diff --git a/tests/test_client.py b/tests/test_client.py
index c1393d3..a116588 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -332,6 +332,63 @@ def test_cookie_string_used_when_available(
         assert headers["sec-ch-ua-platform-version"] == '""'
 
 
+# ── TwitterClient._ensure_client_transaction ─────────────────────────────
+
+class TestEnsureClientTransaction:
+    """The x.com bootstrap fetch must be authenticated.
+
+    Logged out, x.com serves the new "x-web" shell whose HTML has no
+    `ondemand.s` chunk map, so no transaction ID can ever be generated and
+    every transaction-gated endpoint (SearchTimeline included) 404s.
+    """
+
+    @staticmethod
+    def _client(cookie_string=None):
+        client = TwitterClient.__new__(TwitterClient)
+        client._auth_token = "token"
+        client._ct0 = "ct0"
+        client._cookie_string = cookie_string
+        client._client_transaction = None
+        client._ct_init_attempted = False
+        return client
+
+    @patch("twitter_cli.client._get_cffi_session")
+    @patch("twitter_cli.client._gen_ct_headers", return_value={})
+    def _bootstrap_headers(self, cookie_string, mock_ct_headers, mock_session):
+        session = MagicMock()
+        # Abort right after the homepage fetch — we only assert on its headers.
+        session.get = MagicMock(side_effect=Exception("stop after homepage"))
+        mock_session.return_value = session
+
+        client = self._client(cookie_string)
+        with patch.object(client, "_load_ct_cache", return_value=False):
+            client._ensure_client_transaction()
+
+        assert session.get.call_args[0][0] == "https://x.com"
+        return session.get.call_args[1]["headers"]
+
+    def test_homepage_fetch_sends_session_cookies(self):
+        headers = self._bootstrap_headers(None)
+        assert headers["Cookie"] == "auth_token=token; ct0=ct0"
+
+    def test_homepage_fetch_prefers_full_cookie_string(self):
+        headers = self._bootstrap_headers("auth_token=x; ct0=y; other=z")
+        assert headers["Cookie"] == "auth_token=x; ct0=y; other=z"
+
+    @patch("twitter_cli.client._get_cffi_session")
+    @patch("twitter_cli.client._gen_ct_headers", return_value={})
+    def test_bootstrap_failure_is_not_fatal(self, mock_ct_headers, mock_session):
+        session = MagicMock()
+        session.get = MagicMock(side_effect=Exception("network down"))
+        mock_session.return_value = session
+
+        client = self._client()
+        with patch.object(client, "_load_ct_cache", return_value=False):
+            client._ensure_client_transaction()
+
+        assert client._client_transaction is None
+
+
 class TestPaginationBehavior:
     def test_fetch_timeline_can_include_promoted_content(self):
         client = TwitterClient.__new__(TwitterClient)
diff --git a/twitter_cli/client.py b/twitter_cli/client.py
index 0436c8e..39d2031 100644
--- a/twitter_cli/client.py
+++ b/twitter_cli/client.py
@@ -1103,8 +1103,17 @@ 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()
+            # Send session cookies: the logged-OUT x.com shell is now the new
+            # "x-web" build, whose HTML carries no `ondemand.s` chunk map, so
+            # get_ondemand_file_url() finds nothing and transaction IDs never
+            # get generated. The logged-in shell still serves the
+            # responsive-web client-web bundle that does carry the map.
+            home_headers = dict(ct_headers)
+            home_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,
+                "https://x.com", headers=home_headers, timeout=10,
             )
             home_page_response = bs4.BeautifulSoup(home_page.content, "html.parser")
             ondemand_url = get_ondemand_file_url(response=home_page_response)