Complete archive listings by walking RAR headers, at low priority

Inspection lists only the entries whose headers are in the first segment
of a first volume. A walk hops from header to header, fetching one segment
per entry and volume, in its own queue (one job per collection worker) on
NNTP connections inspection isn't waiting for. content:walk-archives queues
releases inspected earlier (CONCEPT D40).

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

app/services/NntpService.ts

@@ -7,6 +7,8 @@ class NntpService {
   private allConnections: Set<any>;
   private idleConnections: any[];
   private waiters: ((conn: any) => void)[];
+  /** Background work (archive walks): served only when no one else waits. */
+  private lowWaiters: ((conn: any) => void)[] = [];
   private createdCount: number;
 
   constructor(poolSize = 10) {
@@ -34,7 +36,8 @@ class NntpService {
     return conn;
   }
 
-  public async acquire() {
+  /** A connection from the pool; with `low`, after every waiting normal caller. */
+  public async acquire(low = false) {
     if (this.idleConnections.length > 0) {
       return this.idleConnections.pop();
     }
@@ -45,7 +48,7 @@ class NntpService {
       return this._createConnection();
     }
 
-    return new Promise(resolve => this.waiters.push(resolve));
+    return new Promise(resolve => (low ? this.lowWaiters : this.waiters).push(resolve));
   }
 
   /**
@@ -58,7 +61,7 @@ class NntpService {
       this.discard(conn);
       return;
     }
-    const resolve = this.waiters.shift();
+    const resolve = this.nextWaiter();
     if (resolve) {
       resolve(conn);
     } else {
@@ -73,13 +76,17 @@ class NntpService {
     this._destroy(conn);
 
     // Someone is waiting for a slot: open a fresh connection for them.
-    const resolve = this.waiters.shift();
+    const resolve = this.nextWaiter();
     if (resolve) {
       this.createdCount++;
       this._createConnection().then(resolve, () => this.waiters.unshift(resolve));
     }
   }
 
+  private nextWaiter() {
+    return this.waiters.shift() ?? this.lowWaiters.shift();
+  }
+
   private _destroy(conn: any) {
     try {
       conn.sock?.destroy();
@@ -126,6 +133,7 @@ class NntpService {
     this.allConnections.clear();
     this.idleConnections.length = 0;
     this.waiters.length = 0;
+    this.lowWaiters.length = 0;
     this.createdCount = 0;
   }
 }