fix: include group context in $feature_flag_called dedupe key

[gustavohstrassburger]

💡 Motivation and Context

In captureFlagCalledIfNeeded (posthog.go), the per-distinct_id LRU dedupe key only included (distinct_id, flag_key, device_id). For group-scoped flags this meant that when the same user was evaluated under a different group, no new $feature_flag_called event was fired — causing per-group exposure undercount for experiments scoped to a group key.

Mirrors the posthog-node fix in PostHog/posthog-js#3658 (which closes PostHog/posthog-js#3651). Both SDKs share the same dedupe shape, so backend evaluation needs the same change.

💚 How did you test it?

Added three table-style tests in feature_flag_evaluations_test.go:

• TestCaptureFlagCalled_FiresPerGroupContext — same user, same flag, two different group contexts → two events fired, both $groups payloads observed.
• TestCaptureFlagCalled_DedupesAcrossRepeatedCallsUnderSameGroup — repeated access under the same group → one event.
• TestCaptureFlagCalled_DedupesAcrossGroupKeyOrder — same groups passed with different Go map insertion order → still one event (canonicalized by sort.Strings + JSON encode).

go test -count=1 ./... is green.

📝 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

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Created with PostHog Code

[github-actions]

posthog-go Compliance Report

Date: 2026-05-28 15:32:17 UTC
Duration: 107265ms

⚠️ Some Tests Failed

39/45 tests passed, 6 failed

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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	✅	608ms
Format Validation.Event Has Lib Properties	✅	608ms
Format Validation.Distinct Id Is String	✅	607ms
Format Validation.Token Is Present	✅	608ms
Format Validation.Custom Properties Preserved	✅	608ms
Format Validation.Event Has Timestamp	✅	608ms
Retry Behavior.Retries On 503	✅	5613ms
Retry Behavior.Does Not Retry On 400	✅	2610ms
Retry Behavior.Does Not Retry On 401	✅	2610ms
Retry Behavior.Respects Retry After Header	✅	5613ms
Retry Behavior.Implements Backoff	✅	15623ms
Retry Behavior.Retries On 500	✅	5612ms
Retry Behavior.Retries On 502	✅	5613ms
Retry Behavior.Retries On 504	✅	5612ms
Retry Behavior.Max Retries Respected	✅	15623ms
Deduplication.Generates Unique Uuids	✅	617ms
Deduplication.Preserves Uuid On Retry	✅	5613ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	10618ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	5613ms
Deduplication.No Duplicate Events In Batch	✅	612ms
Deduplication.Different Events Have Different Uuids	✅	610ms
Compression.Sends Gzip When Enabled	✅	608ms
Batch Format.Uses Proper Batch Structure	✅	608ms
Batch Format.Flush With No Events Sends Nothing	✅	605ms
Batch Format.Multiple Events Batched Together	✅	612ms
Error Handling.Does Not Retry On 403	✅	2610ms
Error Handling.Does Not Retry On 413	✅	2610ms
Error Handling.Retries On 408	✅	5612ms

Feature_Flags Tests

⚠️ 10/16 tests passed, 6 failed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	❌	9ms
Request Payload.Flags Request Uses V2 Query Param	✅	6ms
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	✅	6ms
Request Payload.Groups Round Trip	✅	6ms
Request Payload.Groups Default To Empty Object	✅	6ms
Request Payload.Person Properties Distinct Id Auto Populated When Caller Omits It	❌	6ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	❌	6ms
Request Payload.Disable Geoip Omitted Defaults To False	❌	6ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	❌	7ms
Request Lifecycle.No Flags Request On Init Alone	✅	4ms
Request Lifecycle.No Flags Request On Normal Capture	✅	607ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	9ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	5ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	❌	610ms

Failures

request_payload.request_with_person_properties_device_id

Field 'distinct_id' not found in /flags request body at path 'person_properties.distinct_id'. Available keys: ['$device_id']

request_payload.person_properties_distinct_id_auto_populated_when_caller_omits_it

Field 'distinct_id' not found in /flags request body at path 'person_properties.distinct_id'. Available keys: ['email']

request_payload.disable_geoip_false_propagates_as_geoip_disable_false

Expected geoip_disable=False, got True

request_payload.disable_geoip_omitted_defaults_to_false

Expected geoip_disable=False, got True

request_payload.flag_keys_to_evaluate_contains_only_requested_key

Field 'flag_keys_to_evaluate' not found in /flags request body at path 'flag_keys_to_evaluate'. Available keys: ['api_key', 'distinct_id', 'groups', 'person_properties', 'group_properties', 'geoip_disable']

side_effect_events.get_feature_flag_captures_feature_flag_called_event

Expected 1 events with name '$feature_flag_called', got 2

[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.

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### Issue 1 of 1
feature_flag_evaluations_test.go:693-761
**Tests 2 and 3 should be combined into a single table-driven test**

The PR description calls these "table-style tests," but `TestCaptureFlagCalled_DedupesAcrossRepeatedCallsUnderSameGroup` and `TestCaptureFlagCalled_DedupesAcrossGroupKeyOrder` are structurally identical — both set up a fresh client, issue 2-3 calls that should produce exactly one `$feature_flag_called` event, sleep, and assert on the count. Prefer a single parameterised test using `t.Run` subtests with a cases slice (e.g. `{name, calls []Groups}`) so the boilerplate is stated once and both scenarios stay together.

_{Reviews (1): Last reviewed commit: "chore: add changeset" | Re-trigger Greptile}