diff --git a/frontend/taskdeck-web/tests/e2e/pwa-proof-strict.spec.ts b/frontend/taskdeck-web/tests/e2e/pwa-proof-strict.spec.ts
index f4e5dec5d..12792309e 100644
--- a/frontend/taskdeck-web/tests/e2e/pwa-proof-strict.spec.ts
+++ b/frontend/taskdeck-web/tests/e2e/pwa-proof-strict.spec.ts
@@ -139,3 +139,193 @@ test('old #2350 worker -> v2 controller, static cache invalidated, share queue p
     await context.close()
   }
 })
+
+/*
+ * #2475 - the install-to-activation re-poisoning window, at browser level.
+ *
+ * public/api-cache-cleanup.js sweeps the runtime caches twice: once at script evaluation
+ * (which happens while the replacement is INSTALLING, so the old vulnerable worker still
+ * controls every open page) and once inside `event.waitUntil` on activate with
+ * `force: true`. Only the second pass can remove something the old worker cached after the
+ * first one finished, which is exactly the window this case pins.
+ *
+ * The window is held open by the browser rather than raced. `registerType: 'prompt'` parks a
+ * replacement that has finished installing in `waiting` until a page sends
+ * `taskdeck:skip-waiting`, and the real sign-in migration is what sends it. So the seed lands
+ * strictly after the install-time sweep (proven by the marker cache that sweep writes last)
+ * and strictly before activation (proven by `registration.waiting` and by the old worker
+ * still answering the pre-#2350 policy handshake).
+ *
+ * The seed is written by the OLD worker's own CacheFirst handler, from a real network
+ * response, not by page script reaching into CacheStorage.
+ */
+test('a static entry the old worker caches between install and activation does not survive the migration', async ({ browser, request }) => {
+  // EXPECTED FAILURE (#2475). This case is red against the current production build and is
+  // marked so the pwa-proof lane keeps a meaningful green/red verdict for the strict case
+  // above. The final assertion fails because the forced activate-time re-sweep described in
+  // the header never runs on the generated worker: public/api-cache-cleanup.js (see the
+  // comment at its end, landed with #2416) records that its `activate` listener is attached
+  // from inside vite-plugin-pwa's asynchronous AMD factory, after the activate event has
+  // already been dispatched, so only the memoised evaluation-time sweep ever fires and it has
+  // already resolved by the time this case seeds. The seed therefore survives the migration.
+  // When the production repair lands (an activation hook that registers synchronously, or the
+  // injectManifest move), this case starts passing and Playwright reports "expected to fail
+  // but passed": remove this modifier then. Nothing in CI runs this file, so the marker only
+  // governs the manually driven lane.
+  test.fail()
+
+  const account = await registerUserSession(request, 'pwa-proof-race')
+  const context = await browser.newContext({ serviceWorkers: 'allow' })
+  const page = await context.newPage()
+
+  // A real precached asset plus a marker query: the response is a genuine 200 the old
+  // CacheFirst rule admits, and the query keeps the seeded entry distinguishable from the
+  // icons the app itself fetches.
+  const seedPath = '/icons/icon-192x192.png?td-race-seed=1'
+
+  let serveLegacyWorker = true
+  await context.route('**/sw.js', async (route) => {
+    if (!serveLegacyWorker) {
+      await route.fallback()
+      return
+    }
+    serveLegacyWorker = false
+    await route.fulfill({
+      contentType: 'text/javascript',
+      body: [
+        "self.addEventListener('message', (event) => { if (event.data?.type === 'taskdeck:api-cache-policy' && event.ports?.[0]) event.ports[0].postMessage({ policy: 'legacy-api-cache-retired' }) })",
+        "self.addEventListener('install', () => self.skipWaiting())",
+        "self.addEventListener('activate', (event) => event.waitUntil(self.clients.claim()))",
+        // The pre-#2350 static-asset route: matched on file extension alone, CacheFirst into
+        // the shared taskdeck-static-assets runtime cache. This is the handler whose writes
+        // the migration has to invalidate.
+        "self.addEventListener('fetch', (event) => {",
+        "  if (event.request.method !== 'GET') return",
+        "  if (!/\\.(png|svg|webp|ico|woff2?)$/.test(new URL(event.request.url).pathname)) return",
+        '  event.respondWith((async () => {',
+        "    const cache = await caches.open('taskdeck-static-assets')",
+        '    const hit = await cache.match(event.request)',
+        '    if (hit) return hit',
+        '    const response = await fetch(event.request)',
+        '    if (response.status === 200) await cache.put(event.request, response.clone())',
+        '    return response',
+        '  })())',
+        '})',
+      ].join('\n'),
+    })
+  })
+
+  const askPolicy = () => page.evaluate(() => new Promise<string | null>((resolve) => {
+    const controller = navigator.serviceWorker.controller
+    if (!controller) { resolve(null); return }
+    const channel = new MessageChannel()
+    const timer = setTimeout(() => resolve('__timeout__'), 2_000)
+    channel.port1.onmessage = (event) => {
+      clearTimeout(timer)
+      resolve((event.data as { policy?: string }).policy ?? '__nopolicy__')
+    }
+    controller.postMessage({ type: 'taskdeck:api-cache-policy' }, [channel.port2])
+  }))
+
+  const staticEntries = () => page.evaluate(async () =>
+    (await (await caches.open('taskdeck-static-assets')).keys()).map((r) => r.url))
+
+  try {
+    await page.goto('/login')
+    await page.evaluate(async () => {
+      await navigator.serviceWorker.register('/sw.js')
+      await navigator.serviceWorker.ready
+    })
+    await expect.poll(() => page.evaluate(() => navigator.serviceWorker.controller !== null)).toBe(true)
+    expect(await askPolicy()).toBe('legacy-api-cache-retired')
+
+    // Bring the replacement all the way to `waiting`. It cannot activate from there without
+    // the page's skip-waiting message, so the rest of this case runs inside a window the
+    // browser holds open instead of one measured against a clock.
+    const replacementState = await page.evaluate(() => new Promise<string>((resolve) => {
+      void (async () => {
+        const registration = await navigator.serviceWorker.getRegistration()
+        if (!registration) { resolve('__noregistration__'); return }
+        let settled = false
+        const settle = (value: string) => {
+          if (settled) return
+          settled = true
+          clearTimeout(timer)
+          resolve(value)
+        }
+        const timer = setTimeout(() => settle('__timeout__'), 30_000)
+        const follow = (worker: ServiceWorker | null) => {
+          if (!worker) return
+          if (worker.state !== 'installing') { settle(worker.state); return }
+          worker.addEventListener('statechange', () => {
+            if (worker.state !== 'installing') settle(worker.state)
+          })
+        }
+        registration.addEventListener('updatefound', () => follow(registration.installing))
+        if (registration.waiting) { settle('installed'); return }
+        follow(registration.installing)
+        try {
+          await registration.update()
+        } catch {
+          settle('__updatefailed__')
+        }
+      })()
+    }))
+    console.log('PROOF raceReplacementState =', replacementState)
+    // 'installed' is the waiting state: installed, not activated, activation withheld.
+    expect(replacementState).toBe('installed')
+
+    // The install-time sweep writes the marker cache last, so its presence proves that sweep
+    // completed. Anything seeded from here on is strictly inside the window under test.
+    await expect.poll(
+      () => page.evaluate(() => caches.has('taskdeck-pwa-cache-policy-v2')),
+      { timeout: 15_000 },
+    ).toBe(true)
+
+    const windowOpen = await page.evaluate(async () => {
+      const registration = await navigator.serviceWorker.getRegistration()
+      return {
+        waiting: Boolean(registration?.waiting),
+        activeState: registration?.active?.state ?? null,
+        controllerPresent: navigator.serviceWorker.controller !== null,
+      }
+    })
+    console.log('PROOF raceWindowOpen =', JSON.stringify(windowOpen))
+    expect(windowOpen.waiting).toBe(true)
+    expect(windowOpen.controllerPresent).toBe(true)
+    // Still the pre-#2350 worker: the replacement has not taken over yet.
+    expect(await askPolicy()).toBe('legacy-api-cache-retired')
+
+    // Seed through the OLD worker's CacheFirst handler. Its `cache.put` is awaited before the
+    // response is returned, so this fetch resolving means the entry is already stored.
+    const seedStatus = await page.evaluate(async (path) => (await fetch(path)).status, seedPath)
+    expect(seedStatus).toBe(200)
+    const seededEntries = await staticEntries()
+    console.log('PROOF raceSeededEntries =', JSON.stringify(seededEntries))
+    expect(seededEntries.some((u) => u.includes('td-race-seed'))).toBe(true)
+
+    // The window is still open after the seed: the replacement is still waiting and the old
+    // worker is still the controller, so the entry was written before activation.
+    const windowStillOpen = await page.evaluate(async () =>
+      Boolean((await navigator.serviceWorker.getRegistration())?.waiting))
+    expect(windowStillOpen).toBe(true)
+    expect(await askPolicy()).toBe('legacy-api-cache-retired')
+
+    // Real migration: sign-in runs retireLegacyApiCacheWorker(), which sends skip-waiting to
+    // the waiting worker and lets it activate.
+    await page.getByLabel('Username or Email').fill(account.user.username)
+    await page.getByLabel('Password').fill('E2ePassword123!')
+    await page.getByRole('button', { name: 'Sign in' }).click()
+    await page.waitForURL('**/workspace/home')
+    await expect.poll(askPolicy, { timeout: 20_000 }).toBe('taskdeck-api-cache-policy-v2')
+
+    const entriesAfter = await staticEntries()
+    console.log('PROOF raceEntriesAfter =', JSON.stringify(entriesAfter))
+    console.log('PROOF raceKeysAfter =', JSON.stringify(await page.evaluate(() => caches.keys())))
+    // Only the forced re-sweep inside the activate handler can remove this: the memoised
+    // evaluation-time sweep already resolved and its marker cache is already present.
+    expect(entriesAfter.some((u) => u.includes('td-race-seed'))).toBe(false)
+  } finally {
+    await context.close()
+  }
+})