qbt: create timer to flush WAL

services/qbittorrent.nix

@@ -164,6 +164,35 @@ in
     _: path: "d ${path} 0770 ${config.services.qbittorrent.user} ${service_configs.media_group} -"
   ) service_configs.torrent.categories;
 
+  # Periodically checkpoint qBittorrent's SQLite WAL (Write-Ahead Log).
+  # qBittorrent holds a read transaction open for its entire lifetime,
+  # preventing SQLite's auto-checkpoint from running. The WAL grows
+  # unbounded (observed: 405 MB) and must be replayed on next startup,
+  # causing 10+ minute "internal preparations" hangs.
+  # A second sqlite3 connection can checkpoint concurrently and safely.
+  # See: https://github.com/qbittorrent/qBittorrent/issues/20433
+  systemd.services.qbittorrent-wal-checkpoint = {
+    description = "Checkpoint qBittorrent SQLite WAL";
+    after = [ "qbittorrent.service" ];
+    requires = [ "qbittorrent.service" ];
+    serviceConfig = {
+      Type = "oneshot";
+      ExecStart = "${pkgs.sqlite}/bin/sqlite3 ${config.services.qbittorrent.profileDir}/qBittorrent/data/torrents.db 'PRAGMA wal_checkpoint(TRUNCATE);'";
+      User = config.services.qbittorrent.user;
+      Group = config.services.qbittorrent.group;
+    };
+  };
+
+  systemd.timers.qbittorrent-wal-checkpoint = {
+    description = "Periodically checkpoint qBittorrent SQLite WAL";
+    wantedBy = [ "timers.target" ];
+    timerConfig = {
+      OnUnitActiveSec = "4h";
+      OnBootSec = "30min";
+      RandomizedDelaySec = "10min";
+    };
+  };
+
   users.users.${config.services.qbittorrent.user}.extraGroups = [
     service_configs.media_group
   ];