Rebuild: the live tail

coordinator:run plans the articles after each group's last range every
TAIL_EVERY_SECONDS (120): one LIST ACTIVE per name prefix gives every
group's newest article, and new articles become ranges at priority -1,
leased and prefetched before any history. A group gets a tail range once
it has TAIL_MIN_ARTICLES (100k, a chunk) new or its last planning is
TAIL_MAX_DELAY_MINUTES (15) ago, so quiet groups don't make a range every
round. History (planAll, hourly) is now only for groups not planned yet.
ranges:plan --tail plans one round.

Found on the way: with XFEATURE COMPRESS GZIP on, Eweka compresses LIST
ACTIVE's reply too ("215 NewsGroups Follow [COMPRESS=GZIP]"), and
listActive waited for a plain end that never came (groups:add --top too).
It reads the compressed reply now; the fake server in the test does both.

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

config/coordinator.ts

@@ -12,6 +12,20 @@ export default {
    * 2026-10-09).
    */
   chunkArticles: env.get('CHUNK_ARTICLES', 100_000),
+  /**
+   * The live tail (REBUILD.md, coordinator): new articles become ranges
+   * every `everySeconds` (one LIST ACTIVE per name prefix), leased and
+   * fetched before any history. A group gets a tail range once it has
+   * `minArticles` new (a chunk) or its oldest unplanned article waited
+   * `maxDelayMinutes`, so a quiet group doesn't make a range every round.
+   */
+  tail: {
+    everySeconds: env.get('TAIL_EVERY_SECONDS', 120),
+    minArticles: env.get('TAIL_MIN_ARTICLES', 100_000),
+    maxDelayMinutes: env.get('TAIL_MAX_DELAY_MINUTES', 15),
+    /** Before the history's 0 (oldest) … 1000 (newest). */
+    priority: -1,
+  },
   /** A leased range without a heartbeat for this long goes back to the queue. */
   leaseTtlSeconds: env.get('LEASE_TTL_SECONDS', 15 * 60),
   /** NNTP connections the coordinator fetches headers with. */