diff --git a/public/nook/og.png b/public/nook/og.png
new file mode 100644
index 0000000..2c308ce
Binary files /dev/null and b/public/nook/og.png differ
diff --git a/src/components/PageHead.test.ts b/src/components/PageHead.test.ts
index 0dd39f1..c9f6855 100644
--- a/src/components/PageHead.test.ts
+++ b/src/components/PageHead.test.ts
@@ -132,12 +132,17 @@ describe("resolvePageHeadMeta — canonical URL derivation", () => {
 });
 
 describe("resolvePageHeadMeta — OpenGraph fallbacks", () => {
-  it("ogImage defaults to the site's ogDefaultImage when not provided", () => {
+  it("ogImage defaults to the site's ogDefaultImage, resolved to an absolute URL", () => {
     const meta = resolvePageHeadMeta(BASE_PROPS, SITE_CONFIG.nessa, "/");
-    expect(meta.ogImage).toBe(SITE_CONFIG.nessa.ogDefaultImage);
+    expect(meta.ogImage).toBe("https://nessa.freno.me/nessa/og-default.png");
   });
 
-  it("explicit ogImage overrides the site default", () => {
+  it("the nook default resolves to the absolute og.png URL", () => {
+    const meta = resolvePageHeadMeta(BASE_PROPS, SITE_CONFIG.nook, "/");
+    expect(meta.ogImage).toBe("https://nook.freno.me/nook/og.png");
+  });
+
+  it("explicit absolute ogImage passes through unchanged", () => {
     const meta = resolvePageHeadMeta(
       { ...BASE_PROPS, ogImage: "https://cdn/custom.png" },
       SITE_CONFIG.main,
@@ -146,6 +151,15 @@ describe("resolvePageHeadMeta — OpenGraph fallbacks", () => {
     expect(meta.ogImage).toBe("https://cdn/custom.png");
   });
 
+  it("explicit site-relative ogImage is resolved against the site domain", () => {
+    const meta = resolvePageHeadMeta(
+      { ...BASE_PROPS, ogImage: "/og/custom.png" },
+      SITE_CONFIG.gaze,
+      "/"
+    );
+    expect(meta.ogImage).toBe("https://gaze.freno.me/og/custom.png");
+  });
+
   it("ogTitle falls back to the base title (no suffix)", () => {
     const meta = resolvePageHeadMeta(BASE_PROPS, SITE_CONFIG.main, "/");
     expect(meta.ogTitle).toBe("Blog");
diff --git a/src/components/PageHead.tsx b/src/components/PageHead.tsx
index 5a050b5..5ff623d 100644
--- a/src/components/PageHead.tsx
+++ b/src/components/PageHead.tsx
@@ -56,6 +56,8 @@ export default function PageHead(props: PageHeadProps) {
         <Meta property="og:description" content={meta().ogDescription} />
       )}
       <Meta property="og:image" content={meta().ogImage} />
+      {/* X/Twitter large-image card; falls back to the og:* tags above. */}
+      <Meta name="twitter:card" content="summary_large_image" />
     </>
   );
 }
diff --git a/src/components/page-head-meta.ts b/src/components/page-head-meta.ts
index 4990130..a824a73 100644
--- a/src/components/page-head-meta.ts
+++ b/src/components/page-head-meta.ts
@@ -16,6 +16,9 @@
  *    prefix-strip below also handles any legacy prefixed form, so the canonical
  *    is always the public URL.
  *  - `ogImage` → explicit `props.ogImage` wins; otherwise `site.ogDefaultImage`.
+ *    Either way it is resolved to an **absolute** URL against the site's
+ *    domain — OG consumers (X, Slack, Discord, iMessage) require an absolute
+ *    URL, and a site-relative path in `ogDefaultImage` would 404 otherwise.
  *  - `ogTitle` / `ogDescription` → explicit override wins; otherwise fall
  *    back to the base title (no suffix) / description (existing behavior).
  */
@@ -49,6 +52,20 @@ export interface ResolvedPageHeadMeta {
   ogImage: string;
 }
 
+/**
+ * Resolve an OpenGraph image reference to an absolute URL.
+ *
+ * OG consumers (X, Slack, Discord, LinkedIn, iMessage) require an absolute
+ * URL; `ogDefaultImage` values are site-relative paths (`/nook/og.png`), so
+ * they are joined to the site origin here. Already-absolute references
+ * (`https:`, `data:`, protocol-relative `//`) pass through untouched.
+ */
+function absolutizeOgImage(image: string, domain: string): string {
+  if (image.startsWith("//")) return `https:${image}`;
+  if (/^[a-z][a-z0-9+.-]*:/i.test(image)) return image;
+  return `https://${domain}${image.startsWith("/") ? "" : "/"}${image}`;
+}
+
 export function resolvePageHeadMeta(
   props: PageHeadProps,
   site: Site,
@@ -71,7 +88,10 @@ export function resolvePageHeadMeta(
   const canonical = props.canonical ?? `https://${site.domain}${publicPath}`;
   const ogTitle = props.ogTitle ?? props.title;
   const ogDescription = props.ogDescription ?? props.description;
-  const ogImage = props.ogImage ?? site.ogDefaultImage;
+  const ogImage = absolutizeOgImage(
+    props.ogImage ?? site.ogDefaultImage,
+    site.domain
+  );
 
   return {
     title,
diff --git a/src/lib/site-context.ts b/src/lib/site-context.ts
index 1a894bd..1480c3a 100644
--- a/src/lib/site-context.ts
+++ b/src/lib/site-context.ts
@@ -132,7 +132,7 @@ export const SITE_CONFIG: Record<SiteId, Site> = {
     titleSuffix: " | The Nook",
     brandColor: "#4C9FBC",
     brandColorDark: "#4C9FBC",
-    ogDefaultImage: "/nook/og-default.png",
+    ogDefaultImage: "/nook/og.png",
     faviconPath: "/nook/favicon/favicon.ico"
   }
 };
diff --git a/src/routes/nessa/meta.test.ts b/src/routes/nessa/meta.test.ts
index 0b4b42e..e04c898 100644
--- a/src/routes/nessa/meta.test.ts
+++ b/src/routes/nessa/meta.test.ts
@@ -40,13 +40,13 @@ describe("Nessa landing page — PageHead metadata", () => {
     expect(meta.canonical).toBe("https://nessa.freno.me/");
   });
 
-  it("ogImage falls back to the nessa site default", () => {
+  it("ogImage falls back to the nessa site default, resolved absolute", () => {
     const meta = resolvePageHeadMeta(
       NESSA_LANDING_META,
       SITE_CONFIG.nessa,
       "/"
     );
-    expect(meta.ogImage).toBe(SITE_CONFIG.nessa.ogDefaultImage);
+    expect(meta.ogImage).toBe("https://nessa.freno.me/nessa/og-default.png");
   });
 
   it("ogTitle uses the explicit marketing copy, not the bare title", () => {
diff --git a/src/routes/nook/index.tsx b/src/routes/nook/index.tsx
index d774865..87c4a50 100644
--- a/src/routes/nook/index.tsx
+++ b/src/routes/nook/index.tsx
@@ -57,7 +57,7 @@ export default function NookLanding() {
       <PageHead
         title="Home"
         description="The Nook — a native macOS utility for coding-agent orchestration, fan and thermal control."
-        ogImage="/nook/og-default.png"
+        ogImage={`https://${site().domain}/nook/og.png`}
         ogTitle="The Nook — native macOS agent orchestration"
         ogDescription="A one-time-purchase macOS app for coding-agent orchestration, fan control, and thermal insight."
       />