qBittorrent had no network interface configured, so libtorrent listened
and announced on every interface of the shared pod network namespace -
including eth0 (the pod IP) and loopback. gluetun's kill switch drops
exactly those packets, so trackers answered with "skipping tracker
announce (unreachable)" or timed out, no peers were found and torrents
stalled at 0 bytes in stalledDL. Beyond the stall this is a leak: without
the binding qBittorrent also listens on the pod IP, i.e. reachable past
the tunnel.
The setting only exists in the persisted config file, which qBittorrent
creates itself on first start, so an init container seeds it before the
app comes up. The edit is idempotent and preserves existing user
settings: it replaces the keys if present, inserts them into the
[BitTorrent] section if missing, and creates file or section if needed.
The interface is configurable via qbittorrent.networkInterface (default
tun0); emptying it drops the init container.