diff --git a/frontend/src/app/ChatPage.tsx b/frontend/src/app/ChatPage.tsx
index 13651f78..dcce1987 100644
--- a/frontend/src/app/ChatPage.tsx
+++ b/frontend/src/app/ChatPage.tsx
@@ -1544,7 +1544,7 @@ export default function ChatPage() {
   };
 
   return (
-    <div style={{ minHeight: "100dvh", background: "var(--bg)", color: "var(--text)", fontFamily: "system-ui, -apple-system, sans-serif" }}>
+    <div style={{ minHeight: "calc(100dvh - var(--pe-shell-h))", background: "var(--bg)", color: "var(--text)", fontFamily: "system-ui, -apple-system, sans-serif" }}>
       <style>{`
         [data-tip],[data-tip-left],[data-tip-right]{position:relative}
         [data-tip]::after,[data-tip-left]::after,[data-tip-right]::after{
@@ -1580,10 +1580,10 @@ export default function ChatPage() {
         }
       `}</style>
       {/* Body */}
-      <div style={{ display: "flex", margin: "0 auto", padding: "0", gap: "0", width: "100%", minHeight: "100dvh" }}>
+      <div style={{ display: "flex", margin: "0 auto", padding: "0", gap: "0", width: "100%", minHeight: "calc(100dvh - var(--pe-shell-h))" }}>
         {!isEmbed && !sidebarOpen && (
           /* Rail */
-          <div data-pe-sidebar style={{ width: "60px", flexShrink: 0, background: "var(--sidebar-bg)", borderRight: "1px solid var(--border)", display: "flex", flexDirection: "column", alignItems: "center", padding: "10px 0", position: "sticky", top: 0, height: "100dvh", boxSizing: "border-box" }}>
+          <div data-pe-sidebar style={{ width: "60px", flexShrink: 0, background: "var(--sidebar-bg)", borderRight: "1px solid var(--border)", display: "flex", flexDirection: "column", alignItems: "center", padding: "10px 0", position: "sticky", top: "var(--pe-shell-h)", height: "calc(100dvh - var(--pe-shell-h))", boxSizing: "border-box" }}>
             <button onClick={() => setSidebarOpen(true)} data-tip-right="Open sidebar" aria-label="Open sidebar" style={{ background: "transparent", border: "none", cursor: "pointer", padding: "8px", borderRadius: "10px", display: "flex", color: "var(--text)", marginBottom: "4px" }}
               onMouseEnter={(e) => (e.currentTarget as HTMLElement).style.background = "var(--surface-hover)"}
               onMouseLeave={(e) => (e.currentTarget as HTMLElement).style.background = "transparent"}
@@ -1628,7 +1628,7 @@ export default function ChatPage() {
         )}
         {/* Sidebar */}
         {!isEmbed && sidebarOpen && (
-          <div data-pe-sidebar style={{ width: "260px", flexShrink: 0, background: "var(--sidebar-bg)", borderRight: "1px solid var(--border)", padding: "12px 8px", position: "sticky", top: 0, height: "100dvh", alignSelf: "flex-start", display: "flex", flexDirection: "column", boxSizing: "border-box" }}>
+          <div data-pe-sidebar style={{ width: "260px", flexShrink: 0, background: "var(--sidebar-bg)", borderRight: "1px solid var(--border)", padding: "12px 8px", position: "sticky", top: "var(--pe-shell-h)", height: "calc(100dvh - var(--pe-shell-h))", alignSelf: "flex-start", display: "flex", flexDirection: "column", boxSizing: "border-box" }}>
             <div style={{ display: "flex", alignItems: "center", justifyContent: "space-between", marginBottom: "4px", padding: "4px 4px 4px 10px", gap: "8px" }}>
               {/* eslint-disable-next-line @next/next/no-img-element */}
               <img src={`${APP_BASE_PATH}/policyengine-logo.svg`} alt="PolicyEngine" style={{ display: "block", width: "128px", height: "auto" }} />
@@ -1798,7 +1798,7 @@ export default function ChatPage() {
         )}
 
         {/* Chat area */}
-        <div data-pe-chat style={{ flex: 1, padding: "16px 24px max(24px, env(safe-area-inset-bottom))", minWidth: 0, minHeight: "100dvh", boxSizing: "border-box", display: "flex", flexDirection: "column", justifyContent: hasMessages ? "flex-start" : "center", alignItems: "stretch" }}>
+        <div data-pe-chat style={{ flex: 1, padding: "16px 24px max(24px, env(safe-area-inset-bottom))", minWidth: 0, minHeight: "calc(100dvh - var(--pe-shell-h))", boxSizing: "border-box", display: "flex", flexDirection: "column", justifyContent: hasMessages ? "flex-start" : "center", alignItems: "stretch" }}>
           {!hasMessages && (
             <div style={{ width: "100%", maxWidth: "760px", margin: "0 auto", textAlign: "center", marginBottom: "20px" }}>
               <h1 style={{ fontSize: "30px", fontWeight: 500, color: "var(--text)", margin: 0, letterSpacing: "-0.01em" }}>What&apos;s on your mind today?</h1>
diff --git a/frontend/src/app/layout.tsx b/frontend/src/app/layout.tsx
index 239d0a8a..32f42941 100644
--- a/frontend/src/app/layout.tsx
+++ b/frontend/src/app/layout.tsx
@@ -1,6 +1,7 @@
 import type { Metadata, Viewport } from "next";
 import "@mantine/core/styles.css";
 import { APP_BASE_PATH } from "@/utils/backend";
+import SiteHeader from "@/components/SiteHeader";
 import Providers from "./Providers";
 
 export const metadata: Metadata = {
@@ -22,6 +23,10 @@ export const viewport: Viewport = {
 
 const themeVars = `
   :root {
+    /* Height of the PolicyEngine site shell. The chat's full-height panes
+       subtract this so the header does not push them below the fold.
+       SiteHeader sets it to 0px for embedded (?embed) copies. */
+    --pe-shell-h: 56px;
     --bg: #ffffff;
     --surface: #ffffff;
     --surface-2: #f4f4f4;
@@ -88,6 +93,7 @@ export default function RootLayout({ children }: { children: React.ReactNode })
         />
       </head>
       <body style={{ margin: 0, fontFamily: "system-ui, -apple-system, sans-serif", background: "var(--bg)", color: "var(--text)" }}>
+        <SiteHeader />
         <Providers>{children}</Providers>
       </body>
     </html>
diff --git a/frontend/src/components/SiteHeader.tsx b/frontend/src/components/SiteHeader.tsx
new file mode 100644
index 00000000..eb930111
--- /dev/null
+++ b/frontend/src/components/SiteHeader.tsx
@@ -0,0 +1,110 @@
+"use client";
+
+import { useEffect, useState } from "react";
+
+/**
+ * The PolicyEngine site shell.
+ *
+ * /uk/chat is served on policyengine.org through a multizone rewrite, and the
+ * rewrite does not inject the parent app's header into this response — every
+ * zone child renders the shell itself. The app-zone-shell-audit in
+ * policyengine-app-v2 asserts that the top 140px of the page carries the
+ * PolicyEngine brand plus the Research, Model, API and Donate nav labels.
+ *
+ * Links are absolute so they resolve both here and on the standalone
+ * deployment, where /uk/* belongs to the chat rather than the website.
+ */
+const SITE = "https://policyengine.org";
+
+const NAV_LINKS = [
+  { label: "Research", href: `${SITE}/uk/research` },
+  { label: "Model", href: `${SITE}/uk/model` },
+  { label: "API", href: `${SITE}/uk/api` },
+  { label: "About", href: `${SITE}/uk/team` },
+];
+
+export default function SiteHeader() {
+  // Embedded copies (?embed) are framed inside another page that already has
+  // its own chrome, so the shell would be a duplicate header.
+  const [isEmbed, setIsEmbed] = useState(false);
+
+  useEffect(() => {
+    const embedded = new URLSearchParams(window.location.search).has("embed");
+    setIsEmbed(embedded);
+    document.documentElement.style.setProperty(
+      "--pe-shell-h",
+      embedded ? "0px" : "",
+    );
+  }, []);
+
+  if (isEmbed) return null;
+
+  return (
+    <header
+      style={{
+        height: "var(--pe-shell-h)",
+        boxSizing: "border-box",
+        position: "sticky",
+        top: 0,
+        zIndex: 100,
+        background: "var(--bg)",
+        borderBottom: "1px solid var(--border)",
+        display: "flex",
+        alignItems: "center",
+        justifyContent: "space-between",
+        gap: "16px",
+        padding: "0 24px",
+      }}
+    >
+      <a
+        href={`${SITE}/uk`}
+        aria-label="PolicyEngine"
+        style={{
+          display: "flex",
+          alignItems: "center",
+          gap: "8px",
+          textDecoration: "none",
+          color: "var(--text)",
+          fontWeight: 700,
+          letterSpacing: "0.02em",
+          whiteSpace: "nowrap",
+        }}
+      >
+        PolicyEngine
+      </a>
+
+      <nav
+        aria-label="PolicyEngine navigation"
+        style={{
+          display: "flex",
+          alignItems: "center",
+          gap: "20px",
+          fontSize: "14px",
+          whiteSpace: "nowrap",
+        }}
+      >
+        {NAV_LINKS.map((link) => (
+          <a
+            key={link.label}
+            href={link.href}
+            style={{ color: "var(--text-2)", textDecoration: "none" }}
+          >
+            {link.label}
+          </a>
+        ))}
+        <a
+          href={`${SITE}/uk/donate`}
+          style={{
+            color: "var(--text)",
+            textDecoration: "none",
+            border: "1px solid var(--border)",
+            borderRadius: "6px",
+            padding: "6px 14px",
+          }}
+        >
+          Donate
+        </a>
+      </nav>
+    </header>
+  );
+}