fix(web): return a cleanup from the preload-error installer

Review feedback: window is shared across vitest tests, so repeated
installs accumulated listeners. The installer now returns a remover and
the tests detach in afterEach.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

web/src/lib/reloadOnPreloadError.test.ts

@@ -1,4 +1,4 @@
-import { describe, expect, it, vi } from "vitest";
+import { afterEach, describe, expect, it, vi } from "vitest";
 import { installPreloadErrorReload } from "./reloadOnPreloadError";
 
 function harness(now: () => number) {
@@ -16,9 +16,16 @@ function harness(now: () => number) {
 }
 
 describe("installPreloadErrorReload", () => {
+  let cleanups: Array<() => void> = [];
+
+  afterEach(() => {
+    cleanups.forEach((cleanup) => cleanup());
+    cleanups = [];
+  });
+
   it("reloads when a dynamically imported chunk fails to load", () => {
     const { reload, deps } = harness(() => 1_000_000);
-    installPreloadErrorReload(deps);
+    cleanups.push(installPreloadErrorReload(deps));
 
     window.dispatchEvent(new Event("vite:preloadError"));
     expect(reload).toHaveBeenCalledTimes(1);
@@ -28,14 +35,14 @@ describe("installPreloadErrorReload", () => {
     let clock = 1_000_000;
     const { reload, deps } = harness(() => clock);
 
-    installPreloadErrorReload(deps);
+    cleanups.push(installPreloadErrorReload(deps));
     window.dispatchEvent(new Event("vite:preloadError"));
     expect(reload).toHaveBeenCalledTimes(1);
 
     // Post-reload page still hits the error seconds later: give up instead
     // of reload-looping.
     clock += 5_000;
-    installPreloadErrorReload(deps);
+    cleanups.push(installPreloadErrorReload(deps));
     window.dispatchEvent(new Event("vite:preloadError"));
     expect(reload).toHaveBeenCalledTimes(1);
   });
@@ -44,12 +51,12 @@ describe("installPreloadErrorReload", () => {
     let clock = 1_000_000;
     const { reload, deps } = harness(() => clock);
 
-    installPreloadErrorReload(deps);
+    cleanups.push(installPreloadErrorReload(deps));
     window.dispatchEvent(new Event("vite:preloadError"));
     expect(reload).toHaveBeenCalledTimes(1);
 
     clock += 10 * 60_000;
-    installPreloadErrorReload(deps);
+    cleanups.push(installPreloadErrorReload(deps));
     window.dispatchEvent(new Event("vite:preloadError"));
     expect(reload).toHaveBeenCalledTimes(2);
   });

web/src/lib/reloadOnPreloadError.ts

@@ -15,13 +15,13 @@ interface PreloadErrorReloadDeps {
   setItem: (key: string, value: string) => void;
 }
 
-export function installPreloadErrorReload(deps?: Partial<PreloadErrorReloadDeps>): void {
+export function installPreloadErrorReload(deps?: Partial<PreloadErrorReloadDeps>): () => void {
   const reload = deps?.reload ?? (() => window.location.reload());
   const now = deps?.now ?? Date.now;
   const getItem = deps?.getItem ?? ((k: string) => sessionStorage.getItem(k));
   const setItem = deps?.setItem ?? ((k: string, v: string) => sessionStorage.setItem(k, v));
 
-  window.addEventListener("vite:preloadError", (event) => {
+  const handler = (event: Event) => {
     const lastReloadAt = Number(getItem(GUARD_KEY) ?? 0);
     if (now() - lastReloadAt < GUARD_WINDOW_MS) {
       // We already reloaded moments ago and the chunk is still missing;
@@ -31,5 +31,8 @@ export function installPreloadErrorReload(deps?: Partial<PreloadErrorReloadDeps>
     event.preventDefault();
     setItem(GUARD_KEY, String(now()));
     reload();
-  });
+  };
+
+  window.addEventListener("vite:preloadError", handler);
+  return () => window.removeEventListener("vite:preloadError", handler);
 }