NNTP shares: the account's connections shared by priority

The coordinator (38) and the prober (8) had a fixed split; with history
paused the coordinator's stood idle while the prober's were its limit.
nntp_shares: each process syncs every 15 s (priority, minimum, what it could
use, what it has open) and gets what it may open: minimums first, then by
priority what each wants, growing only into connections the others closed
or gave up. The pool's size and the prober's lanes follow the grant; the
coordinator doubles its want while work waits for a connection, else asks
for its peak in use and a margin; the prober wants its maximum unless the
queue is dry. Claims scale with the lanes.

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

app/services/prefetcher.ts

@@ -131,6 +131,8 @@ export class Prefetcher {
         .catch((error) => logger.warn(`Prefetching: ${error.message}`))
         .finally(() => this.running--)
     }
+    // Work left with every loop running: the pool's share could be bigger.
+    if (!this.stopped && this.running >= this.loops && this.peek()) NntpPool.starved()
   }
 
   stop() {
@@ -145,6 +147,9 @@ export class Prefetcher {
   /** One connection's loop: chunks until there is nothing left to fetch. */
   private async work() {
     while (!this.stopped) {
+      // The pool's share got smaller: fewer loops (waiting on the pool, they'd count as work short of a connection).
+      // Two leaving at once is one too many for a tick (TICK_MS), whose loop comes back.
+      if (this.running > this.loops) return
       const next = this.take()
       if (!next) return
       const { target, span } = next