': 'Sat, 31 Oct 2026 00:00:00 GMT' };
+    if (headers.get('if-none-match') === etag) return new Response(null, { status: 304, headers: validators });
+    return new Response('zip', { headers: { ...validators, 'content-type': 'application/zip' } });
+  };
+  return { requests, fetcher };
+}
+
+describe('serveURLLoadProxy', () => {
+  test('passes the archive through with its validators, cached but revalidated each time', async () => {
+    const { requests, fetcher } = upstream('"v1"');
+    const response = await serveURLLoadProxy(new Request(proxyURL(ARCHIVE)), fetcher);
+    expect(response.status).toBe(200);
+    expect(await response.text()).toBe('zip');
+    expect(response.headers.get('cache-control')).toBe('no-cache');
+    expect(response.headers.get('etag')).toBe('"v1"');
+    expect(response.headers.get('last-modified')).toBe('Sat, 31 Oct 2026 00:00:00 GMT');
+    expect(response.headers.get('content-type')).toBe('application/zip');
+    expect(requests[0]!.url).toBe(ARCHIVE);
+  });
+
+  test("answers an unchanged archive's revalidation with a bodiless 304", async () => {
+    const { requests, fetcher } = upstream('"v1"');
+    const request = new Request(proxyURL(ARCHIVE), {
+      headers: { 'if-none-match': '"v1"', 'if-modified-since': 'Sat, 31 Oct 2026 00:00:00 GMT' },
+    });
+    const response = await serveURLLoadProxy(request, fetcher);
+    expect(response.status).toBe(304);
+    expect(response.body).toBeNull();
+    expect(response.headers.get('etag')).toBe('"v1"');
+    expect(requests[0]!.headers.get('if-none-match')).toBe('"v1"');
+    expect(requests[0]!.headers.get('if-modified-since')).toBe('Sat, 31 Oct 2026 00:00:00 GMT');
+  });
+
+  test('downloads a changed archive again', async () => {
+    const { fetcher } = upstream('"v2"');
+    const request = new Request(proxyURL(ARCHIVE), { headers: { 'if-none-match': '"v1"' } });
+    const response = await serveURLLoadProxy(request, fetcher);
+    expect(response.status).toBe(200);
+    expect(response.headers.get('etag')).toBe('"v2"');
+  });
+
+  test('forwards no other browser header, such as cookies', async () => {
+    const { requests, fetcher } = upstream('"v1"');
+    await serveURLLoadProxy(new Request(proxyURL(ARCHIVE), { headers: { cookie: 'session=1' } }), fetcher);
+    expect([...requests[0]!.headers.keys()]).toEqual([]);
+  });
+
+  test('refuses other methods and targets it must not fetch', async () => {
+    const { fetcher } = upstream('"v1"');
+    expect((await serveURLLoadProxy(new Request(proxyURL(ARCHIVE), { method: 'POST' }), fetcher)).status).toBe(405);
+    expect((await serveURLLoadProxy(new Request(proxyURL('http://example.com/a.zip')), fetcher)).status).toBe(400);
+  });
+});
+
+describe('resolveURLLoadProxyTarget', () => {
+  test('accepts https URLs only, without credentials', () => {
+    expect(resolveURLLoadProxyTarget(ARCHIVE).href).toBe(ARCHIVE);
+    expect(() => resolveURLLoadProxyTarget(null)).toThrow('missing url');
+    expect(() => resolveURLLoadProxyTarget('http://example.com/a.zip')).toThrow('only https');
+    expect(() => resolveURLLoadProxyTarget('https://user:pass@example.com/a.zip')).toThrow('credentials');
+  });
+});
diff --git a/packages/worker-play/src/url-load-proxy.ts b/packages/worker-play/src/url-load-proxy.ts
new file mode 100644
index 000000000..d5416f07b
--- /dev/null
+++ b/packages/worker-play/src/url-load-proxy.ts
@@ -0,0 +1,75 @@
+// `/__url-load-proxy?url=<https URL>`: fetches an archive from another origin for the player's `?music=` and the embed's
+// `?track=`, whose hosts often send no CORS headers. The browser may keep the response but revalidates it on every use
+// (`no-cache`): the upstream's ETag / Last-Modified pass through, and so do the browser's If-None-Match /
+// If-Modified-Since, so an unchanged archive comes back as a 304 instead of downloading again.
+
+/** The validators the proxy carries from the browser to the upstream. */
+const CONDITIONAL_REQUEST_HEADERS = ['if-none-match', 'if-modified-since'] as const;
+/** The validators the proxy carries from the upstream back to the browser. */
+const VALIDATOR_RESPONSE_HEADERS = ['etag', 'last-modified'] as const;
+
+export function resolveURLLoadProxyTarget(rawURL: string | null): URL {
+  if (!rawURL) {
+    throw new Error('missing url query parameter');
+  }
+  const target = new URL(rawURL);
+  if (target.protocol !== 'https:') {
+    throw new Error('only https proxy targets are allowed');
+  }
+  if (target.username || target.password) {
+    throw new Error('proxy target credentials are not allowed');
+  }
+  return target;
+}
+
+export async function serveURLLoadProxy(
+  request: Request,
+  fetcher: (input: URL, init: RequestInit) => Promise<Response> = fetch,
+): Promise<Response> {
+  if (request.method !== 'GET' && request.method !== 'HEAD') {
+    return new Response('Method Not Allowed', { status: 405, headers: { Allow: 'GET, HEAD' } });
+  }
+
+  let target: URL;
+  try {
+    target = resolveURLLoadProxyTarget(new URL(request.url).searchParams.get('url'));
+  } catch (error) {
+    return new Response(error instanceof Error ? error.message : 'invalid proxy target', { status: 400 });
+  }
+
+  const conditional = new Headers();
+  for (const name of CONDITIONAL_REQUEST_HEADERS) {
+    const value = request.headers.get(name);
+    if (value !== null) conditional.set(name, value);
+  }
+
+  let upstream: Response;
+  try {
+    upstream = await fetcher(target, {
+      method: request.method === 'HEAD' ? 'HEAD' : 'GET',
+      headers: conditional,
+      redirect: 'follow',
+    });
+  } catch (error) {
+    return new Response(`failed to fetch ${target.href}: ${error instanceof Error ? error.message : String(error)}`, {
+      status: 502,
+    });
+  }
+
+  const headers = new Headers();
+  headers.set('content-type', upstream.headers.get('content-type') ?? 'application/octet-stream');
+  // Keep it, but ask again each time: the same URL may serve a new archive.
+  headers.set('cache-control', 'no-cache');
+  headers.set('cross-origin-resource-policy', 'same-origin');
+  for (const name of VALIDATOR_RESPONSE_HEADERS) {
+    const value = upstream.headers.get(name);
+    if (value !== null) headers.set(name, value);
+  }
+
+  const bodyless = request.method === 'HEAD' || upstream.status === 304;
+  return new Response(bodyless ? null : upstream.body, {
+    status: upstream.status,
+    statusText: upstream.statusText,
+    headers,
+  });
+}