Idle connections fetch capture ranges into the corpus

The spool only fetches what workers lease soon, in priority order, and the
tail never ends: after a reset the 1,400 capture ranges waited behind it
while 34 of 40 connections idled. Up to CORPUS_AHEAD (8) planned capture
ranges whose chunks aren't all stored are now targets after everything else,
fetched into the corpus only (no spool); a later lease reads them from disk.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

config/coordinator.ts

@@ -80,6 +80,12 @@ export default {
   /** Stored XOVER chunks of ranges marked `capture`, for the grouping sweeps (app/services/corpus.ts). Off when unset. */
   corpus: {
     dir: env.get('CORPUS_DIR'),
+    /**
+     * Capture ranges fetched into the corpus by connections the spool leaves idle, this many at a time: the
+     * spool only fetches what workers lease soon, and the tail comes first, so after a reset the capture
+     * ranges waited behind it for hours (1,400 marked, none stored, 34 of 40 connections idle; LOG.md 2026-10-12 (27)).
+     */
+    ahead: env.get('CORPUS_AHEAD', 8),
   },
   spool: {
     dir: env.get('SPOOL_DIR', app.tmpPath('spool')),