test(e2e): assert static assets resolve under a custom base path (#4880)

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

e2e/custom.spec.ts

@@ -1,7 +1,10 @@
 import { test, expect } from "@playwright/test";
 
+const origin = "http://custom_base:8080";
+const base = "/foobarbase";
+
 test.beforeEach(async ({ page }) => {
-  await page.goto("http://custom_base:8080/foobarbase");
+  await page.goto(origin + base);
 });
 
 test("has right title", async ({ page }) => {
@@ -11,3 +14,35 @@ test("has right title", async ({ page }) => {
 test("url should have custom base", async ({ page }) => {
   await expect(page).toHaveURL(/foobarbase/);
 });
+
+test("static assets resolve under the custom base", async ({ page }) => {
+  const requested: string[] = [];
+  const broken: string[] = [];
+
+  const isAsset = (url: string) => new URL(url).pathname.includes("/assets/");
+
+  page.on("request", (request) => {
+    if (isAsset(request.url())) requested.push(new URL(request.url()).pathname);
+  });
+  page.on("response", (response) => {
+    if (isAsset(response.url()) && response.status() >= 400) {
+      broken.push(`${response.status()} ${response.url()}`);
+    }
+  });
+
+  await page.reload();
+  await expect(page).toHaveTitle(/.* - Dozzle/);
+  // fonts are only fetched when a glyph needs them, so force the @font-face src to resolve.
+  // swallow the rejection on a bad url so the assertions below report which path was wrong
+  await page.evaluate(() =>
+    document.fonts.load('400 1rem "JetBrains Mono"').then(
+      () => {},
+      () => {},
+    ),
+  );
+
+  // the css lives at <base>/assets/, so a relative url() in it must resolve back under <base>
+  expect(requested.some((path) => path.endsWith(".woff2"))).toBe(true);
+  expect(requested.filter((path) => !path.startsWith(`${base}/assets/`))).toEqual([]);
+  expect(broken).toEqual([]);
+});