Reapply "chromium"

This reverts commit 5b85f5de2e.

public/s/js/f0ckm.js

@@ -184,7 +184,16 @@ window.cancelAnimFrame = (function () {
         return;
     }
 
-    if (!lazyObserver) {
+    // Chromium fix: always disconnect the old observer before creating a new one.
+    // Chromium holds detached DOM nodes in an IntersectionObserver alive much longer
+    // than Firefox does. If we reuse a stale observer after an AJAX content swap,
+    // Chromium can fire callbacks for old detached nodes, causing duplicate image
+    // fetches and flooding the network. Disconnecting releases those references.
+    if (lazyObserver) {
+        lazyObserver.disconnect();
+        lazyObserver = null;
+    }
+
     lazyObserver = new IntersectionObserver((entries) => {
         entries.forEach(entry => {
             if (entry.isIntersecting) {
@@ -237,7 +246,6 @@ window.cancelAnimFrame = (function () {
             }
         });
     }, { rootMargin: '300px 0px', threshold: 0.01 });
-    }
 
     // Nudge lazy loading on tab switch to prevent stuck skeletons in inactive tabs
     if (!window._lazyVisibilityBound) {
@@ -254,7 +262,10 @@ window.cancelAnimFrame = (function () {
     }
 
     document.querySelectorAll('.lazy-thumb').forEach(thumb => {
-        if (!thumb.dataset.lazyObserved) {
+        // Reset lazyObserved on every initLazyLoading call so the fresh observer
+        // picks up all unloaded thumbs regardless of previous observation state.
+        delete thumb.dataset.lazyObserved;
+        if (!thumb.classList.contains('loaded')) {
             thumb.dataset.lazyObserved = 'true';
             lazyObserver.observe(thumb);
         }

src/index.mjs

@@ -535,6 +535,17 @@ process.on('uncaughtException', err => {
         }
         return;
       }
+      // Thumbnails (/t/) and covers (/ca/) are static WebP files that never change at a
+      // given URL — the client appends a ?t= cache-bust param when a thumb is regenerated.
+      // Without an explicit Cache-Control header, Chromium treats these as uncacheable and
+      // re-fetches every visible thumbnail on every AJAX navigation, causing severe lag.
+      // Firefox uses a more lenient heuristic and caches them anyway — hence the difference.
+      if (req.url.pathname.match(/^\/(t|ca)\//)) {
+        res.setHeader('Cache-Control', 'public, max-age=31536000, immutable');
+      } else if (req.url.pathname.match(/^\/(b|a|memes)\//)) {
+        // Full-size images and avatars: cache for 1 hour, re-validate after
+        res.setHeader('Cache-Control', 'public, max-age=3600');
+      }
       return;
     }
     const availableThemes = cfg.websrv.themes || ['amoled', 'atmos', 'f0ck', 'f0ck95d', 'iced', 'orange', 'p1nk', '4d'];