Cover webhooks to internal hosts when they are allowed

Every webhook test that reaches a real socket ran with internal requests
disallowed, and the rest intercept above the transport. Wiring the
transport to always disallow internal addresses would therefore have
passed the suite while breaking webhooks to internal hosts on every
default install.

A new test sends a webhook to localhost with internal requests allowed
and checks that the payload arrives and that the guard resolved nothing.
The Host header test's docstring is also corrected: the header now comes
from the URL, not from a resolved hostname.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/documents/tests/test_workflows.py

@@ -5192,6 +5192,35 @@ class TestWebhookSecurity:
         assert received.body == b"hi"
         assert received.headers["host"] == f"webhook.test:{local_http_server.port}"
 
+    @override_settings(WEBHOOKS_ALLOW_INTERNAL_REQUESTS=True)
+    def test_allow_internal_sends_to_internal_address(
+        self,
+        local_http_server: LocalHTTPServer,
+        fake_dns: FakeDNS,
+    ) -> None:
+        """
+        GIVEN:
+            - A webhook to localhost
+            - WEBHOOKS_ALLOW_INTERNAL_REQUESTS is True
+        WHEN:
+            - send_webhook is called
+        THEN:
+            - The payload arrives at the internal address
+            - The guard does not resolve the host, leaving it to the stock
+              connection path
+        """
+        send_webhook(
+            url=f"http://localhost:{local_http_server.port}",
+            data="hi",
+            headers={},
+            files=None,
+            as_json=False,
+        )
+
+        received = local_http_server.requests[0]
+        assert received.body == b"hi"
+        assert fake_dns.lookups == []
+
     @override_settings(WEBHOOKS_ALLOW_INTERNAL_REQUESTS=False)
     def test_block_is_an_expected_task_failure(
         self,
@@ -5267,7 +5296,7 @@ class TestWebhookSecurity:
         WHEN:
             - send_webhook is called with a malicious Host header
         THEN:
-            - The Host header is stripped and replaced with the resolved hostname
+            - The Host header is stripped and set from the URL hostname
         """
         httpx_mock.add_response(content=b"ok")