diff --git a/apps/sim/proxy.test.ts b/apps/sim/proxy.test.ts
index 0282d670cd..9311b14635 100644
--- a/apps/sim/proxy.test.ts
+++ b/apps/sim/proxy.test.ts
@@ -44,7 +44,7 @@ describe('resolveApiCorsPolicy', () => {
     expect(policy.headers).toContain('X-API-Key')
   })
 
-  it('reflects origin for chat and form embeds, never sets credentials', () => {
+  it('reflects origin for chat and form embeds with credentials enabled', () => {
     const paths = [
       '/api/chat/abc',
       '/api/chat/abc/otp',
@@ -56,13 +56,19 @@ describe('resolveApiCorsPolicy', () => {
       const policy = resolveApiCorsPolicy(makeRequest(path, 'https://customer.example'))
       expect(policy).toEqual({
         origin: 'https://customer.example',
-        credentials: false,
+        credentials: true,
         methods: 'GET, POST, PUT, OPTIONS',
         headers: 'Content-Type, X-Requested-With',
       })
     }
   })
 
+  it('drops credentials on embed policy when Origin header is absent (CORS spec invariant)', () => {
+    const policy = resolveApiCorsPolicy(makeRequest('/api/chat/abc'))
+    expect(policy.origin).toBe('*')
+    expect(policy.credentials).toBe(false)
+  })
+
   it('allows PUT on the embed policy (used by OTP verification on /[identifier]/otp)', () => {
     const policy = resolveApiCorsPolicy(
       makeRequest('/api/chat/abc/otp', 'https://customer.example')
@@ -70,16 +76,12 @@ describe('resolveApiCorsPolicy', () => {
     expect(policy.methods).toContain('PUT')
   })
 
-  it('falls back to wildcard for chat/form embeds when no origin header is present', () => {
-    expect(resolveApiCorsPolicy(makeRequest('/api/chat/abc')).origin).toBe('*')
-  })
-
   it('applies the embed policy to future identifier subroutes (not just /otp, /sso)', () => {
     const policy = resolveApiCorsPolicy(
       makeRequest('/api/chat/abc/transcript', 'https://customer.example')
     )
     expect(policy.origin).toBe('https://customer.example')
-    expect(policy.credentials).toBe(false)
+    expect(policy.credentials).toBe(true)
   })
 
   it('uses the default credentialed policy for workspace-internal chat/form routes', () => {
diff --git a/apps/sim/proxy.ts b/apps/sim/proxy.ts
index a5b8ea6df9..1bf1ccac50 100644
--- a/apps/sim/proxy.ts
+++ b/apps/sim/proxy.ts
@@ -22,19 +22,10 @@ const DEFAULT_API_ALLOWED_HEADERS =
 const WORKFLOW_EXECUTE_HEADERS =
   'X-CSRF-Token, X-Requested-With, Accept, Accept-Version, Content-Length, Content-MD5, Content-Type, Date, X-Api-Version, X-API-Key'
 
-/**
- * Workspace-internal segments under /api/{chat,form}/* that must NOT
- * receive the embed policy. They serve the workspace UI with session
- * cookies and need the default credentialed policy.
- */
+/** Subpaths under /api/{chat,form}/* that serve the workspace UI, not embeds. */
 const EMBED_RESERVED_SEGMENTS = new Set(['manage', 'validate'])
 
-/**
- * True for /api/{chat,form}/[identifier] and any deeper subroute
- * (e.g. /otp, /sso). The identifier segment is explicitly checked
- * against EMBED_RESERVED_SEGMENTS so workspace-internal routes fall
- * through to the default credentialed policy.
- */
+/** True for /api/{chat,form}/[identifier] and any deeper subroute. */
 function isEmbedPath(pathname: string): boolean {
   const segments = pathname.split('/')
   if (segments.length < 4) return false
@@ -79,20 +70,16 @@ const CORS_RULES: readonly CorsRule[] = [
     }),
   },
   {
-    // Embed endpoints: /api/chat/[identifier] and /api/form/[identifier]
-    // (plus their /otp and /sso subroutes). These run on customer domains —
-    // reflect the request origin and omit credentials (auth uses signed
-    // tokens, not cookies). Workspace-internal subpaths (`manage`, `validate`,
-    // and the bare collection routes) are deliberately excluded so they
-    // continue to receive the default credentialed policy.
     match: (p) => isEmbedPath(p),
-    policy: (request) => ({
-      origin: request.headers.get('origin') || '*',
-      credentials: false,
-      // PUT is required for OTP verification on /[identifier]/otp.
-      methods: 'GET, POST, PUT, OPTIONS',
-      headers: 'Content-Type, X-Requested-With',
-    }),
+    policy: (request) => {
+      const requestOrigin = request.headers.get('origin')
+      return {
+        origin: requestOrigin || '*',
+        credentials: !!requestOrigin,
+        methods: 'GET, POST, PUT, OPTIONS',
+        headers: 'Content-Type, X-Requested-With',
+      }
+    },
   },
   {
     match: (p) => /^\/api\/workflows\/[^/]+\/execute$/.test(p),
@@ -105,10 +92,7 @@ const CORS_RULES: readonly CorsRule[] = [
   },
 ]
 
-/**
- * Single source of truth for CORS on /api/* — next.config.ts headers are
- * baked at build time and would freeze NEXT_PUBLIC_APP_URL into the image.
- */
+/** Single source of truth for /api/* CORS — resolved at request time, not baked at build. */
 export function resolveApiCorsPolicy(request: NextRequest): CorsPolicy {
   const { pathname } = request.nextUrl
   for (const rule of CORS_RULES) {
@@ -134,10 +118,7 @@ function applyCorsHeaders(response: NextResponse, policy: CorsPolicy): void {
   }
 }
 
-/**
- * Short-circuit preflight: Next's auto-OPTIONS for route handlers without
- * an explicit OPTIONS export does not carry middleware headers.
- */
+/** Next's auto-OPTIONS doesn't carry middleware headers, so we answer preflight here. */
 function buildPreflightResponse(policy: CorsPolicy): NextResponse {
   const response = new NextResponse(null, { status: 204 })
   applyCorsHeaders(response, policy)