From d303de574270656bbb4cd037b88faac6e1e6171c Mon Sep 17 00:00:00 2001
From: Ravi Kumar L <ravi.lazar@clickhouse.com>
Date: Fri, 10 Jul 2026 21:34:20 +0200
Subject: [PATCH] fix(langfuse): align startup fanout gate

---
 api/server/routes/__tests__/config.spec.js | 19 +++++++++++++++++++
 api/server/routes/config.js                |  5 ++---
 packages/api/src/langfuse/index.ts         |  1 +
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/api/server/routes/__tests__/config.spec.js b/api/server/routes/__tests__/config.spec.js
index af82399e76..592f72ab06 100644
--- a/api/server/routes/__tests__/config.spec.js
+++ b/api/server/routes/__tests__/config.spec.js
@@ -104,6 +104,8 @@ afterEach(() => {
   delete process.env.ANALYTICS_GTM_ID;
   delete process.env.CUSTOM_FOOTER;
   delete process.env.HELP_AND_FAQ_URL;
+  delete process.env.LANGFUSE_FANOUT_ENABLED;
+  delete process.env.LANGFUSE_FANOUT_COLLECTOR_URL;
 });
 
 describe('GET /api/config', () => {
@@ -383,6 +385,23 @@ describe('GET /api/config', () => {
       expect(response.body.conversationImportMaxFileSize).toBe(5000000);
     });
 
+    it('should advertise Langfuse fanout only when the toggle and collector URL are configured', async () => {
+      mockGetAppConfig.mockResolvedValue(baseAppConfig);
+      process.env.LANGFUSE_FANOUT_ENABLED = 'true';
+      const app = createApp(mockUser);
+
+      let response = await request(app).get('/api/config');
+      expect(response.body.langfuseFanoutEnabled).toBe(false);
+
+      process.env.LANGFUSE_FANOUT_COLLECTOR_URL = '   ';
+      response = await request(app).get('/api/config');
+      expect(response.body.langfuseFanoutEnabled).toBe(false);
+
+      process.env.LANGFUSE_FANOUT_COLLECTOR_URL = 'http://langfuse-fanout:4318';
+      response = await request(app).get('/api/config');
+      expect(response.body.langfuseFanoutEnabled).toBe(true);
+    });
+
     it('should include post-login informational fields', async () => {
       process.env.ANALYTICS_GTM_ID = 'GTM-XYZ';
       process.env.CUSTOM_FOOTER = 'authenticated footer text';
diff --git a/api/server/routes/config.js b/api/server/routes/config.js
index 47c84f6fcd..cb6237f0c4 100644
--- a/api/server/routes/config.js
+++ b/api/server/routes/config.js
@@ -1,6 +1,7 @@
 const express = require('express');
 const {
   isEnabled,
+  isLangfuseFanoutEnabled,
   getBalanceConfig,
   getCloudFrontConfig,
   resolveBuildInfo,
@@ -277,9 +278,7 @@ router.get('/', async function (req, res) {
       conversationImportMaxFileSize: process.env.CONVERSATION_IMPORT_MAX_FILE_SIZE_BYTES
         ? parseInt(process.env.CONVERSATION_IMPORT_MAX_FILE_SIZE_BYTES, 10)
         : 0,
-      langfuseFanoutEnabled: /^(true|1|yes|on)$/i.test(
-        (process.env.LANGFUSE_FANOUT_ENABLED ?? '').trim(),
-      ),
+      langfuseFanoutEnabled: isLangfuseFanoutEnabled(),
       ...(cloudFront ? { cloudFront } : {}),
       ...(rum ? { rum } : {}),
     };
diff --git a/packages/api/src/langfuse/index.ts b/packages/api/src/langfuse/index.ts
index b22dba4698..43a5de0f83 100644
--- a/packages/api/src/langfuse/index.ts
+++ b/packages/api/src/langfuse/index.ts
@@ -1,2 +1,3 @@
 export * from './feedback';
 export * from './trace';
+export { isLangfuseFanoutEnabled } from './config';