[eli-r-ph]

Stacked on #315.

💡 Motivation and Context

A request context $set is a default for every event in the request. Today it is used only when the event has no $set at all, so an event that sets one person property loses every context person property. The other v1 server SDKs fill these properties key by key (posthog-python, posthog-go and posthog-node).

Changes

• A $set, $set_once, $groups or $group_set from the request context fills in only the keys the event's own value lacks. The event wins for each key it sets, and a non-object value on either side keeps the event's value whole.
• The same fill applies to exception properties from exception_options and the scoped context.
• $feature_flag_called events fill the request context before the client's $is_server and $geoip_disable defaults, so the context wins there as on other events. A per-call disable_geoip still wins over the context.
• Breaking: the request context shipped in 0.28.0 with whole-value fill. The migration guide and a changeset describe the change.

💚 How did you test it?

• The flag snapshot test now sets $is_server: false in the context and checks the flag event keeps it; it fails with the old order.
• test_request_context and a new exception_options unit test check a context $set of {plan: free, source: web} under an event $set of {plan: pro} sends {plan: pro, source: web}. Both fail with the old fill.
• cargo test --all-features (619 passed) and --no-default-features --features error-tracking,tls (480 passed), cargo clippy --tests -- -D warnings (with and without mcp), cargo fmt -- --check, scripts/check-public-api.sh (no API change).

📝 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 sampo add to generate a changeset file

🤖 Generated with Claude Code

[marandaneto]

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