feat(error-tracking): standardize exception event metadata

[hpouillot]

💡 Motivation and Context

Standardize Elixir exception events across Logger crash reports and Plug request boundaries with the cross-SDK metadata contract.

Canonical contract: https://github.com/PostHog/sdk-specs/blob/main/openspec/specs/exception-event-metadata/spec.md

💚 How did you test it?

• mix test test/posthog/handler_test.exs test/posthog/integrations/plug_test.exs: 61 passed
• mix format

📝 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 with pi from the shared OpenSpec contract. Logger crash events and Plug request failures now report stable boundary metadata without allowing generic context to overwrite canonical fields.

[github-actions]

posthog-elixir Compliance Report

Date: 2026-08-26 08:26:30 UTC
Duration: 117685ms

✅ 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	✅	610ms
Format Validation.Event Has Uuid	✅	610ms
Format Validation.Event Has Lib Properties	✅	610ms
Format Validation.Distinct Id Is String	✅	610ms
Format Validation.Token Is Present	✅	610ms
Format Validation.Custom Properties Preserved	✅	611ms
Format Validation.Event Has Timestamp	✅	610ms
Retry Behavior.Retries On 503	✅	5616ms
Retry Behavior.Does Not Retry On 400	✅	2614ms
Retry Behavior.Does Not Retry On 401	✅	2613ms
Retry Behavior.Respects Retry After Header	✅	5616ms
Retry Behavior.Implements Backoff	✅	15625ms
Retry Behavior.Retries On 500	✅	5615ms
Retry Behavior.Retries On 502	✅	5616ms
Retry Behavior.Retries On 504	✅	5615ms
Retry Behavior.Max Retries Respected	✅	15625ms
Deduplication.Generates Unique Uuids	✅	621ms
Deduplication.Preserves Uuid On Retry	✅	5615ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	10621ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	5620ms
Deduplication.No Duplicate Events In Batch	✅	615ms
Deduplication.Different Events Have Different Uuids	✅	612ms
Compression.Sends Gzip When Enabled	✅	610ms
Batch Format.Uses Proper Batch Structure	✅	609ms
Batch Format.Flush With No Events Sends Nothing	✅	607ms
Batch Format.Multiple Events Batched Together	✅	615ms
Error Handling.Does Not Retry On 403	✅	2613ms
Error Handling.Does Not Retry On 413	✅	2613ms
Error Handling.Retries On 408	✅	5614ms

Feature_Flags Tests

✅ 17/17 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	609ms
Request Payload.Flags Request Uses V2 Query Param	✅	610ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	609ms
Request Payload.Flags Request Omits Authorization Header	✅	610ms
Request Payload.Token In Flags Body Matches Init	✅	609ms
Request Payload.Groups Round Trip	✅	609ms
Request Payload.Groups Default To Empty Object	✅	609ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	609ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	610ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	609ms
Request Lifecycle.No Flags Request On Init Alone	✅	5ms
Request Lifecycle.No Flags Request On Normal Capture	✅	607ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	1216ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	609ms
Retry Behavior.Retries Flags On 502	✅	913ms
Retry Behavior.Retries Flags On 504	✅	912ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	1214ms