fix: add feature flag retry circuit breaker

[marandaneto]

💡 Motivation and Context

Stacked on top of #245 to prototype a circuit breaker for /flags retry behavior in a multithreaded/stateless SDK.

The existing retry is bounded per call, but during a broad connectivity issue many concurrent request threads can each sleep and retry independently. This adds a shared circuit breaker so repeated transient /flags transport failures put the SDK into a short cooldown and subsequent calls fail fast instead of all sleeping/retrying.

💚 How did you test it?

• dotnet test tests/UnitTests/UnitTests.csproj --filter FullyQualifiedName~HttpClientExtensionsTests
• git diff --check

📝 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 as a draft stacked PR for review. The circuit opens after consecutive transient /flags failures, fails fast during cooldown, and allows a half-open probe after cooldown. HTTP/API status failures remain non-retryable and do not trip the transient-failure circuit.

[github-actions]

posthog-dotnet Compliance Report

Date: 2026-06-27 10:48:18 UTC
Duration: 607ms

⚠️ 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	❌	47ms
Request Payload.Flags Request Uses V2 Query Param	❌	23ms
Request Payload.Flags Request Hits Flags Path Not Decide	❌	6ms
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	❌	5ms
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	✅	188ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	❌	8ms
Request Lifecycle.Mock Response Value Is Returned To Caller	❌	6ms
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'

[marandaneto]

@haacked wdyt about this circuit break approach? (we can also make the 30s configurable)

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix: add feature flag retry circuit brea..." | Re-trigger Greptile}

[haacked]

@marandaneto I meant to submit the review as a comment, not approval! But I trust you to do the right thing. 😄

[marandaneto]

@marandaneto I meant to submit the review as a comment, not approval! But I trust you to do the right thing. 😄

thx for the review, yeah it was just a draft with a concept, will check and work on it on monday, then i can port this change across other sdks that have a similar situation

[marandaneto]

i re-requested review to remove the approval, but no need to re-review until i address the comments and make it ready for review