fix(flags): support JSON 3 response parsing

[dustinbyrne]

💡 Motivation and Context

JSON 3 rejects the positional options hash passed to JSON.parse in the shared feature-flag request path. In a fresh Rails 8.1 application this causes a successful remote flag evaluation to return nil; definition loading and remote config use the same parser.

Pass symbolize_names: true as keyword arguments, preserving existing JSON 2 behavior while supporting JSON 3. Add a public flag-evaluation regression test that calls the original parser and requires keyword options.

Includes patch changesets for both posthog-ruby and posthog-rails, so Rails users receive the fix through their exact core dependency pin. No public API or default changes.

💚 How did you test it?

• Regression test: fails before the fix, passes after.
• bundle exec rspec: 1,255 examples, 0 failures, 2 optional OpenTelemetry tests pending.
• Full suite with actual JSON 3.0.2 in a separate bundle: 1,255 examples, 0 failures, the same 2 pending.
• BUNDLE_GEMFILE=gemfiles/otel.gemfile bundle exec rspec: 1,255 examples, 0 failures, no pending.
• bundle exec rubocop: 129 files, no offenses.
• bundle exec rake public_api:check: passed.
• pnpm changeset status: both gems selected for patch releases.
• Built both gems from a disposable release simulation and verified the packaged Rails dependency pin. A fresh Rails 8.1.4 app with JSON 3.0.2 passed real-transport smoke tests against the local SDK mock server in sync and async modes, including remote flags, capture, automatic exceptions, ActiveJob, OTLP logs, flush, and shutdown.

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• Added patch changesets for Ruby and Rails.

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Implemented with pi using Git, Ruby/Bundler, Changesets, the SDK mock server, and GitHub CLI. A fresh, read-only pi reviewer found no issues.

[github-actions]

posthog-ruby-sync Compliance Report

Date: 2026-10-07T19:25:02.082576+00:00
Duration: 94031ms

⚠️ Some Tests Failed

45/47 tests passed, 2 failed

---

Capture Tests

⚠️ 29/30 tests passed, 1 failed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	10ms
Format Validation.Event Has Uuid	✅	6ms
Format Validation.Event Has Lib Properties	✅	6ms
Format Validation.Distinct Id Is String	✅	10ms
Format Validation.Token Is Present	✅	7ms
Format Validation.Custom Properties Preserved	✅	7ms
Format Validation.Event Has Timestamp	✅	7ms
Format Validation.Non Utc Event Timestamp Is Converted To Utc	✅	7ms
Retry Behavior.Retries On 503	✅	5248ms
Retry Behavior.Does Not Retry On 400	✅	2010ms
Retry Behavior.Does Not Retry On 401	✅	2011ms
Retry Behavior.Respects Retry After Header	✅	8015ms
Retry Behavior.Implements Backoff	✅	15357ms
Retry Behavior.Retries On 500	✅	5146ms
Retry Behavior.Retries On 502	✅	5151ms
Retry Behavior.Retries On 504	✅	5116ms
Retry Behavior.Max Retries Respected	✅	15461ms
Deduplication.Generates Unique Uuids	✅	22ms
Deduplication.Preserves Uuid On Retry	✅	5114ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	10353ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	5123ms
Deduplication.No Duplicate Events In Batch	✅	20ms
Deduplication.Different Events Have Different Uuids	✅	9ms
Compression.Sends Gzip When Enabled	✅	6ms
Batch Format.Uses Proper Batch Structure	✅	6ms
Batch Format.Flush With No Events Sends Nothing	✅	3ms
Batch Format.Multiple Events Batched Together	❌	17ms
Error Handling.Does Not Retry On 403	✅	2009ms
Error Handling.Does Not Retry On 413	✅	2010ms
Error Handling.Retries On 408	✅	5151ms

Failures

batch_format.multiple_events_batched_together

Expected 1 requests, got 5

Feature_Flags Tests

⚠️ 16/17 tests passed, 1 failed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	9ms
Request Payload.Flags Request Uses V2 Query Param	✅	7ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	7ms
Request Payload.Flags Request Omits Authorization Header	✅	6ms
Request Payload.Token In Flags Body Matches Init	✅	7ms
Request Payload.Groups Round Trip	✅	7ms
Request Payload.Groups Default To Empty Object	✅	7ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	9ms
Request Payload.Disable Geoip Omitted Defaults To False	❌	8ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	7ms
Request Lifecycle.No Flags Request On Init Alone	✅	3ms
Request Lifecycle.No Flags Request On Normal Capture	✅	7ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	8ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	7ms
Retry Behavior.Retries Flags On 502	✅	151ms
Retry Behavior.Retries Flags On 504	✅	111ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	8ms

Failures

request_payload.disable_geoip_omitted_defaults_to_false

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

[github-actions]

posthog-ruby-async Compliance Report

Date: 2026-10-07T19:25:04.676540+00:00
Duration: 98118ms

⚠️ Some Tests Failed

46/47 tests passed, 1 failed

---

Capture Tests

✅ 30/30 tests passed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	107ms
Format Validation.Event Has Uuid	✅	105ms
Format Validation.Event Has Lib Properties	✅	107ms
Format Validation.Distinct Id Is String	✅	105ms
Format Validation.Token Is Present	✅	106ms
Format Validation.Custom Properties Preserved	✅	106ms
Format Validation.Event Has Timestamp	✅	105ms
Format Validation.Non Utc Event Timestamp Is Converted To Utc	✅	8ms
Retry Behavior.Retries On 503	✅	5409ms
Retry Behavior.Does Not Retry On 400	✅	2108ms
Retry Behavior.Does Not Retry On 401	✅	2107ms
Retry Behavior.Respects Retry After Header	✅	8015ms
Retry Behavior.Implements Backoff	✅	15520ms
Retry Behavior.Retries On 500	✅	5211ms
Retry Behavior.Retries On 502	✅	5212ms
Retry Behavior.Retries On 504	✅	5211ms
Retry Behavior.Max Retries Respected	✅	15521ms
Deduplication.Generates Unique Uuids	✅	109ms
Deduplication.Preserves Uuid On Retry	✅	5210ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	10416ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	5213ms
Deduplication.No Duplicate Events In Batch	✅	110ms
Deduplication.Different Events Have Different Uuids	✅	107ms
Compression.Sends Gzip When Enabled	✅	106ms
Batch Format.Uses Proper Batch Structure	✅	105ms
Batch Format.Flush With No Events Sends Nothing	✅	3ms
Batch Format.Multiple Events Batched Together	✅	108ms
Error Handling.Does Not Retry On 403	✅	2107ms
Error Handling.Does Not Retry On 413	✅	2107ms
Error Handling.Retries On 408	✅	5211ms

Feature_Flags Tests

⚠️ 16/17 tests passed, 1 failed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	106ms
Request Payload.Flags Request Uses V2 Query Param	✅	106ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	106ms
Request Payload.Flags Request Omits Authorization Header	✅	105ms
Request Payload.Token In Flags Body Matches Init	✅	109ms
Request Payload.Groups Round Trip	✅	105ms
Request Payload.Groups Default To Empty Object	✅	106ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	105ms
Request Payload.Disable Geoip Omitted Defaults To False	❌	106ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	105ms
Request Lifecycle.No Flags Request On Init Alone	✅	3ms
Request Lifecycle.No Flags Request On Normal Capture	✅	104ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	110ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	106ms
Retry Behavior.Retries Flags On 502	✅	236ms
Retry Behavior.Retries Flags On 504	✅	207ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	107ms

Failures

request_payload.disable_geoip_omitted_defaults_to_false

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

[greptile-apps]

[Medium risk] Fixes feature flag response parsing for JSON 3 compatibility.

The PR appears safe to merge; no actionable issues were found.

_{Reviews (1) · Last reviewed commit: "fix(flags): support JSON 3 response pars..." · Reviewed by Greptile}