diff --git a/tests/twitter-client.engagement.test.ts b/tests/twitter-client.engagement.test.ts
index dec4d33..f2d6ddb 100644
--- a/tests/twitter-client.engagement.test.ts
+++ b/tests/twitter-client.engagement.test.ts
@@ -1,6 +1,6 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 import { TwitterClient } from '../src/lib/twitter-client.js';
-import { validCookies } from './twitter-client-fixtures.js';
+import { testRelayBaseUrl } from './twitter-client-fixtures.js';
 
 const originalFetch = global.fetch;
 
@@ -25,7 +25,7 @@ describe('TwitterClient engagement', () => {
         json: async () => ({ data: { favorite_tweet: 'Done' } }),
       });
 
-      const client = new TwitterClient({ cookies: validCookies });
+      const client = new TwitterClient({ relayBaseUrl: testRelayBaseUrl });
       const result = await client.like('1234567890');
 
       expect(result.success).toBe(true);
@@ -45,7 +45,7 @@ describe('TwitterClient engagement', () => {
         text: async () => 'Forbidden',
       });
 
-      const client = new TwitterClient({ cookies: validCookies });
+      const client = new TwitterClient({ relayBaseUrl: testRelayBaseUrl });
       const result = await client.like('1234567890');
 
       expect(result.success).toBe(false);
@@ -61,7 +61,7 @@ describe('TwitterClient engagement', () => {
         }),
       });
 
-      const client = new TwitterClient({ cookies: validCookies });
+      const client = new TwitterClient({ relayBaseUrl: testRelayBaseUrl });
       const result = await client.like('1234567890');
 
       expect(result.success).toBe(false);
@@ -75,7 +75,7 @@ describe('TwitterClient engagement', () => {
         json: async () => ({ data: { favorite_tweet: 'Done' } }),
       });
 
-      const client = new TwitterClient({ cookies: validCookies });
+      const client = new TwitterClient({ relayBaseUrl: testRelayBaseUrl });
       const result = await client.like('1234567890');
 
       expect(result.success).toBe(true);
@@ -91,7 +91,7 @@ describe('TwitterClient engagement', () => {
         json: async () => ({ data: { unfavorite_tweet: 'Done' } }),
       });
 
-      const client = new TwitterClient({ cookies: validCookies });
+      const client = new TwitterClient({ relayBaseUrl: testRelayBaseUrl });
       const result = await client.unlike('1234567890');
 
       expect(result.success).toBe(true);
@@ -111,7 +111,7 @@ describe('TwitterClient engagement', () => {
         json: async () => ({ data: { create_retweet: { retweet_results: { result: {} } } } }),
       });
 
-      const client = new TwitterClient({ cookies: validCookies });
+      const client = new TwitterClient({ relayBaseUrl: testRelayBaseUrl });
       const result = await client.retweet('1234567890');
 
       expect(result.success).toBe(true);
@@ -131,7 +131,7 @@ describe('TwitterClient engagement', () => {
         json: async () => ({ data: { unretweet: { source_tweet_results: {} } } }),
       });
 
-      const client = new TwitterClient({ cookies: validCookies });
+      const client = new TwitterClient({ relayBaseUrl: testRelayBaseUrl });
       const result = await client.unretweet('1234567890');
 
       expect(result.success).toBe(true);
@@ -154,7 +154,7 @@ describe('TwitterClient engagement', () => {
         json: async () => ({ data: { tweet_bookmark_put: 'Done' } }),
       });
 
-      const client = new TwitterClient({ cookies: validCookies });
+      const client = new TwitterClient({ relayBaseUrl: testRelayBaseUrl });
       const result = await client.bookmark('1234567890');
 
       expect(result.success).toBe(true);
@@ -170,7 +170,7 @@ describe('TwitterClient engagement', () => {
     it('catches network errors', async () => {
       mockFetch.mockRejectedValueOnce(new Error('Network error'));
 
-      const client = new TwitterClient({ cookies: validCookies });
+      const client = new TwitterClient({ relayBaseUrl: testRelayBaseUrl });
       const result = await client.like('1234567890');
 
       expect(result.success).toBe(false);
diff --git a/tests/twitter-client.user-about.test.ts b/tests/twitter-client.user-about.test.ts
index 73d7e68..e168bd4 100644
--- a/tests/twitter-client.user-about.test.ts
+++ b/tests/twitter-client.user-about.test.ts
@@ -1,6 +1,6 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 import { TwitterClient } from '../src/lib/twitter-client.js';
-import { validCookies } from './twitter-client-fixtures.js';
+import { testRelayBaseUrl } from './twitter-client-fixtures.js';
 
 const originalFetch = global.fetch;
 
@@ -38,7 +38,7 @@ describe('TwitterClient getUserAboutAccount', () => {
       }),
     });
 
-    const client = new TwitterClient({ cookies: validCookies });
+    const client = new TwitterClient({ relayBaseUrl: testRelayBaseUrl });
     const result = await client.getUserAboutAccount('testuser');
 
     expect(result.success).toBe(true);
@@ -67,7 +67,7 @@ describe('TwitterClient getUserAboutAccount', () => {
       }),
     });
 
-    const client = new TwitterClient({ cookies: validCookies });
+    const client = new TwitterClient({ relayBaseUrl: testRelayBaseUrl });
     const result = await client.getUserAboutAccount('@testuser');
 
     expect(result.success).toBe(true);
@@ -75,7 +75,7 @@ describe('TwitterClient getUserAboutAccount', () => {
   });
 
   it('returns error for invalid username', async () => {
-    const client = new TwitterClient({ cookies: validCookies });
+    const client = new TwitterClient({ relayBaseUrl: testRelayBaseUrl });
     const result = await client.getUserAboutAccount('');
 
     expect(result.success).toBe(false);
@@ -95,7 +95,7 @@ describe('TwitterClient getUserAboutAccount', () => {
       }),
     });
 
-    const client = new TwitterClient({ cookies: validCookies });
+    const client = new TwitterClient({ relayBaseUrl: testRelayBaseUrl });
     const result = await client.getUserAboutAccount('testuser');
 
     expect(result.success).toBe(false);
@@ -111,7 +111,7 @@ describe('TwitterClient getUserAboutAccount', () => {
       }),
     });
 
-    const client = new TwitterClient({ cookies: validCookies });
+    const client = new TwitterClient({ relayBaseUrl: testRelayBaseUrl });
     const result = await client.getUserAboutAccount('testuser');
 
     expect(result.success).toBe(false);
@@ -125,7 +125,7 @@ describe('TwitterClient getUserAboutAccount', () => {
       text: async () => 'Not Found',
     });
 
-    const client = new TwitterClient({ cookies: validCookies });
+    const client = new TwitterClient({ relayBaseUrl: testRelayBaseUrl });
     const result = await client.getUserAboutAccount('testuser');
 
     expect(result.success).toBe(false);
@@ -139,7 +139,7 @@ describe('TwitterClient getUserAboutAccount', () => {
       text: async () => 'Internal Server Error',
     });
 
-    const client = new TwitterClient({ cookies: validCookies });
+    const client = new TwitterClient({ relayBaseUrl: testRelayBaseUrl });
     const result = await client.getUserAboutAccount('testuser');
 
     expect(result.success).toBe(false);
@@ -149,7 +149,7 @@ describe('TwitterClient getUserAboutAccount', () => {
   it('handles network errors', async () => {
     mockFetch.mockRejectedValueOnce(new Error('Network error'));
 
-    const client = new TwitterClient({ cookies: validCookies });
+    const client = new TwitterClient({ relayBaseUrl: testRelayBaseUrl });
     const result = await client.getUserAboutAccount('testuser');
 
     expect(result.success).toBe(false);
@@ -174,7 +174,7 @@ describe('TwitterClient getUserAboutAccount', () => {
       }),
     });
 
-    const client = new TwitterClient({ cookies: validCookies });
+    const client = new TwitterClient({ relayBaseUrl: testRelayBaseUrl });
     const result = await client.getUserAboutAccount('testuser');
 
     expect(result.success).toBe(true);
diff --git a/z-ai/lessons.md b/z-ai/lessons.md
index c98ae42..af9c08c 100644
--- a/z-ai/lessons.md
+++ b/z-ai/lessons.md
@@ -5,3 +5,4 @@
 - When the user asks to investigate odd API counts, do not change client-side limiting behavior unless they explicitly approve the behavior change.
 - When adding package registry publishing for this repository, use the `@yuta` package scope unless the user explicitly asks for another namespace.
 - Gitea Actions secret and variable names are case-insensitive, alphanumeric or underscore only, and cannot start with `GITEA_` or `GITHUB_`; use names like `PACKAGE_TOKEN`.
+- When adapting upstream tests to this fork, run tests with `TWITTER_RELAY_BASE_URL` unset; local relay environment variables can hide missing explicit `relayBaseUrl` fixtures.