Use parent domain to set gitbook visitor cookie (#814)

* Use parent domain to set gitbook visitor cookie

* changeset

Author: taranvohra

.changeset/red-kings-sniff.md

@@ -0,0 +1,5 @@
+---
+'@gitbook/adaptive': patch
+---
+
+Use parent domain to set gitbook visitor cookie

packages/adaptive/src/bucket.ts

@@ -16,7 +16,7 @@ export function withBucket(client: BucketClient): () => void {
             features[key] = enabled;
         }
 
-        writeGitBookVisitorCookie('bucket', features);
+        writeGitBookVisitorCookie('bucket', { bucket: features });
     };
 
     // Determine if we're in a browser environment

packages/adaptive/src/utils.ts

@@ -18,5 +18,19 @@ export function writeGitBookVisitorCookie(name: string, value: unknown) {
 
     Cookies.set(COOKIE_NAME, COOKIE_VALUE, {
         secure: true,
+        domain: `.${getParentDomain()}`,
     });
 }
+
+function getParentDomain(): string {
+    const hostname = window.location.hostname;
+    const parts = hostname.split('.');
+    // If it's a subdomain (has at least 3 parts, like 'blog.example.com')
+    if (parts.length > 2) {
+        // Return the parent domain (last 2 parts)
+        return parts.slice(-2).join('.');
+    }
+
+    // Already a top-level domain
+    return hostname;
+}