[eli-r-ph]

💡 Motivation and Context

The v2 migration guide and the capture-v1-default changeset say feature flag properties ($feature/<key>, $active_feature_flags) win over the request context and DefaultEventProperties. The code does the opposite, and that is the intended order: flag properties are values the SDK adds, so the request context and DefaultEventProperties win over them, and the event's own Properties win over everything (posthog.go fills context and defaults before both flag paths; TestEventPropertyLayers pins it).

This order matches posthog-go 1.x, posthog-python and posthog-node, which all let context and default properties win over flag properties, and the client SDK order in PostHog/sdk-specs#143. posthog-python's v1 branch gets the same fix in PostHog/posthog-python#1121.

• docs/migration-v2.md lists flag properties from a Flags snapshot or SendFeatureFlags with the other SDK-added values, which fill under the event, the request context and DefaultEventProperties.
• The capture-v1-default changeset says the same.

💚 How did you test it?

Docs only. go test -run TestEventPropertyLayers passes and pins the described order.

📝 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 (edited the existing capture-v1-default changeset instead)

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Authored with Claude Code (Claude Opus 5.5), directed by @eli-r-ph.

🤖 Generated with Claude Code