LEASE_CAPTURE_ONLY: group leases of the corpus windows' ranges only

The lease bounds alone don't select a window: the history planner's oldest
buckets are priority 0-2 as well, so the window worker at 0..0 also took 2026
history at 0 (25k ranges in 40 groups, fetched live) while 1,739 ranges of the
2016 corpus window sat at voyager 2's leftover priorities (done when the window
was marked, planned again by the reset). With LEASE_CAPTURE_ONLY the lease, next
and the prefetcher's run-ahead take capture ranges only; the run-ahead now also
keeps to the lease bounds. Test: a group with history at 0 only isn't leased,
the history range after the window isn't handed out.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

REBUILD.md

@@ -544,6 +544,13 @@ releases, a third of them one poster's image dump (27.7 M rows, LOG.md
    (a live reply cut short; the spool doesn't check) is reported after
    the batch before it went out and the range asked for again from that
    chunk: the window stays (the first run lost it, and the open batch).
+   The lease bounds alone don't select a window: the history planner's
+   oldest buckets are priority 0–2 too, so the first run also took 2026
+   history at 0 (25k ranges in 40 groups, fetched live) while 1,739 of
+   the 2016 corpus ranges sat at voyager 2's leftover priorities (done
+   when the window was marked, planned again by the reset): hence
+   `LEASE_CAPTURE_ONLY` (the lease, next and the prefetcher's run-ahead
+   take capture ranges only) and the one-off repair of the priorities.
 
 6. **The corpus stays as it is.** Measured on 300 unfiltered chunks
    (30 M lines, LOG.md (102)): 43% of lines lack a "(k/N)" counter, and of