fix: keep flag payload reads out of only_accessed

[dustinbyrne]

💡 Motivation and Context

get_flag_payload/2 should be a silent payload lookup. Other server-side SDKs (Python/Node/PHP) document and implement payload reads as not counting for only_accessed, but the Elixir SDK was recording those reads as accesses. That meant only_accessed/1 could attach flags that code only fetched payloads for, not flags it branched on.

This aligns Elixir with the server-side SDK behavior by keeping get_flag_payload/2 out of the accessed set.

💚 How did you test it?

• mix format
• mix test
• mix credo --strict

📝 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 sampo add to generate a changeset file
  • Added .sampo/changesets/silent-payload-access.md manually because the sampo CLI is not installed locally.

[marandaneto]

merge #111 before

[github-actions]

posthog-elixir Compliance Report

Date: 2026-05-05 17:42:19 UTC
Duration: 107209ms

⚠️ Some Tests Failed

40/45 tests passed, 5 failed

---

Capture Tests

✅ 29/29 tests passed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	608ms
Format Validation.Event Has Uuid	✅	608ms
Format Validation.Event Has Lib Properties	✅	608ms
Format Validation.Distinct Id Is String	✅	608ms
Format Validation.Token Is Present	✅	607ms
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	✅	5614ms
Retry Behavior.Implements Backoff	✅	15625ms
Retry Behavior.Retries On 500	✅	5614ms
Retry Behavior.Retries On 502	✅	5615ms
Retry Behavior.Retries On 504	✅	5614ms
Retry Behavior.Max Retries Respected	✅	15624ms
Deduplication.Generates Unique Uuids	✅	617ms
Deduplication.Preserves Uuid On Retry	✅	5614ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	10618ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	5615ms
Deduplication.No Duplicate Events In Batch	✅	613ms
Deduplication.Different Events Have Different Uuids	✅	610ms
Compression.Sends Gzip When Enabled	✅	608ms
Batch Format.Uses Proper Batch Structure	✅	609ms
Batch Format.Flush With No Events Sends Nothing	✅	606ms
Batch Format.Multiple Events Batched Together	✅	612ms
Error Handling.Does Not Retry On 403	✅	2611ms
Error Handling.Does Not Retry On 413	✅	2610ms
Error Handling.Retries On 408	✅	5612ms

Feature_Flags Tests

⚠️ 11/16 tests passed, 5 failed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	❌	7ms
Request Payload.Flags Request Uses V2 Query Param	✅	5ms
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	❌	6ms
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	✅	6ms
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	✅	3ms
Request Lifecycle.No Flags Request On Normal Capture	✅	606ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	9ms
Request Lifecycle.Mock Response Value Is Returned To Caller	❌	6ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	❌	607ms

Failures

request_payload.request_with_person_properties_device_id

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

request_payload.token_in_flags_body_matches_init

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

request_payload.disable_geoip_omitted_defaults_to_false

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

request_lifecycle.mock_response_value_is_returned_to_caller

Last action result missing field 'value'. Keys: ['error', 'success']

side_effect_events.get_feature_flag_captures_feature_flag_called_event

Expected 1 events with name '$feature_flag_called', got 0

[dustinbyrne]

Noted, thanks — no code dependency from this branch, but happy to let #111 merge first.