El web empuja SubtitleFetchRequest por el sync (URL del proxy, ya
charset-fixed a WebVTT); el daemon lo descarga y lo escribe como sidecar
<base>.<lang>.vtt junto al medio (contención en scan paths con
EvalSymlinks, cap 10 MiB) y reporta done/failed en el siguiente sync
para que el web marque el job. Config nueva library.subtitles
(auto_fetch + languages) para el auto-fetch en scan, off por defecto.
The torrent reader used a static 5 MiB readahead — about 1.9s of a 20 Mbps 4K
stream — so streaming a torrent while it downloaded outran the download and
stalled. anacrolix's reader already prioritises the pieces in the readahead
window ahead of the playhead (and re-prioritises on seek); the window was just
too small. dynamicReadahead sizes it to ~30s of video (clamped 8-96 MiB, 24 MiB
default when bitrate is unknown). The torrent provider probes the bitrate
asynchronously so stream start never blocks on ffprobe; readers created after
the probe resolves pick up the accurate size. Real 4K (20.7 Mbps) -> 73 MiB.
