feat(error-tracking): standardize exception event metadata

[hpouillot]

💡 Motivation and Context

Standardize Flutter exception events across manual, framework, dispatcher, isolate, zone, aggregate, and web capture paths 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?

• flutter test test/dart_exception_processor_test.dart
• flutter analyze

📝 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 pnpm changeset to generate a changeset file

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Implemented with pi from the shared OpenSpec contract. Traversal is cycle-safe and bounded, with deterministic cause and aggregate-member relationships and explicit synthetic provenance.

[github-actions]

posthog-flutter Compliance Report

Date: 2026-08-26 08:27:27 UTC
Duration: 96784ms

✅ All Tests Passed!

45/45 tests passed

---

Capture Tests

✅ 29/29 tests passed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	140ms
Format Validation.Event Has Uuid	✅	119ms
Format Validation.Event Has Lib Properties	✅	116ms
Format Validation.Distinct Id Is String	✅	114ms
Format Validation.Token Is Present	✅	114ms
Format Validation.Custom Properties Preserved	✅	116ms
Format Validation.Event Has Timestamp	✅	118ms
Retry Behavior.Retries On 503	✅	5343ms
Retry Behavior.Does Not Retry On 400	✅	2117ms
Retry Behavior.Does Not Retry On 401	✅	2119ms
Retry Behavior.Respects Retry After Header	✅	8125ms
Retry Behavior.Implements Backoff	✅	15445ms
Retry Behavior.Retries On 500	✅	5224ms
Retry Behavior.Retries On 502	✅	5225ms
Retry Behavior.Retries On 504	✅	5224ms
Retry Behavior.Max Retries Respected	✅	15445ms
Deduplication.Generates Unique Uuids	✅	123ms
Deduplication.Preserves Uuid On Retry	✅	5223ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	10325ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	5230ms
Deduplication.No Duplicate Events In Batch	✅	122ms
Deduplication.Different Events Have Different Uuids	✅	115ms
Compression.Sends Gzip When Enabled	✅	115ms
Batch Format.Uses Proper Batch Structure	✅	113ms
Batch Format.Flush With No Events Sends Nothing	✅	109ms
Batch Format.Multiple Events Batched Together	✅	122ms
Error Handling.Does Not Retry On 403	✅	2115ms
Error Handling.Does Not Retry On 413	✅	2116ms
Error Handling.Retries On 408	✅	5224ms

Feature_Flags Tests

✅ 16/16 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	19ms
Request Payload.Flags Request Uses V2 Query Param	✅	10ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	9ms
Request Payload.Flags Request Omits Authorization Header	✅	9ms
Request Payload.Token In Flags Body Matches Init	✅	10ms
Request Payload.Groups Round Trip	✅	9ms
Request Payload.Groups Default To Empty Object	✅	8ms
Request Payload.Person Properties Distinct Id Auto Populated When Caller Omits It	✅	9ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	8ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	9ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	8ms
Request Lifecycle.No Flags Request On Init Alone	✅	5ms
Request Lifecycle.No Flags Request On Normal Capture	✅	112ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	14ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	9ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	114ms

[github-actions]

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