fix: generate SDK UUIDs as v7

[marandaneto]

💡 Motivation and Context

SDK-generated IDs should be UUID v7 so event UUIDs, personless distinct IDs, and default AI trace IDs are time-ordered instead of random UUID v4 values.

This adds an internal UUID v7 helper that uses Guid.CreateVersion7() when the runtime provides it, with a fallback generator for older runtimes/target frameworks. The helper is used for runtime SDK-generated IDs in PostHog and PostHog.AI.

💚 How did you test it?

• dotnet test tests/UnitTests/UnitTests.csproj --filter "FullyQualifiedName~CapturedEventTests|FullyQualifiedName~PostHogContextTests"
• dotnet test tests/PostHog.AI.Tests/PostHog.AI.Tests.csproj --filter "FullyQualifiedName~PostHogOpenAIHandlerTests.SendAsyncCapturesEventOnSuccess"
• dotnet build src/PostHog/PostHog.csproj --no-restore
• dotnet build src/PostHog.AI/PostHog.AI.csproj --no-restore
• dotnet test PostHog.sln
• dotnet test
• dotnet format --verify-no-changes

📝 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 by the worker agent using repository-local inspection and .NET CLI validation. Follow-up review feedback added runtime use of Guid.CreateVersion7() when available plus deterministic fallback monotonicity coverage.

[github-actions]

posthog-dotnet Compliance Report

Date: 2026-06-19 11:43:40 UTC
Duration: 630ms

⚠️ Some Tests Failed

2/16 tests passed, 14 failed

---

Feature_Flags Tests

⚠️ 2/16 tests passed, 14 failed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	❌	44ms
Request Payload.Flags Request Uses V2 Query Param	❌	22ms
Request Payload.Flags Request Hits Flags Path Not Decide	❌	5ms
Request Payload.Flags Request Omits Authorization Header	❌	5ms
Request Payload.Token In Flags Body Matches Init	❌	5ms
Request Payload.Groups Round Trip	❌	5ms
Request Payload.Groups Default To Empty Object	❌	5ms
Request Payload.Person Properties Distinct Id Auto Populated When Caller Omits It	❌	5ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	❌	5ms
Request Payload.Disable Geoip Omitted Defaults To False	❌	4ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	❌	5ms
Request Lifecycle.No Flags Request On Init Alone	✅	4ms
Request Lifecycle.No Flags Request On Normal Capture	✅	184ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	❌	7ms
Request Lifecycle.Mock Response Value Is Returned To Caller	❌	5ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	❌	5ms

Failures

request_payload.request_with_person_properties_device_id

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.flags_request_uses_v2_query_param

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.flags_request_hits_flags_path_not_decide

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.flags_request_omits_authorization_header

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.token_in_flags_body_matches_init

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.groups_round_trip

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.groups_default_to_empty_object

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.person_properties_distinct_id_auto_populated_when_caller_omits_it

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.disable_geoip_false_propagates_as_geoip_disable_false

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.disable_geoip_omitted_defaults_to_false

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.flag_keys_to_evaluate_contains_only_requested_key

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_lifecycle.two_flag_calls_produce_two_remote_requests

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_lifecycle.mock_response_value_is_returned_to_caller

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

side_effect_events.get_feature_flag_captures_feature_flag_called_event

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

[greptile-apps]

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
src/PostHog/Library/UuidV7.cs:48-58
**Monotonicity not covered by any test**

The `IncrementRandom` counter is the whole reason this file exists rather than a simple `Guid.NewGuid()` wrapper — it ensures UUIDs generated in the same millisecond are still lexicographically ordered. But there is no test that actually exercises this path. A test that generates two UUIDs in rapid succession (spinning in a tight loop until two share the same millisecond) and then asserts `string.Compare(first, second) < 0` would give real confidence that the increment logic is correct. Without it, a future refactor of `IncrementRandom` could silently break the ordering guarantee and the existing test suite would not catch it.

_{Reviews (1): Last reviewed commit: "fix: generate SDK UUIDs as v7" | Re-trigger Greptile}