Write a SQL query to measure the performance of a free-month promotion experiment. Assume `experiment_users` already contains only users who were eligible for the experiment. Do not re-implement eligibility logic. Tables: 1. `experiment_users` - `user_id` BIGINT -- primary key - `variant` VARCHAR -- values: `control`, `free_month` - `assigned_at` TIMESTAMP -- experiment assignment time in UTC 2. `subscription_events` - `user_id` BIGINT -- foreign key to `experiment_users.user_id` - `event_ts` TIMESTAMP -- event time in UTC - `event_type` VARCHAR -- one of `signup`, `free_trial_start`, `paid_start`, `cancel`, `reactivate` Business definitions: - `eligible_users`: distinct users in `experiment_users`. - `signups_30d`: users whose first `signup` after `assigned_at` occurs within 30 days of assignment. - `paid_converted_60d`: users whose first `paid_start` after `assigned_at` occurs within 60 days of assignment. - `churned_90d_after_first_paid`: among users with a first `paid_start`, count users who have at least one `cancel` event within 90 days after that first `paid_start`. - A user may cancel, reactivate, and cancel again. Count the user at most once, using the first `cancel` after the first `paid_start`. Ignore `cancel` events that happen before the first `paid_start`. - Use only each user's first qualifying `signup` and first qualifying `paid_start` after assignment. Return one row per `variant` with these columns: - `variant` - `eligible_users` - `signups_30d` - `paid_converted_60d` - `churned_90d_after_first_paid` - `churn_rate_90d_after_first_paid` where the denominator is `paid_converted_60d`.