fix: fall back when payload compression fails

[marandaneto]

💡 Motivation and Context

When gzip=True, local gzip failures should not prevent the SDK from sending the batch. The SDK should fall back to the original uncompressed JSON payload without a Content-Encoding header.

This catches local gzip errors during request construction and keeps the upload path uncompressed. A unit test covers the fallback.

💚 How did you test it?

• uv run --extra test 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)

Implemented as part of a cross-SDK consistency pass for client-side compression failure fallback. Kept the change scoped to request construction and added a focused regression test.

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix: fall back when payload compression ..." | Re-trigger Greptile}

[github-actions]

posthog-python Compliance Report

Date: 2026-06-28 09:19:50 UTC
Duration: 530104ms

✅ All Tests Passed!

45/45 tests passed

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Capture Tests

✅ 29/29 tests passed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	518ms
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	✅	10008ms
Retry Behavior.Retries On 503	✅	18019ms
Retry Behavior.Does Not Retry On 400	✅	12004ms
Retry Behavior.Does Not Retry On 401	✅	10005ms
Retry Behavior.Respects Retry After Header	✅	16015ms
Retry Behavior.Implements Backoff	✅	30018ms
Retry Behavior.Retries On 500	✅	13012ms
Retry Behavior.Retries On 502	✅	16010ms
Retry Behavior.Retries On 504	✅	16011ms
Retry Behavior.Max Retries Respected	✅	30009ms
Deduplication.Generates Unique Uuids	✅	7011ms
Deduplication.Preserves Uuid On Retry	✅	16017ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	23019ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	16006ms
Deduplication.No Duplicate Events In Batch	✅	10002ms
Deduplication.Different Events Have Different Uuids	✅	10007ms
Compression.Sends Gzip When Enabled	✅	10008ms
Batch Format.Uses Proper Batch Structure	✅	10007ms
Batch Format.Flush With No Events Sends Nothing	✅	5005ms
Batch Format.Multiple Events Batched Together	✅	10006ms
Error Handling.Does Not Retry On 403	✅	12009ms
Error Handling.Does Not Retry On 413	✅	10007ms
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	✅	9502ms
Request Payload.Flags Request Uses V2 Query Param	✅	10007ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	10006ms
Request Payload.Flags Request Omits Authorization Header	✅	10007ms
Request Payload.Token In Flags Body Matches Init	✅	10007ms
Request Payload.Groups Round Trip	✅	10008ms
Request Payload.Groups Default To Empty Object	✅	10007ms
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	✅	9511ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	10003ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	10509ms