diff --git a/tests/test_client.py b/tests/test_client.py
index c1393d3..dd4c15a 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -1545,3 +1545,54 @@ def mock_post(operation_name, variables, features=None):
 
         assert captured.get("product") == "Latest"
         assert captured.get("querySource") == "typed_query"
+
+
+# ── TwitterClient._ensure_client_transaction ─────────────────────────────
+
+class TestEnsureClientTransaction:
+    """The x.com fetch must be authenticated.
+
+    Anonymous requests receive the logged-out landing page, which carries no
+    ondemand.s marker, so get_ondemand_file_url() fails and every subsequent
+    API call goes out without an x-client-transaction-id header.
+    """
+
+    def _make_client(self):
+        client = TwitterClient.__new__(TwitterClient)
+        client._auth_token = "test_token"
+        client._ct0 = "test_ct0"
+        client._cookie_string = None
+        client._client_transaction = None
+        client._ct_init_attempted = False
+        return client
+
+    @patch("twitter_cli.client._gen_ct_headers", return_value={})
+    @patch("twitter_cli.client._get_cffi_session")
+    def test_homepage_fetch_sends_cookies(self, mock_session, mock_ct_headers):
+        session = MagicMock()
+        session.get = MagicMock(side_effect=Exception("stop after first fetch"))
+        mock_session.return_value = session
+
+        client = self._make_client()
+        client._load_ct_cache = lambda: False
+        client._ensure_client_transaction()
+
+        _, kwargs = session.get.call_args
+        cookie = kwargs["headers"]["Cookie"]
+        assert "auth_token=test_token" in cookie
+        assert "ct0=test_ct0" in cookie
+
+    @patch("twitter_cli.client._gen_ct_headers", return_value={})
+    @patch("twitter_cli.client._get_cffi_session")
+    def test_full_cookie_string_preferred(self, mock_session, mock_ct_headers):
+        session = MagicMock()
+        session.get = MagicMock(side_effect=Exception("stop after first fetch"))
+        mock_session.return_value = session
+
+        client = self._make_client()
+        client._cookie_string = "auth_token=a; ct0=b; guest_id=c"
+        client._load_ct_cache = lambda: False
+        client._ensure_client_transaction()
+
+        _, kwargs = session.get.call_args
+        assert kwargs["headers"]["Cookie"] == "auth_token=a; ct0=b; guest_id=c"
diff --git a/twitter_cli/client.py b/twitter_cli/client.py
index 0436c8e..8232190 100644
--- a/twitter_cli/client.py
+++ b/twitter_cli/client.py
@@ -1103,6 +1103,13 @@ def _ensure_client_transaction(self):
             # a different TLS fingerprint on the same IP — a detection vector.
             cffi_session = _get_cffi_session()
             ct_headers = _gen_ct_headers()
+            # x.com serves the logged-out landing page to anonymous requests,
+            # and that page contains no ondemand.s marker for
+            # get_ondemand_file_url() to match. Send the session cookies so we
+            # receive the authenticated app shell instead.
+            ct_headers["Cookie"] = self._cookie_string or (
+                "auth_token=%s; ct0=%s" % (self._auth_token, self._ct0)
+            )
             home_page = cffi_session.get(
                 "https://x.com", headers=ct_headers, timeout=10,
             )