fix: mirror django request user agent into $raw_user_agent

[lricoy]

💡 Motivation and Context

The Django middleware tags all events in a request with $user_agent, but PostHog's server-side classification — web analytics bot detection ($virt_is_bot and friends) and the materialized-column fast path — keys on the standardized $raw_user_agent property (the one posthog-js sends). Server-side-tracked pageviews forwarding a real client UA are exactly the traffic where bot classification matters, and today they miss it.

PostHog/posthog#68253 removes the $user_agent query-time fallback for performance (it forced a full properties-blob read on every classification query — see the PR for production measurements), so this change mirrors the header into $raw_user_agent, aligning the middleware with the standardized property. Related: PostHog/posthog#68232.

$user_agent is still sent for backwards compatibility.

💚 How did you test it?

Agent-authored. Extended test_extract_tags_basic to assert both properties carry the request's User-Agent header; ran the middleware extract_tags tests locally (11 passed).

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• Changeset added in .sampo/changesets/.

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Built with Claude Code as part of a cross-repo effort to standardize on $raw_user_agent (PostHog/posthog#68232, PostHog/posthog#68253, with sibling PRs to posthog-android and posthog-ruby).

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix: mirror django request user agent in..." | Re-trigger Greptile}

[github-actions]

posthog-python Compliance Report

Date: 2026-07-03 15:28:00 UTC
Duration: 177187ms

✅ All Tests Passed!

46/46 tests passed

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Capture Tests

✅ 29/29 tests passed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	516ms
Format Validation.Event Has Uuid	✅	1507ms
Format Validation.Event Has Lib Properties	✅	1507ms
Format Validation.Distinct Id Is String	✅	1506ms
Format Validation.Token Is Present	✅	1508ms
Format Validation.Custom Properties Preserved	✅	1506ms
Format Validation.Event Has Timestamp	✅	1507ms
Retry Behavior.Retries On 503	✅	9516ms
Retry Behavior.Does Not Retry On 400	✅	3508ms
Retry Behavior.Does Not Retry On 401	✅	3507ms
Retry Behavior.Respects Retry After Header	✅	9510ms
Retry Behavior.Implements Backoff	✅	23532ms
Retry Behavior.Retries On 500	✅	7505ms
Retry Behavior.Retries On 502	✅	7507ms
Retry Behavior.Retries On 504	✅	7515ms
Retry Behavior.Max Retries Respected	✅	23529ms
Deduplication.Generates Unique Uuids	✅	1496ms
Deduplication.Preserves Uuid On Retry	✅	7515ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	14512ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	7516ms
Deduplication.No Duplicate Events In Batch	✅	1503ms
Deduplication.Different Events Have Different Uuids	✅	1507ms
Compression.Sends Gzip When Enabled	✅	1506ms
Batch Format.Uses Proper Batch Structure	✅	1507ms
Batch Format.Flush With No Events Sends Nothing	✅	1006ms
Batch Format.Multiple Events Batched Together	✅	1504ms
Error Handling.Does Not Retry On 403	✅	3508ms
Error Handling.Does Not Retry On 413	✅	3508ms
Error Handling.Retries On 408	✅	7514ms

Feature_Flags Tests

✅ 17/17 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	1004ms
Request Payload.Flags Request Uses V2 Query Param	✅	1006ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	1006ms
Request Payload.Flags Request Omits Authorization Header	✅	1007ms
Request Payload.Token In Flags Body Matches Init	✅	1006ms
Request Payload.Groups Round Trip	✅	1006ms
Request Payload.Groups Default To Empty Object	✅	1006ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	1006ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	1007ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	1006ms
Request Lifecycle.No Flags Request On Init Alone	✅	503ms
Request Lifecycle.No Flags Request On Normal Capture	✅	1506ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	1011ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	1002ms
Retry Behavior.Retries Flags On 502	✅	1006ms
Retry Behavior.Retries Flags On 504	✅	1006ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	1509ms