feat(flags): accept a caller default in FeatureFlagEvaluations#enabled?

[posthog]

💡 Motivation and Context

The cross-SDK is-feature-enabled spec states a hard requirement with no server-SDK carve-out:

The SDK SHALL accept a caller-supplied boolean default (defaultValue; parameter placement per platform idiom) and SHALL return it whenever the flag has no value: flags not loaded yet, a failed flags request, or no flag with that key in the loaded flags. A flag that has a value — including false and variant strings — always wins over the caller-supplied default.

The compliance matrix records this as a ❌ Fail for posthog-ruby:

FeatureFlagEvaluations#enabled? has no default_value parameter: def enabled?(key) ... flag&.enabled ? true : false end — it collapses every miss to a hardcoded false rather than accepting a caller override.

Remediation: Add a default_value: keyword to FeatureFlagEvaluations#enabled?, distinguishing "no default supplied" (current false behavior) from an explicit caller-supplied default.

Today a caller cannot tell "the flag is off" apart from "we never got an answer", and cannot choose to fail open when flag data is unavailable (empty snapshot, failed /flags request, quota-limited response).

Explanation of the change

PostHog::FeatureFlagEvaluations#enabled? gains an optional default_value: keyword:

flags = posthog.evaluate_flags(distinct_id)
flags.enabled?('new-checkout', default_value: true)

The default is returned only when the key is absent from the snapshot. Any flag that has a value — true, false, or a variant string — still wins over it, and nil (the parameter's own default) preserves the historical false result for a missing flag.

$feature_flag_called reporting is deliberately untouched: the event still carries the real evaluated response (nil plus $feature_flag_error: flag_missing for a miss), not the caller's default, so exposure data keeps reflecting what the server actually said.

Scope is limited to this one contract. The deprecated Client#is_feature_enabled has the same gap but is not changed here — it already warns callers to move to evaluate_flags(...).enabled?, which is now the compliant surface. The matrix's other open gaps for this SDK are left alone.

Why this is backwards-compatible

Purely additive. default_value: defaults to nil, and the miss path is only diverted when a caller explicitly passes a non-nil value, so every existing call site behaves exactly as before. public_api_snapshot.txt is regenerated to record the new optional keyword.

💚 How did you test it?

Four new specs in spec/posthog/feature_flag_evaluations_spec.rb, mapping onto the spec's acceptance scenarios (acceptance/public/is-feature-enabled.feature):

• a missing flag resolves to the caller default (true and false)
• an existing value wins over the default (disabled flag, variant flag, boolean flag)
• an empty snapshot uses the default, and still returns false when no default is given
• $feature_flag_called still reports the evaluated response and flag_missing, not the default

Locally, on Ruby 3.2:

• bundle exec rspec — 1252 examples, 0 failures (2 pending, the OTel-gemfile integration tests)
• bundle exec rubocop — 129 files, no offenses
• bundle exec rake public_api:check — clean after regenerating the snapshot

Follow-up work

• The same default-value gap is recorded for posthog-node, posthog-php, posthog-go and posthog-dotnet; posthog-java is the existing reference implementation.
• The spec's own "Surface variants" table shows a stale Ruby signature without a default parameter, and the docs for evaluate_flags could mention the new keyword.

📝 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: Fully autonomous

Opened by the scheduled SDK-compliance agent, which reads the compliance matrices in PostHog/sdk-specs and implements one open, backwards-compatible gap per run. This gap was picked over the alternatives because it is a hard SHALL with a one-method, additive remediation on a non-deprecated surface, and because no existing PR or branch in this repo touched it.

Deliberate decisions: only the canonical evaluate_flags(...).enabled? path was changed (the legacy is_feature_enabled is deprecated, so extending it would add API surface we are steering callers away from); $feature_flag_called properties were left reporting the true evaluated response rather than the substituted default, so the default cannot distort exposure analytics.

No manual/end-to-end testing beyond the automated checks listed above.

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Created with PostHog Desktop

🤖 Generated with Claude Code

[github-actions]

posthog-ruby-sync Compliance Report

Date: 2026-09-30T06:08:10.197599+00:00
Duration: 94306ms

⚠️ 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	✅	7ms
Format Validation.Event Has Lib Properties	✅	7ms
Format Validation.Distinct Id Is String	✅	10ms
Format Validation.Token Is Present	✅	8ms
Format Validation.Custom Properties Preserved	✅	7ms
Format Validation.Event Has Timestamp	✅	7ms
Format Validation.Non Utc Event Timestamp Is Converted To Utc	✅	8ms
Retry Behavior.Retries On 503	✅	5273ms
Retry Behavior.Does Not Retry On 400	✅	2010ms
Retry Behavior.Does Not Retry On 401	✅	2012ms
Retry Behavior.Respects Retry After Header	✅	8014ms
Retry Behavior.Implements Backoff	✅	15365ms
Retry Behavior.Retries On 500	✅	5115ms
Retry Behavior.Retries On 502	✅	5116ms
Retry Behavior.Retries On 504	✅	5163ms
Retry Behavior.Max Retries Respected	✅	15526ms
Deduplication.Generates Unique Uuids	✅	22ms
Deduplication.Preserves Uuid On Retry	✅	5162ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	10371ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	5163ms
Deduplication.No Duplicate Events In Batch	✅	19ms
Deduplication.Different Events Have Different Uuids	✅	9ms
Compression.Sends Gzip When Enabled	✅	6ms
Batch Format.Uses Proper Batch Structure	✅	7ms
Batch Format.Flush With No Events Sends Nothing	✅	3ms
Batch Format.Multiple Events Batched Together	❌	18ms
Error Handling.Does Not Retry On 403	✅	2009ms
Error Handling.Does Not Retry On 413	✅	2008ms
Error Handling.Retries On 408	✅	5156ms

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	✅	8ms
Request Payload.Token In Flags Body Matches Init	✅	9ms
Request Payload.Groups Round Trip	✅	8ms
Request Payload.Groups Default To Empty Object	✅	7ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	7ms
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	✅	3ms
Request Lifecycle.No Flags Request On Normal Capture	✅	6ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	9ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	6ms
Retry Behavior.Retries Flags On 502	✅	109ms
Retry Behavior.Retries Flags On 504	✅	157ms
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: 2026-09-30T06:08:20.856153+00:00
Duration: 98535ms

⚠️ 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	✅	109ms
Format Validation.Event Has Uuid	✅	105ms
Format Validation.Event Has Lib Properties	✅	108ms
Format Validation.Distinct Id Is String	✅	105ms
Format Validation.Token Is Present	✅	107ms
Format Validation.Custom Properties Preserved	✅	106ms
Format Validation.Event Has Timestamp	✅	106ms
Format Validation.Non Utc Event Timestamp Is Converted To Utc	✅	9ms
Retry Behavior.Retries On 503	✅	5310ms
Retry Behavior.Does Not Retry On 400	✅	2109ms
Retry Behavior.Does Not Retry On 401	✅	2108ms
Retry Behavior.Respects Retry After Header	✅	8115ms
Retry Behavior.Implements Backoff	✅	15723ms
Retry Behavior.Retries On 500	✅	5212ms
Retry Behavior.Retries On 502	✅	5211ms
Retry Behavior.Retries On 504	✅	5212ms
Retry Behavior.Max Retries Respected	✅	15713ms
Deduplication.Generates Unique Uuids	✅	112ms
Deduplication.Preserves Uuid On Retry	✅	5212ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	10313ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	5214ms
Deduplication.No Duplicate Events In Batch	✅	112ms
Deduplication.Different Events Have Different Uuids	✅	108ms
Compression.Sends Gzip When Enabled	✅	106ms
Batch Format.Uses Proper Batch Structure	✅	106ms
Batch Format.Flush With No Events Sends Nothing	✅	5ms
Batch Format.Multiple Events Batched Together	✅	110ms
Error Handling.Does Not Retry On 403	✅	2109ms
Error Handling.Does Not Retry On 413	✅	2107ms
Error Handling.Retries On 408	✅	5212ms

Feature_Flags Tests

⚠️ 16/17 tests passed, 1 failed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	108ms
Request Payload.Flags Request Uses V2 Query Param	✅	107ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	109ms
Request Payload.Flags Request Omits Authorization Header	✅	109ms
Request Payload.Token In Flags Body Matches Init	✅	107ms
Request Payload.Groups Round Trip	✅	108ms
Request Payload.Groups Default To Empty Object	✅	107ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	107ms
Request Payload.Disable Geoip Omitted Defaults To False	❌	107ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	108ms
Request Lifecycle.No Flags Request On Init Alone	✅	3ms
Request Lifecycle.No Flags Request On Normal Capture	✅	105ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	112ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	106ms
Retry Behavior.Retries Flags On 502	✅	210ms
Retry Behavior.Retries Flags On 504	✅	210ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	109ms

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']