feat: SDK Compliance

[jose-sequeira]

Integrate the SDK Test Harness to validate SDK compliance against the shared capture API contract.

This adds:

• An SDK adapter that wraps this SDK and exposes the standard REST interface for the test harness
• A CI workflow that runs compliance tests on every PR and push to the default branch
• A Dockerfile for running the adapter in the test harness environment

The test harness runs a mock PostHog server, exercises the SDK through the adapter, and verifies behavior matches the contract defined in CONTRACT.yaml (event format, retries, compression, deduplication, etc.).

[github-actions]

PostHog SDK Compliance Report

SDK: posthog-python
Date: 2026-01-20 12:15:16 UTC
Duration: 72974ms

⚠️ Some Tests Failed

14/17 tests passed, 3 failed

---

Capture Tests

⚠️ 14/17 tests passed, 3 failed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	516ms
Format Validation.Event Has Uuid	✅	1507ms
Format Validation.Event Has Lib Properties	✅	1506ms
Format Validation.Distinct Id Is String	✅	1507ms
Format Validation.Token Is Present	✅	1506ms
Retry Behavior.Retries On 503	✅	8330ms
Retry Behavior.Does Not Retry On 400	✅	3508ms
Retry Behavior.Does Not Retry On 401	✅	3507ms
Retry Behavior.Respects Retry After Header	❌	7509ms
Retry Behavior.Implements Backoff	❌	20521ms
Deduplication.Generates Unique Uuids	✅	1495ms
Deduplication.Preserves Uuid On Retry	✅	6968ms
Deduplication.Different Events Have Different Uuids	✅	1503ms
Compression.Sends Gzip When Enabled	✅	1506ms
Batch Format.Uses Proper Batch Structure	✅	1507ms
Error Handling.Does Not Retry On 413	✅	3512ms
Error Handling.Retries On 408	❌	6505ms

Failures

retry_behavior.respects_retry_after_header

Retry delay too short: 999ms < 2500ms

retry_behavior.implements_backoff

First retry delay too short: 46ms < 100ms

error_handling.retries_on_408

Expected at least 2 requests, got 1

[eli-r-ph]

This LGTM

[github-actions]

posthog-python Compliance Report

Date: 2026-01-28 13:42:24 UTC
Duration: 144134ms

⚠️ Some Tests Failed

27/29 tests passed, 2 failed

---

Capture Tests

⚠️ 27/29 tests passed, 2 failed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	517ms
Format Validation.Event Has Uuid	✅	1507ms
Format Validation.Event Has Lib Properties	✅	1507ms
Format Validation.Distinct Id Is String	✅	1507ms
Format Validation.Token Is Present	✅	1507ms
Format Validation.Custom Properties Preserved	✅	1506ms
Format Validation.Event Has Timestamp	✅	1507ms
Retry Behavior.Retries On 503	✅	7970ms
Retry Behavior.Does Not Retry On 400	✅	3506ms
Retry Behavior.Does Not Retry On 401	✅	3508ms
Retry Behavior.Respects Retry After Header	❌	6629ms
Retry Behavior.Implements Backoff	✅	21129ms
Retry Behavior.Retries On 500	✅	6768ms
Retry Behavior.Retries On 502	✅	7117ms
Retry Behavior.Retries On 504	✅	7203ms
Retry Behavior.Max Retries Respected	✅	18778ms
Deduplication.Generates Unique Uuids	✅	1498ms
Deduplication.Preserves Uuid On Retry	✅	7472ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	13545ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	7314ms
Deduplication.No Duplicate Events In Batch	✅	1503ms
Deduplication.Different Events Have Different Uuids	✅	1507ms
Compression.Sends Gzip When Enabled	✅	1507ms
Batch Format.Uses Proper Batch Structure	✅	1506ms
Batch Format.Flush With No Events Sends Nothing	✅	1005ms
Batch Format.Multiple Events Batched Together	✅	1505ms
Error Handling.Does Not Retry On 403	✅	3507ms
Error Handling.Does Not Retry On 413	✅	3509ms
Error Handling.Retries On 408	❌	6511ms

Failures

retry_behavior.respects_retry_after_header

Retry delay too short: 122ms < 2500ms

error_handling.retries_on_408

Expected at least 2 requests, got 1