Rebuild: coordinator (planner, NNTP pool, spool, prefetcher, leases, rule sets), node API and the edge:node worker

- groups:add / ranges:plan / nodes:create / coordinator:run commands
- the node API: lease, the range's chunks as one framed stream from the
  spool, batches, heartbeat, finish, release (node guard, token per node)
- edge:node: needs COORDINATOR_URL and NODE_TOKEN only (placeholders for
  the rest), posts a batch every 10 chunks, gives its range back on SIGTERM
- releases are gathered per batch: 1.04 chunk rows per release at 10
  chunks per batch (1.35 when built per XOVER chunk)
- partitions are checked per batch instead of remembered

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

app/services/nntp_pool.ts

@@ -0,0 +1,80 @@
+import env from '#start/env'
+import logger from '@adonisjs/core/services/logger'
+import coordinatorConfig from '#config/coordinator'
+import { XoverClient } from '#lib/nntp/index'
+
+/**
+ * The coordinator's header connections (REBUILD.md, decision e: workers
+ * have no NNTP account). At most NNTP_CONNECTIONS, reused; a connection
+ * that failed is closed and replaced on the next use.
+ */
+class NntpPool {
+  private idle: XoverClient[] = []
+  private open = 0
+  private waiting: ((client: XoverClient) => void)[] = []
+
+  get size() {
+    return coordinatorConfig.nntpConnections
+  }
+
+  async use<T>(work: (client: XoverClient) => Promise<T>): Promise<T> {
+    const client = await this.acquire()
+    let broken = false
+    try {
+      return await work(client)
+    } catch (error) {
+      broken = true
+      throw error
+    } finally {
+      this.release(client, broken)
+    }
+  }
+
+  private async acquire(): Promise<XoverClient> {
+    const ready = this.idle.pop()
+    if (ready) return ready
+    if (this.open < this.size) {
+      this.open++
+      try {
+        return await XoverClient.connect({
+          host: env.get('NNTP_HOST')!,
+          port: env.get('NNTP_PORT', 563),
+          user: env.get('NNTP_USER'),
+          password: env.get('NNTP_PASSWORD'),
+          secure: env.get('NNTP_SECURE', true),
+          compress: true,
+          timeoutMs: coordinatorConfig.nntpTimeoutMs,
+        })
+      } catch (error) {
+        this.open--
+        throw error
+      }
+    }
+    return new Promise((resolve) => this.waiting.push(resolve))
+  }
+
+  private release(client: XoverClient, broken: boolean) {
+    if (broken) {
+      this.open--
+      try {
+        client.close()
+      } catch (error: any) {
+        logger.debug(`Closing a failed NNTP connection: ${error.message}`)
+      }
+      // Someone waiting gets a fresh connection.
+      const next = this.waiting.shift()
+      if (next) this.acquire().then(next, () => this.waiting.unshift(next))
+      return
+    }
+    const next = this.waiting.shift()
+    if (next) next(client)
+    else this.idle.push(client)
+  }
+
+  async close() {
+    for (const client of this.idle.splice(0)) client.close()
+    this.open = 0
+  }
+}
+
+export default new NntpPool()