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>

config/coordinator.ts

@@ -33,11 +33,14 @@ export default {
   leaseTtlSeconds: env.get('LEASE_TTL_SECONDS', 15 * 60),
   /**
    * The ranges group leases hand out (REBUILD.md design 1), by priority: the tail is negative, the capture windows
-   * 0–2 (2016, 2021, 2025), the rest of the history above (its position in the group, or 4000+). Bounds so a
-   * deployment can run one window first (homelab 2026-10-26: 0..0, the 2016 window); unbounded by default.
+   * 0–2 (2016, 2021, 2025), the history by its position in the group (0 oldest … 1000 newest: its first buckets
+   * share 0–2 with the windows) or 4000+. Bounds so a deployment can run one window first, with
+   * LEASE_CAPTURE_ONLY so the history's 0 isn't taken along (homelab 2026-10-26: 0..0 and capture only, the 2016
+   * window; LOG.md (118)); unbounded and any range by default.
    */
   leasePriorityMin: env.get('LEASE_MIN_PRIORITY', -1_000_000),
   leasePriorityMax: env.get('LEASE_MAX_PRIORITY', 1_000_000),
+  leaseCaptureOnly: env.get('LEASE_CAPTURE_ONLY', false),
   /** NNTP connections the coordinator fetches headers with: at most (its share, nntpShares), and at least while sharing. */
   nntpConnections: env.get('NNTP_CONNECTIONS', 4),
   nntpMinConnections: env.get('NNTP_MIN_CONNECTIONS', 8),