fix: send batch sent_at in snake case

[marandaneto]

💡 Motivation and Context

Python SDK batch requests currently send the top-level client submission timestamp as sentAt, but the batch ingestion backend reads sent_at. As a result, the backend ignores the value and skips clock-skew correction that depends on the batch-level sent timestamp.

This includes a patch changeset for pypi/posthog.

💚 How did you test it?

• uv run pytest posthog/test/test_request.py -q

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran sampo add to generate a changeset file

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

This PR was authored with Pi. The backend batch endpoint was cross-checked and found to deserialize sent_at, so the SDK was updated to emit the backend-supported snake_case field. A parameterized regression test ensures sent_at is present and the old sentAt key is absent. The changeset targets pypi/posthog.

[greptile-apps]

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

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### Issue 1 of 1
posthog/test/test_request.py:114-130
**Test not parameterised**

The team rule prefers parameterised tests. The two assertions here — `"sent_at"` must be present and `"sentAt"` must be absent — are independent enough to express as a `@pytest.mark.parametrize` table, which also makes it easy to extend the key allow/deny list without duplicating the mock setup.

_{Reviews (1): Last reviewed commit: "fix: send batch sent_at in snake case" | Re-trigger Greptile}

[github-actions]

posthog-python Compliance Report

Date: 2026-06-18 12:31:04 UTC
Duration: 540099ms

✅ All Tests Passed!

45/45 tests passed

---

Capture Tests

✅ 29/29 tests passed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	517ms
Format Validation.Event Has Uuid	✅	10007ms
Format Validation.Event Has Lib Properties	✅	10007ms
Format Validation.Distinct Id Is String	✅	10007ms
Format Validation.Token Is Present	✅	10007ms
Format Validation.Custom Properties Preserved	✅	10007ms
Format Validation.Event Has Timestamp	✅	10006ms
Retry Behavior.Retries On 503	✅	18020ms
Retry Behavior.Does Not Retry On 400	✅	12003ms
Retry Behavior.Does Not Retry On 401	✅	10008ms
Retry Behavior.Respects Retry After Header	✅	16014ms
Retry Behavior.Implements Backoff	✅	32028ms
Retry Behavior.Retries On 500	✅	16001ms
Retry Behavior.Retries On 502	✅	16010ms
Retry Behavior.Retries On 504	✅	16011ms
Retry Behavior.Max Retries Respected	✅	32027ms
Deduplication.Generates Unique Uuids	✅	9992ms
Deduplication.Preserves Uuid On Retry	✅	16016ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	23019ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	16005ms
Deduplication.No Duplicate Events In Batch	✅	10002ms
Deduplication.Different Events Have Different Uuids	✅	10007ms
Compression.Sends Gzip When Enabled	✅	10007ms
Batch Format.Uses Proper Batch Structure	✅	10007ms
Batch Format.Flush With No Events Sends Nothing	✅	5005ms
Batch Format.Multiple Events Batched Together	✅	10005ms
Error Handling.Does Not Retry On 403	✅	12009ms
Error Handling.Does Not Retry On 413	✅	10008ms
Error Handling.Retries On 408	✅	14013ms

Feature_Flags Tests

✅ 16/16 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	9501ms
Request Payload.Flags Request Uses V2 Query Param	✅	10007ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	10007ms
Request Payload.Flags Request Omits Authorization Header	✅	10007ms
Request Payload.Token In Flags Body Matches Init	✅	10007ms
Request Payload.Groups Round Trip	✅	10007ms
Request Payload.Groups Default To Empty Object	✅	10006ms
Request Payload.Person Properties Distinct Id Auto Populated When Caller Omits It	✅	10007ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	10007ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	10007ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	10007ms
Request Lifecycle.No Flags Request On Init Alone	✅	5003ms
Request Lifecycle.No Flags Request On Normal Capture	✅	10508ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	9510ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	10003ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	10509ms

[greptile-apps]

_{Reviews (2): Last reviewed commit: "address pr review feedback" | Re-trigger Greptile}

[ioannisj]

CI is not happy here?

[marandaneto]

CI is not happy here?

blocked by #677 which is now merged and ok