fix: mirror django request user agent into $raw_user_agent

.sampo/changesets/mirror-raw-user-agent.md

@@ -0,0 +1,5 @@
+---
+"posthog": patch
+---
+
+Django middleware also sends the request user agent as `$raw_user_agent`, the standardized property PostHog's server-side classification (e.g. bot detection) reads

posthog/integrations/django.py

@@ -202,10 +202,12 @@ def _build_tags(self, request, user_id, user_email):
         if ip_address:
             tags["$ip"] = ip_address
 
-        # Extract user agent
+        # Extract user agent, mirrored into $raw_user_agent — the standardized
+        # property PostHog's server-side classification (e.g. bot detection) reads
         user_agent = request.headers.get("User-Agent")
         if user_agent:
             tags["$user_agent"] = user_agent
+            tags["$raw_user_agent"] = user_agent
 
         # Apply extra tags if configured
         if self.extra_tags:

posthog/test/integrations/test_middleware.py

@@ -90,6 +90,7 @@ def test_extract_tags_basic(self):
                 headers={
                     "X-POSTHOG-SESSION-ID": "session-123",
                     "X-POSTHOG-DISTINCT-ID": "user-456",
+                    "User-Agent": "TestAgent/1.0",
                 },
                 method="POST",
                 path="/api/test",
@@ -103,6 +104,8 @@ def test_extract_tags_basic(self):
             self.assertEqual(get_context_distinct_id(), "user-456")
             self.assertEqual(tags["$current_url"], "https://example.com/api/test")
             self.assertEqual(tags["$request_method"], "POST")
+            self.assertEqual(tags["$user_agent"], "TestAgent/1.0")
+            self.assertEqual(tags["$raw_user_agent"], "TestAgent/1.0")
 
     def test_extract_tags_missing_headers(self):
         """Test tag extraction when PostHog headers are missing"""