Close NNTP connections left idle for NNTP_IDLE_CLOSE_SECONDS

Eweka drops quiet connections, so the next command on one failed
("Spot inspection failed: NNTP connection closed"), and idle connections
held account slots that downloads could use. The coordinator pool now
closes free connections (and the plain one) on its sync once idle for
60 s; dry prober lanes, the spotter between rounds and the spot inspector
with nothing to inspect close theirs too, reconnecting when work comes.

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

app/services/nntp_pool.ts

@@ -12,7 +12,8 @@ const SHARE_MARGIN = 2
  * have no NNTP account). At most NNTP_CONNECTIONS, reused; a connection
  * that failed, or is older than NNTP_CONNECTION_MAX_MINUTES, is closed and
  * replaced on the next use. Sharing the account (share()), at most its
- * share: over it, connections close as they come free.
+ * share: over it, connections close as they come free. One left free for
+ * NNTP_IDLE_CLOSE_SECONDS is closed on the next sync.
  */
 class NntpPool {
   private idle: XoverClient[] = []
@@ -22,6 +23,8 @@ class NntpPool {
   private openedAt = new Map<XoverClient, number>()
   /** When a connection gets closed once free: its max age ±25%, so they don't all reconnect at once. */
   private retireAt = new Map<XoverClient, number>()
+  /** When an idle connection came free. */
+  private idleSince = new Map<XoverClient, number>()
   private limit = coordinatorConfig.nntpConnections
   /** Since the last sync: the most connections in use at once, and whether work waited for one (starved()). */
   private peak = 0
@@ -50,6 +53,7 @@ class NntpPool {
     this.limit = granted
     // Over the share: the idle ones close now, the busy ones once free (release()).
     while (this.open > this.limit && this.idle.length > 0) this.retire(this.idle.pop()!)
+    this.closeIdle()
     // Under it with work waiting: connections for it.
     while (this.waiting.length > 0 && this.open < this.limit) {
       const next = this.waiting.shift()!
@@ -93,9 +97,28 @@ class NntpPool {
     }
   }
 
+  /** Closes the connections free for nntpIdleCloseMs, the plain one too. */
+  private closeIdle() {
+    const idleMs = coordinatorConfig.nntpIdleCloseMs
+    if (idleMs <= 0) return
+    const before = Date.now() - idleMs
+    for (const client of this.idle.filter((c) => (this.idleSince.get(c) ?? Infinity) <= before)) {
+      this.idle.splice(this.idle.indexOf(client), 1)
+      this.retire(client)
+    }
+    if (this.plain && this.plainPending === 0 && this.plainUsedAt <= before) {
+      void this.plain.then((c) => c.close()).catch(() => {})
+      this.plain = null
+    }
+  }
+
   private async acquire(): Promise<XoverClient> {
+    // The one used last: the others stay free long enough to close.
     const ready = this.idle.pop()
-    if (ready) return ready
+    if (ready) {
+      this.idleSince.delete(ready)
+      return ready
+    }
     if (this.open < this.size) {
       this.open++
       try {
@@ -134,13 +157,17 @@ class NntpPool {
     }
     const next = this.waiting.shift()
     if (next) next(client)
-    else this.idle.push(client)
+    else {
+      this.idle.push(client)
+      this.idleSince.set(client, Date.now())
+    }
   }
 
   private retire(client: XoverClient) {
     this.open--
     this.openedAt.delete(client)
     this.retireAt.delete(client)
+    this.idleSince.delete(client)
     try {
       client.close()
     } catch (error: any) {
@@ -151,6 +178,9 @@ class NntpPool {
   /** Closes every connection, also those in use: their commands fail. */
   private plain: Promise<XoverClient> | null = null
   private plainQueue: Promise<unknown> = Promise.resolve()
+  /** Commands queued or running on the plain connection, and when the last one ended. */
+  private plainPending = 0
+  private plainUsedAt = 0
 
   /**
    * One connection without XFEATURE COMPRESS GZIP, opened when first needed,
@@ -158,6 +188,7 @@ class NntpPool {
    * cuts short (Leases.corrupt). Its replies are deflated here.
    */
   async usePlain<T>(work: (client: XoverClient) => Promise<T>): Promise<T> {
+    this.plainPending++
     const run = this.plainQueue.then(async () => {
       this.plain ??= XoverClient.connect({
         host: env.get('NNTP_HOST')!,
@@ -177,7 +208,10 @@ class NntpPool {
         throw error
       }
     })
-    this.plainQueue = run.catch(() => {})
+    this.plainQueue = run.catch(() => {}).finally(() => {
+      this.plainPending--
+      this.plainUsedAt = Date.now()
+    })
     return run
   }
 
@@ -188,6 +222,7 @@ class NntpPool {
     this.busy.clear()
     this.openedAt.clear()
     this.retireAt.clear()
+    this.idleSince.clear()
     this.open = 0
   }
 }