diff --git a/public/sw.js b/public/sw.js
index aff8dc2..cf74ce9 100644
--- a/public/sw.js
+++ b/public/sw.js
@@ -1,7 +1,7 @@
 // Tchatou service worker — installable PWA + offline app shell.
 // Scope: /app/. Only handles same-origin /app/ GETs; the IRC websocket and all
 // API calls (cloudflare, change_password, upload) pass straight through.
-const CACHE = 'tchatou-v53';
+const CACHE = 'tchatou-v54';
 const SHELL = ['/app/', '/app/index.html', '/app/favicon.svg', '/app/orbit-icon.svg', '/app/manifest.webmanifest'];
 
 self.addEventListener('install', (e) => {
diff --git a/src/index.css b/src/index.css
index d2f7890..a34627c 100644
--- a/src/index.css
+++ b/src/index.css
@@ -1695,3 +1695,14 @@ input:focus-visible, textarea:focus-visible, select:focus-visible {
   background: var(--green); color: #fff; padding: .6rem 1rem; border-radius: 0 0 12px 12px;
   font-weight: 600; text-decoration: none; transition: top .15s ease; }
 .skip-link:focus { top: 0; }
+
+/* ── Large-channel virtualization (browser-native) ──────────────────────────
+   Member rows skip layout & paint while off-screen, so a 2,000-member panel
+   only does real rendering work for the handful of visible rows — the rest cost
+   ~nothing until scrolled into view. contain-intrinsic-size gives off-screen
+   rows a placeholder height (so the scrollbar is right); `auto` makes the
+   browser remember each row's real height after it first renders. Visible rows
+   render exactly as before, so small channels are unchanged. Degrades to normal
+   rendering on browsers without content-visibility. */
+.member { content-visibility: auto; contain-intrinsic-size: auto 44px; }
+[data-theme^="yomirc"] .member { contain-intrinsic-size: auto 20px; }