diff --git a/src/app/globals.css b/src/app/globals.css
index 6a6bda59..b0c43984 100644
--- a/src/app/globals.css
+++ b/src/app/globals.css
@@ -338,3 +338,17 @@ html {
 html {
   overflow-x: clip;
 }
+
+/* iOS in-app WebView (Telegram, Instagram, Facebook, Twitter, TikTok)
+   downgrade only: drop sticky on the site header so the iOS 26 WebKit
+   jitter bug (bugs.webkit.org/297779) cannot expose a gap at the top.
+   The `ios-webview` class is set by an inline script in layout.tsx
+   based on userAgent (iOS device with no `Safari/` token = WebView).
+   Regular mobile Safari / Chrome iOS keep sticky because the symptom
+   does not visibly trigger there. Desktop is sticky everywhere. */
+@media (max-width: 767px) {
+  html.ios-webview .site-header-root {
+    position: relative;
+    top: auto;
+  }
+}
diff --git a/src/app/layout.tsx b/src/app/layout.tsx
index 6ae2e892..84324b72 100644
--- a/src/app/layout.tsx
+++ b/src/app/layout.tsx
@@ -124,6 +124,18 @@ export default function RootLayout({
             __html: `(function(){try{var t=localStorage.getItem('ocb-theme');var d=t==='dark'||(!t&&window.matchMedia('(prefers-color-scheme: dark)').matches);if(d)document.documentElement.classList.add('dark');}catch(e){}})();`,
           }}
         />
+        {/* Detect iOS in-app WebView (Telegram, Instagram, FB, Twitter, etc.).
+            These hosts hit the iOS 26 WebKit fixed/sticky jitter bug
+            (bugs.webkit.org/297779) harder than regular Safari because their
+            own URL-bar overlay animates the layout viewport on top of the
+            WebKit regression. CSS below downgrades the site header to
+            non-sticky only when this class is present. Inline so the class
+            is on the html element before React hydrates — no flash. */}
+        <script
+          dangerouslySetInnerHTML={{
+            __html: `(function(){try{var ua=navigator.userAgent;if(/iPhone|iPad|iPod/.test(ua)&&!/Safari\\//.test(ua))document.documentElement.classList.add('ios-webview');}catch(e){}})();`,
+          }}
+        />
       </head>
       {/* grid (not flex) so position: sticky on <SiteHeader> works reliably
           on iOS Safari — sticky inside a flex column has known quirks.
diff --git a/src/components/site-header.tsx b/src/components/site-header.tsx
index 153c9d3d..f238c6c1 100644
--- a/src/components/site-header.tsx
+++ b/src/components/site-header.tsx
@@ -39,16 +39,14 @@ export function SiteHeader() {
 
   return (
     <div
-      // Sticky only on md+ (desktop). On mobile the header stays in normal
-      // flow and scrolls away with the page. Reason: WebKit iOS 26 has a
-      // regression (bugs.webkit.org/297779) where sticky AND fixed elements
-      // jitter 10-24 px on scroll direction change, leaving a visible gap
-      // at the top in every WKWebView host (Telegram in-app, Chrome iOS,
-      // Mastodon and LinkedIn ship the same symptom). Apple's fix is
-      // partial; until iOS 26.2+ lands across the user base, non-sticky on
-      // mobile is the only way to avoid the jitter entirely. Standard
-      // mobile UX anyway — pull to top to see the nav.
-      className="relative md:sticky md:top-0 z-50 flex flex-col font-sans bg-surface"
+      // Sticky everywhere by default. Only iOS in-app WebViews (Telegram,
+      // Instagram, FB, etc.) get downgraded to non-sticky to dodge the
+      // iOS 26 WebKit jitter bug (bugs.webkit.org/297779). Regular mobile
+      // Safari and Chrome iOS keep their sticky nav because the symptom is
+      // not visible there in practice. Override lives in globals.css
+      // (`html.ios-webview .site-header-root` rule) so the WebView-only
+      // selector stays out of the Tailwind class soup here.
+      className="site-header-root sticky top-0 z-50 flex flex-col font-sans bg-surface"
     >
       <header className="border-b border-rule py-4 md:py-5 px-4 sm:px-6 shrink-0 text-sm bg-surface relative">
         <div className="max-w-[1400px] mx-auto flex items-center justify-between gap-3">