WAL Log Enrichment

A service replays its write-ahead log (WAL) to rebuild an analytics table. Because of retries, the same log sequence number (LSN) can be delivered more than once, and entries can arrive out of order.

• entries is a list of [lsn, user_id, action] rows in arrival order (lsn is an integer; user_id and action are strings).
• profiles is a list of [user_id, tier] rows. If a user appears more than once, the last row for that user is the current tier.

Build the cleaned log:

1. For each lsn, keep only the first entry that arrived with it; later entries with the same lsn are discarded, even if their contents differ.
2. Append the user's tier to each kept entry, giving [lsn, user_id, action, tier]. Use the string "unknown" if the user has no profile.
3. Return the rows sorted by increasing lsn.