2 files changed, 65 insertions, 29 deletions

diff --git a/frontend-vanilla/src/main.ts b/frontend-vanilla/src/main.ts
index aa00bd3..6a605c4 100644
--- a/frontend-vanilla/src/main.ts
+++ b/frontend-vanilla/src/main.ts
@@ -271,31 +271,17 @@ export function renderItems() {
   if (scrollRoot) {
     let readTimeoutId: number | null = null;
     scrollRoot.onscroll = () => {
-      // Infinite scroll: check immediately on every scroll event (cheap comparison).
-      // Guard: only when content actually overflows the container (scrollHeight > clientHeight).
+      // Infinite scroll check (container only)
       if (!store.loading && store.hasMore && scrollRoot.scrollHeight > scrollRoot.clientHeight) {
         if (scrollRoot.scrollHeight - scrollRoot.scrollTop - scrollRoot.clientHeight < 200) {
           loadMore();
         }
       }
 
-      // Mark-as-read: debounced to avoid excessive DOM queries
+      // Mark-as-read: debounced
       if (readTimeoutId === null) {
         readTimeoutId = window.setTimeout(() => {
-          const containerRect = scrollRoot.getBoundingClientRect();
-
-          store.items.forEach((item) => {
-            if (item.read) return;
-
-            const el = document.querySelector(`.feed-item[data-id="${item._id}"]`);
-            if (el) {
-              const rect = el.getBoundingClientRect();
-              // Mark as read if the bottom of the item is above the top of the container
-              if (rect.bottom < containerRect.top) {
-                updateItem(item._id, { read: true });
-              }
-            }
-          });
+          checkReadItems(scrollRoot);
           readTimeoutId = null;
         }, 250);
       }
@@ -303,6 +289,22 @@ export function renderItems() {
   }
 }
 
+function checkReadItems(scrollRoot: HTMLElement) {
+  const containerRect = scrollRoot.getBoundingClientRect();
+  store.items.forEach((item) => {
+    if (item.read) return;
+
+    const el = document.querySelector(`.feed-item[data-id="${item._id}"]`);
+    if (el) {
+      const rect = el.getBoundingClientRect();
+      // Mark as read if the bottom of the item is above the top of the container
+      if (rect.bottom < containerRect.top) {
+        updateItem(item._id, { read: true });
+      }
+    }
+  });
+}
+
 // Polling fallback for infinite scroll (matches V1 behavior)
 // This ensures that even if scroll events are missed or layout shifts occur without scroll,
 // we still load more items when near the bottom.
@@ -319,18 +321,8 @@ if (typeof window !== 'undefined') {
     if (store.loading || !store.hasMore) return;
 
     if (scrollRoot) {
-      // DEBUG LOGGING
-      /*
-      console.log('Scroll Poll', { 
-          scrollHeight: scrollRoot.scrollHeight, 
-          scrollTop: scrollRoot.scrollTop, 
-          clientHeight: scrollRoot.clientHeight,
-          offset: scrollRoot.scrollHeight - scrollRoot.scrollTop - scrollRoot.clientHeight,
-          docHeight: document.documentElement.scrollHeight,
-          winHeight: window.innerHeight,
-          winScroll: window.scrollY
-      });
-      */
+      // Check for read items periodically (robustness fallback)
+      checkReadItems(scrollRoot);
 
       // Check container scroll (if container is scrollable)
       if (scrollRoot.scrollHeight > scrollRoot.clientHeight) {
diff --git a/frontend-vanilla/src/regression.test.ts b/frontend-vanilla/src/regression.test.ts
index 813e4bb..0c10d95 100644
--- a/frontend-vanilla/src/regression.test.ts
+++ b/frontend-vanilla/src/regression.test.ts
@@ -167,6 +167,50 @@ describe('Scroll-to-Read Regression Tests', () => {
         // API should NOT be called
         expect(apiFetch).not.toHaveBeenCalledWith(expect.stringContaining('/api/item/888'), expect.anything());
     });
+
+    it('should mark item as read when WINDOW scrolls (robustness fallback)', async () => {
+        vi.useRealTimers();
+        const mockItem = {
+            _id: 12345,
+            title: 'Window Scroll Item',
+            read: false,
+            url: 'http://example.com/window',
+            publish_date: '2023-01-01'
+        } as any;
+
+        store.setItems([mockItem]);
+        renderItems();
+
+        // Setup successful detection scenario
+        const mainContent = document.getElementById('main-content');
+        if (mainContent) {
+            mainContent.getBoundingClientRect = vi.fn(() => ({
+                top: 0, bottom: 800, height: 800, left: 0, right: 0, width: 0, x: 0, y: 0, toJSON: () => { }
+            }));
+        }
+
+        const itemEl = document.querySelector(`.feed-item[data-id="12345"]`);
+        if (itemEl) {
+            // Fully scrolled past
+            itemEl.getBoundingClientRect = vi.fn(() => ({
+                top: -150, bottom: -50, height: 100, left: 0, right: 0, width: 0, x: 0, y: 0, toJSON: () => { }
+            }));
+        }
+
+        vi.mocked(apiFetch).mockResolvedValue({ ok: true } as Response);
+
+        // Dispatch scroll on WINDOW, not mainContent
+        window.dispatchEvent(new Event('scroll'));
+
+        // Wait for potential debounce/poll
+        await new Promise(resolve => setTimeout(resolve, 1100));
+
+        // Expect it to handle it
+        expect(apiFetch).toHaveBeenCalledWith(expect.stringContaining('/api/item/12345'), expect.objectContaining({
+            method: 'PUT',
+            body: expect.stringContaining('"read":true')
+        }));
+    });
 });
 
 // NK-t8qnrh: Links in feed item descriptions should have no underlines (match v1 style)