[posthog]

💡 Motivation and Context

Contract: is-feature-enabled — "Canonical is-feature-enabled behavior".

The SDK SHALL accept a caller-supplied boolean default (defaultValue) 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 posthog-dotnet compliance matrix records this as ❌ Fail (note n20):

FeatureFlagEvaluations.IsEnabled(key) returns record is { Enabled: true } — a genuinely-disabled flag and a flag with no value at all are indistinguishable, and there is no way for a caller to override a miss to true.

Remediation: Add FeatureFlagEvaluations.IsEnabled(string key, bool defaultValue) that returns defaultValue only on a genuine miss, distinguishing it from a real false result.

Other SDKs already have this: posthog-ruby (#285), posthog-js/node (#4484), posthog-go (#349).

🔨 What changed

• New overload FeatureFlagEvaluations.IsEnabled(string key, bool defaultValue). It still records snapshot access and fires $feature_flag_called exactly as before, then returns record is null ? defaultValue : record.Enabled.
• The existing IsEnabled(string key) now delegates with defaultValue: false, so a present-but-disabled flag returns false and a missing flag returns false — byte-for-byte the old behavior.

Why this is backwards-compatible

It is purely additive via C# overloading. No existing signature, return type, or value changes: the one-argument overload's observable behavior is identical, and the new overload only exists once a caller opts in by passing a default. The PublicAPI.Unshipped.txt diff is a single added line.

💚 How did you test it?

• Added three cases to TheSnapshotAccessMethods in tests/UnitTests/Features/FeatureFlagEvaluationsTests.cs, mirroring the spec's scenarios: a missing flag resolves to the caller default (false and true), and a present false / variant-a flag wins over an opposing default.
• The existing UnknownKeyReturnsFalsyValue test continues to pin the no-default behavior.
• dotnet test tests/UnitTests/UnitTests.csproj — 1239 passed / 0 failed on net8.0, 1229 passed / 0 failed on netcoreapp3.1.
• Added a minor changeset for PostHog.

📝 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

👣 Follow-up work (not in this PR)

Compliance note n20 also flags that IsFeatureEnabledAsync(featureKey, distinctId, options) has no defaultValue on its options object, and that an XML doc on a bool?-returning extension overload claims null-on-miss semantics it does not implement. Both were left out to keep this change to the single canonical surface; they are worth a separate pass.

🤖 Agent context

Autonomy: Fully autonomous

Opened by a scheduled PostHog agent run that reads the PostHog/sdk-specs compliance matrices and implements one backwards-compatible gap per run. This gap was picked over the other open posthog-dotnet gaps because it is a hard SHALL on a widely-used, user-facing flag API, the remediation is concrete and self-contained, and the fix is additive. Candidates in other SDKs for the same contract were skipped as already merged or in flight. Verified locally with the repo's unit test suite; no manual/integration testing was performed.

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Created with PostHog Desktop

🤖 Generated with Claude Code

[github-actions]

posthog-dotnet Compliance Report

Date: 2026-10-11T06:09:28.797632+00:00
Duration: 125036ms

✅ All Tests Passed!

47/47 tests passed

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Capture Tests

✅ 30/30 tests passed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	264ms
Format Validation.Event Has Uuid	✅	129ms
Format Validation.Event Has Lib Properties	✅	116ms
Format Validation.Distinct Id Is String	✅	115ms
Format Validation.Token Is Present	✅	111ms
Format Validation.Custom Properties Preserved	✅	118ms
Format Validation.Event Has Timestamp	✅	111ms
Format Validation.Non Utc Event Timestamp Is Converted To Utc	✅	123ms
Retry Behavior.Retries On 503	✅	8124ms
Retry Behavior.Does Not Retry On 400	✅	2118ms
Retry Behavior.Does Not Retry On 401	✅	2114ms
Retry Behavior.Respects Retry After Header	✅	8119ms
Retry Behavior.Implements Backoff	✅	22133ms
Retry Behavior.Retries On 500	✅	6118ms
Retry Behavior.Retries On 502	✅	6118ms
Retry Behavior.Retries On 504	✅	6114ms
Retry Behavior.Max Retries Respected	✅	22136ms
Deduplication.Generates Unique Uuids	✅	118ms
Deduplication.Preserves Uuid On Retry	✅	6118ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	13119ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	6120ms
Deduplication.No Duplicate Events In Batch	✅	116ms
Deduplication.Different Events Have Different Uuids	✅	111ms
Compression.Sends Gzip When Enabled	✅	109ms
Batch Format.Uses Proper Batch Structure	✅	109ms
Batch Format.Flush With No Events Sends Nothing	✅	105ms
Batch Format.Multiple Events Batched Together	✅	115ms
Error Handling.Does Not Retry On 403	✅	2112ms
Error Handling.Does Not Retry On 413	✅	2111ms
Error Handling.Retries On 408	✅	6118ms

Feature_Flags Tests

✅ 17/17 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	150ms
Request Payload.Flags Request Uses V2 Query Param	✅	110ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	110ms
Request Payload.Flags Request Omits Authorization Header	✅	110ms
Request Payload.Token In Flags Body Matches Init	✅	111ms
Request Payload.Groups Round Trip	✅	114ms
Request Payload.Groups Default To Empty Object	✅	110ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	111ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	111ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	110ms
Request Lifecycle.No Flags Request On Init Alone	✅	4ms
Request Lifecycle.No Flags Request On Normal Capture	✅	108ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	215ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	113ms
Retry Behavior.Retries Flags On 502	✅	1116ms
Retry Behavior.Retries Flags On 504	✅	1113ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	213ms

[ioannisj]

🤖 An AI agent wrote this on behalf of @ioannisj.

⚠️ PUBLIC API CHANGE
FeatureFlagEvaluations.IsEnabled(string key, bool defaultValue) — added (src/PostHog/Features/FeatureFlagEvaluations.cs:95)
Changeset level: minor

Checked the miss paths (unknown key, a failed /flags request, a per-flag failed: true) against posthog-js node's isEnabled(key, { defaultValue }). Same semantics, $feature_flag_called still fires on a miss, and the one-arg IsEnabled(key) behaves exactly as before, so nothing to fix from my side.

One small thing for whoever touches this file next: the <see cref="IsEnabled"/> in the OnlyAccessed doc is now ambiguous between the two overloads. It only warns (CS0419) when XML docs get generated, which we don't do today, so IsEnabled(string) would pin it as a drive-by.