diff --git a/packages/owletto-backend/src/auth/index.ts b/packages/owletto-backend/src/auth/index.ts
index 97fd0b019..ca7c62454 100644
--- a/packages/owletto-backend/src/auth/index.ts
+++ b/packages/owletto-backend/src/auth/index.ts
@@ -126,6 +126,17 @@ export async function createAuth(env: Env, request?: Request) {
   // Also trust the baseURL (resolves from PUBLIC_WEB_URL, forwarded headers, or request URL)
   addTrustedOriginVariants(resolveBaseUrl({ request }));
 
+  // When AUTH_COOKIE_DOMAIN is set (e.g. ".lobu.ai"), trust all subdomains so
+  // session cookies travel across {org}.lobu.ai → lobu.ai cross-origin requests.
+  const cookieDomain = process.env.AUTH_COOKIE_DOMAIN?.trim();
+  if (cookieDomain) {
+    const normalized = cookieDomain.startsWith('.') ? cookieDomain.slice(1) : cookieDomain;
+    if (normalized) {
+      trustedOriginSet.add(`https://*.${normalized}`);
+      trustedOriginSet.add(`https://${normalized}`);
+    }
+  }
+
   const auth = betterAuth({
     secret: env.BETTER_AUTH_SECRET,
     database: pool,
diff --git a/packages/owletto-backend/src/index.ts b/packages/owletto-backend/src/index.ts
index d182e5fda..a55a15949 100644
--- a/packages/owletto-backend/src/index.ts
+++ b/packages/owletto-backend/src/index.ts
@@ -264,8 +264,23 @@ app.use('/*', async (c, next) => {
 
 /**
  * Subdomain org extraction middleware
- * Parses Host header for {org}.{baseDomain} pattern and sets subdomainOrg
+ * Parses Host header for {org}.{baseDomain} pattern and sets subdomainOrg.
+ * Reserved subdomains (www, api, app, admin, etc.) are not treated as orgs.
  */
+const RESERVED_SUBDOMAINS = new Set([
+  'www',
+  'api',
+  'app',
+  'admin',
+  'auth',
+  'mcp',
+  'static',
+  'assets',
+  'cdn',
+  'docs',
+  'mail',
+]);
+
 app.use('/*', async (c, next) => {
   c.set('subdomainOrg', null);
   const baseUrlValue = getConfiguredPublicOrigin();
@@ -275,7 +290,7 @@ app.use('/*', async (c, next) => {
       const host = c.req.header('host')?.split(':')[0];
       if (host?.endsWith(`.${baseDomain}`)) {
         const sub = host.slice(0, -(baseDomain.length + 1));
-        if (sub && !sub.includes('.')) {
+        if (sub && !sub.includes('.') && !RESERVED_SUBDOMAINS.has(sub.toLowerCase())) {
           c.set('subdomainOrg', sub);
         }
       }
diff --git a/packages/owletto-backend/src/utils/__tests__/public-origin.test.ts b/packages/owletto-backend/src/utils/__tests__/public-origin.test.ts
index ea15f8252..e3212c0fb 100644
--- a/packages/owletto-backend/src/utils/__tests__/public-origin.test.ts
+++ b/packages/owletto-backend/src/utils/__tests__/public-origin.test.ts
@@ -31,4 +31,19 @@ describe('getCanonicalRedirectUrl', () => {
       getCanonicalRedirectUrl('http://localhost:8787/brand/acme', 'https://community.lobu.ai')
     ).toBeNull();
   });
+
+  it('preserves sibling subdomains under the auth cookie zone', () => {
+    expect(
+      getCanonicalRedirectUrl('https://acme.lobu.ai/dashboard', 'https://app.lobu.ai', '.lobu.ai')
+    ).toBeNull();
+    expect(
+      getCanonicalRedirectUrl('https://lobu.ai/marketing', 'https://app.lobu.ai', '.lobu.ai')
+    ).toBeNull();
+  });
+
+  it('still redirects unrelated hosts when a cookie zone is set', () => {
+    expect(
+      getCanonicalRedirectUrl('https://owletto.com/foo', 'https://app.lobu.ai', '.lobu.ai')
+    ).toBe('https://app.lobu.ai/foo');
+  });
 });
diff --git a/packages/owletto-backend/src/utils/public-origin.ts b/packages/owletto-backend/src/utils/public-origin.ts
index 80bf88967..22cbdc573 100644
--- a/packages/owletto-backend/src/utils/public-origin.ts
+++ b/packages/owletto-backend/src/utils/public-origin.ts
@@ -75,11 +75,14 @@ const LOCALHOST_HOSTNAMES = new Set(['localhost', '127.0.0.1', '::1', '[::1]']);
 /**
  * Returns a canonical redirect URL when browser traffic lands on a non-canonical
  * host while a public origin is configured. Subdomains of the canonical host are
- * preserved so workspace routing keeps working.
+ * preserved so workspace routing keeps working. When AUTH_COOKIE_DOMAIN is set
+ * (e.g. ".lobu.ai") sibling subdomains of that zone are also preserved so
+ * per-org subdomains like acme.lobu.ai are not bounced to app.lobu.ai.
  */
 export function getCanonicalRedirectUrl(
   requestUrl: string,
-  configuredOrigin = getConfiguredPublicOrigin()
+  configuredOrigin = getConfiguredPublicOrigin(),
+  cookieDomain = process.env.AUTH_COOKIE_DOMAIN
 ): string | null {
   if (!configuredOrigin) return null;
 
@@ -102,5 +105,10 @@ export function getCanonicalRedirectUrl(
     return null;
   }
 
+  const cookieZone = cookieDomain?.trim().replace(/^\./, '').toLowerCase();
+  if (cookieZone && (requestHost === cookieZone || requestHost.endsWith(`.${cookieZone}`))) {
+    return null;
+  }
+
   return `${canonical.origin}${request.pathname}${request.search}`;
 }