fix(server): include group context in $feature_flag_called dedupe key

[gustavohstrassburger]

💡 Motivation and Context

In PostHogFeatureFlagCalledCache.add, the per-distinctId LRU dedupe key only included (distinctId, flagKey, value). 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.

This affects two modules:

• posthog/ (PostHogStateless / cache) — captureFeatureFlagCalledEvent now takes an optional groups parameter (added via @JvmOverloads so the existing Java-callable signature still exists). The cache key gets a canonical groupsRepr built from the sorted entries so two equal maps with keys in a different insertion order still dedupe.
• posthog-server/ — PostHogFeatureFlagEvaluations now carries the groups it was evaluated under and passes them to the host's dedup-aware capture call.

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 4 new tests in PostHogFeatureFlagCalledCacheTest and 1 in PostHogFeatureFlagEvaluationsTest:

Cache-level (posthog/):

• same flag and value with different group contexts are tracked separately — two cache entries.
• same flag and value with same group context dedupe — one cache entry.
• same flag and value with same groups in different key order dedupe — one cache entry (canonicalized).
• null vs empty vs unset groups all dedupe to no-group bucket — single entry covers all three.

Snapshot-level (posthog-server/):

• isEnabled propagates groups to the host so dedup can include group context — confirms the snapshot threads its evaluation groups through to the host's capture call.

./gradlew :posthog:test :posthog-server:test is green; ./gradlew :posthog:apiDump :posthog-server:apiDump regenerated the public .api files.

📝 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-android Compliance Report

Date: 2026-05-27 19:01:48 UTC
Duration: 2829ms

⚠️ Some Tests Failed

0/16 tests passed, 16 failed

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Feature_Flags Tests

⚠️ 0/16 tests passed, 16 failed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	❌	292ms
Request Payload.Flags Request Uses V2 Query Param	❌	34ms
Request Payload.Flags Request Hits Flags Path Not Decide	❌	30ms
Request Payload.Flags Request Omits Authorization Header	❌	24ms
Request Payload.Token In Flags Body Matches Init	❌	22ms
Request Payload.Groups Round Trip	❌	18ms
Request Payload.Groups Default To Empty Object	❌	15ms
Request Payload.Person Properties Distinct Id Auto Populated When Caller Omits It	❌	16ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	❌	18ms
Request Payload.Disable Geoip Omitted Defaults To False	❌	15ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	❌	16ms
Request Lifecycle.No Flags Request On Init Alone	❌	10ms
Request Lifecycle.No Flags Request On Normal Capture	❌	2047ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	❌	14ms
Request Lifecycle.Mock Response Value Is Returned To Caller	❌	12ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	❌	15ms

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.no_flags_request_on_init_alone

Expected 0 /flags requests, got 1

request_lifecycle.no_flags_request_on_normal_capture

Expected 0 /flags requests, got 1

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 2 code review issues. Work through them one at a time, proposing concise fixes.

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### Issue 1 of 2
posthog/src/main/java/com/posthog/internal/PostHogFeatureFlagCalledCache.kt:146-155
**Unsafe separator in canonical representation can cause hash collisions**

The `=` and `;` separators used to build the canonical key are not escaped, so a group value that embeds `;key2=val2` can produce the same string as a genuinely different two-entry map. Concretely, `mapOf("a" to "b;c=d", "e" to "f")` and `mapOf("a" to "b", "c" to "d", "e" to "f")` both encode to `"a=b;c=d;e=f;"` — two distinct group contexts that should fire separate events would instead silently dedupe to one. A safer encoding (e.g., percent-encoding keys and values before concatenating) eliminates the ambiguity.

### Issue 2 of 2
posthog/src/test/java/com/posthog/internal/PostHogFeatureFlagCalledCacheTest.kt:289-299
**Prefer a parameterised test for the "no-group bucket" coverage**

The `null vs empty vs unset groups all dedupe to no-group bucket` test calls `add` three times in sequence on a shared cache, which means only the first call returns `true` — the second and third could be returning `false` because the key is identical rather than because `null`/`emptyMap()` canonicalize the same way. A `@ParameterizedTest` with three independent caches (or three separate assertions from a fresh cache each time) would make the intent clearer and catch a regression where one variant encodes differently.

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

[ioannisj]

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