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-elixir Compliance Report

Date: 2026-01-28 13:53:10 UTC
Duration: 105839ms

⚠️ Some Tests Failed

15/29 tests passed, 14 failed

---

Capture Tests

⚠️ 15/29 tests passed, 14 failed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	609ms
Format Validation.Event Has Uuid	❌	609ms
Format Validation.Event Has Lib Properties	✅	609ms
Format Validation.Distinct Id Is String	✅	609ms
Format Validation.Token Is Present	✅	609ms
Format Validation.Custom Properties Preserved	✅	609ms
Format Validation.Event Has Timestamp	✅	609ms
Retry Behavior.Retries On 503	❌	5614ms
Retry Behavior.Does Not Retry On 400	✅	2611ms
Retry Behavior.Does Not Retry On 401	✅	2612ms
Retry Behavior.Respects Retry After Header	❌	5609ms
Retry Behavior.Implements Backoff	❌	15616ms
Retry Behavior.Retries On 500	❌	5615ms
Retry Behavior.Retries On 502	❌	5615ms
Retry Behavior.Retries On 504	❌	5615ms
Retry Behavior.Max Retries Respected	❌	15624ms
Deduplication.Generates Unique Uuids	✅	620ms
Deduplication.Preserves Uuid On Retry	❌	5615ms
Deduplication.Preserves Uuid And Timestamp On Retry	❌	10620ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	❌	5614ms
Deduplication.No Duplicate Events In Batch	✅	615ms
Deduplication.Different Events Have Different Uuids	❌	612ms
Compression.Sends Gzip When Enabled	❌	609ms
Batch Format.Uses Proper Batch Structure	✅	609ms
Batch Format.Flush With No Events Sends Nothing	✅	606ms
Batch Format.Multiple Events Batched Together	✅	613ms
Error Handling.Does Not Retry On 403	✅	2611ms
Error Handling.Does Not Retry On 413	✅	2611ms
Error Handling.Retries On 408	❌	5614ms

Failures

format_validation.event_has_uuid

Event missing 'uuid' field

retry_behavior.retries_on_503

Expected at least 3 requests, got 1

retry_behavior.respects_retry_after_header

Expected at least 2 requests, got 1

retry_behavior.implements_backoff

Expected at least 3 requests, got 1

retry_behavior.retries_on_500

Expected at least 2 requests, got 1

retry_behavior.retries_on_502

Expected at least 2 requests, got 1

retry_behavior.retries_on_504

Expected at least 2 requests, got 1

retry_behavior.max_retries_respected

Expected 4 requests, got 1

deduplication.preserves_uuid_on_retry

Need at least 2 requests to check retry

deduplication.preserves_uuid_and_timestamp_on_retry

Expected at least 3 requests, got 1

deduplication.preserves_uuid_and_timestamp_on_batch_retry

Expected at least 2 requests, got 1

deduplication.different_events_have_different_uuids

Need at least 2 events

compression.sends_gzip_when_enabled

Header 'Content-Encoding' with value 'gzip' not found in requests

error_handling.retries_on_408

Expected at least 2 requests, got 1

[rafaeelaudibert]

There's a simple way to implement this, but I don't think it's a big deal to change that now. You can just hook on the Reqand collect the requests. It's very similar to how we do LLM Analytics here.