diff --git a/tests/browser/workflows.spec.mjs b/tests/browser/workflows.spec.mjs
index 2f31eda..0ee4620 100644
--- a/tests/browser/workflows.spec.mjs
+++ b/tests/browser/workflows.spec.mjs
@@ -74,6 +74,24 @@ test('a page whose leave was called off reads its list again on the next input',
     await expect(page.locator('#resultsTitle')).toHaveText('Recent Prompts');
 });
 
+// The gallery's startup thumbnail check runs a second after load. When that second ends while the page is leaving,
+// the check must start no read: WebKit fails it with "Fetch API cannot load … due to access control checks." and
+// Playwright reports a page error (seen in CI on PR #289). The page clock makes the second end after the leave began.
+for (const leave of ['beforeunload', 'pagehide']) {
+    test(`the gallery startup check starts no read after ${leave}`, async ({ page }) => {
+        await page.clock.install();
+        const statusReads = [];
+        page.on('request', req => { if (req.url().includes('/images/thumbnails/status')) statusReads.push(req.url()); });
+        await page.goto('/prompt_manager/gallery');
+        await expect(page.locator('#galleryGrid .image-item')).toHaveCount(2);
+        await page.evaluate(type => window.dispatchEvent(new Event(type)), leave);
+        await page.clock.runFor(1500);
+        // A read made after the clock ran is listed, so the listener saw every status read.
+        await page.evaluate(() => fetch('/prompt_manager/images/thumbnails/status?probe=1'));
+        expect(statusReads.map(url => new URL(url).search)).toEqual(['?probe=1']);
+    });
+}
+
 test('actual gallery review generates and persists tags for the selected root', async ({ page, request }) => {
     await page.goto('/prompt_manager/gallery');
     await expect(page.locator('#galleryGrid .image-item')).toHaveCount(2);
diff --git a/tests/js/gallery-thumbnails.test.js b/tests/js/gallery-thumbnails.test.js
index 431beea..5b085f2 100644
--- a/tests/js/gallery-thumbnails.test.js
+++ b/tests/js/gallery-thumbnails.test.js
@@ -73,6 +73,28 @@ test('Not Now persists the collection state and suppresses the unchanged prompt'
     assert.equal(f.prompts.length, 1);
 });
 
+// WebKit fails a fetch a leaving page starts ("Fetch API cannot load … due to access control checks.") and logs it
+// as a page error: the delayed startup check starts no read once the page has begun to leave (as admin.js, #290).
+test('the startup check starts no read once the page is leaving', async () => {
+    const f = fixture({ success: true, total_images: 100, pending: 30, collection_id: 'a' });
+    f.manager.pageLifetime = new AbortController();
+    f.manager.pageLifetime.abort();
+    await f.check();
+    assert.equal(f.requests.length, 0);
+    assert.equal(f.prompts.length, 0);
+});
+
+test('the startup check passes the page lifetime to its read', async () => {
+    const f = fixture({ success: true, total_images: 100, pending: 30, collection_id: 'a' });
+    const signals = [];
+    f.manager.pageLifetime = new AbortController();
+    const get = f.manager.api.get;
+    f.manager.api.get = async (url, options) => { signals.push(options?.signal); return get(url); };
+    await f.check();
+    assert.deepEqual(signals, [f.manager.pageLifetime.signal]);
+    assert.equal(f.prompts.length, 1);
+});
+
 test('disabled checks do not request collection status', async () => {
     const f = fixture({}, { checkThumbnailsAtStartup: false });
     await f.check();
diff --git a/web/js/gallery.js b/web/js/gallery.js
index 7f6b2d6..ee9f24b 100644
--- a/web/js/gallery.js
+++ b/web/js/gallery.js
@@ -17,6 +17,14 @@
                 this.dupResults = null;
 
                 this.api = ApiClient.createApiClient();
+                // The page's lifetime ends when it starts to leave: WebKit fails a fetch a leaving page starts
+                // ("Fetch API cannot load … due to access control checks.") and logs it as a page error.
+                this.pageLifetime = new AbortController();
+                window.addEventListener("beforeunload", () => this.pageLifetime.abort());
+                window.addEventListener("pagehide", () => this.pageLifetime.abort());
+                window.addEventListener("pageshow", (e) => {
+                    if (e.persisted && this.pageLifetime.signal.aborted) this.pageLifetime = new AbortController();
+                });
                 // Only the newest page request may update the grid
                 this.imagesRequest = ApiClient.latestOnly();
 
@@ -2534,8 +2542,11 @@ Seed: ${this.currentMetadata.seed || 'Unknown'}`;
                         return;
                     }
                     
+                    // A leaving page starts no read, and one it aborts is not reported.
+                    const signal = this.pageLifetime?.signal;
+                    if (signal?.aborted) return;
                     try {
-                        const data = await this.api.get('/prompt_manager/images/thumbnails/status');
+                        const data = await this.api.get('/prompt_manager/images/thumbnails/status', { signal });
                         const total = data.total_images;
                         const pending = data.pending;
                         if (!data.success || !Number.isSafeInteger(total) ||