[turnipdabeets]

💡 Motivation and Context

Part of the 4.0 stack on #871. Removes defaultValue from the client getFeatureFlag:

// before
getFeatureFlag(key: String, defaultValue: Any? = null, sendFeatureFlagEvent: Boolean? = null): Any?
// after
getFeatureFlag(key: String, sendFeatureFlagEvent: Boolean? = null): Any?

Migration: getFeatureFlag(key, default) becomes getFeatureFlag(key) ?: default.

Why:

• The canonical client signature in sdk-specs has no default, and iOS, Flutter and React Native don't have one.
• A fallback was sent as $feature_flag_response in $feature_flag_called, so it could be reported as the flag's value.

What upgraders should watch for:

Before	After
Disabled SDK returned defaultValue	Returns null
getFeatureFlag("key", "fallback")	Stops compiling
getFeatureFlag("key", true)	Still compiles, but true now means sendFeatureFlagEvent
isFeatureEnabled("missing", true) reported true in $feature_flag_called	Still returns true, but reports an empty response

The last row is a side effect: isFeatureEnabled goes through getFeatureFlag. Its defaultValue parameter and return value don't change, as the spec requires. It's the same reporting problem, so I didn't add code to preserve it.

Not changed: getFeatureFlagStateless, posthog-server, and PostHogRemoteConfig.getFeatureFlag, which keeps its own defaultValue.

In-repo callers: no production code passed a default. Only isFeatureEnabled and the static PostHog.getFeatureFlag forwarded it. The Flutter and KMP Android code doesn't pass one either.

💚 How did you test it?

• ./gradlew :posthog:test :posthog-android:testReleaseUnitTest :posthog-server:test :posthog-server-openfeature:test :posthog-android-surveys-compose:testDebugUnitTest apiCheck spotlessCheck with the samples compiled: everything passed except one posthog-android test in that run, PostHogReplayIntegrationTest > bitmap allocation failure feeds the discard counter. It then passed 3 reruns of its class and 3 full reruns of the module, and it doesn't touch flags, so it looks flaky. I didn't find the cause.
• Replaced the test that expected the default in the event. New tests cover: a missing flag returns null, a default isn't reported from either API, a false flag beats the default, and a disabled SDK returns null / the default.
• Checked the new tests with 4 temporary mutations (dropping the disabled guard, leaking a fallback, dropping ?: defaultValue, ignoring the flag value). Each one failed the expected tests.

📝 Checklist

• All commits are signed (see Commit signing)
• 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: Human-driven (agent-assisted)

Claude Code (Claude Opus 5.5) made the change, updated callers and the API dump, and ran the tests. A dry-run merge with #881 is clean. No device or manual testing.

🤖 Generated with Claude Code

[marandaneto]

The code looks good; no qualifying findings. Verdict: correct.