Follow-up to the previous commit. Replace the post-fetch Python re-sort (which
required dropping LIMIT/OFFSET from SQL and scanning every session row) with a
recursive CTE that walks compression-continuation chains and computes
effective_last_active per root at SQL level. The outer query can then ORDER BY
+ LIMIT efficiently, and the Python projection loop no longer has to handle
ordering.
This preserves the correctness win (old compression roots whose live tip was
touched recently surface correctly) without the O(N) scan, which matters for
users with thousands of sessions.
Adds a regression test pinning the compression-tip case at limit=1 — the
stress case that any bounded-oversample shortcut would get wrong.
Co-authored-by: simbam99 <simbamax99@gmail.com>
5089c55e0b