Fix the latest status rollup per user

Agent-written pipeline PRs keep using a DISTINCT ON query to keep the latest event per user, with a LIMIT 1000 that quietly drops users. You want one plain function to check those queries against.

An assistant wrote latest_status_per_user(rows). It is in the editor. It has a bug. Find it and fix it.

Input and output:

• rows: event rows, each "user_id|status|updated_at". updated_at is an ISO date such as 2026-03-04, or empty when the database holds NULL.
• Return one "user_id=status" string per user.

Rules the tests check:

• Skip a row that does not split on | into exactly 3 fields.
• For each user, keep the row with the latest updated_at. Compare the dates as plain strings.
• An empty updated_at is older than every real date, as NULLS LAST orders it. A row with an empty date still counts: a user whose rows all have empty dates is still in the output.
• On a tie, keep the row that came first.
• Every user appears, with no cap on the count. Sort the output by user id, in ascending order by plain string comparison.