noldevin: a magnet stuck "downloading metadata" ran 11h despite a 15-min stall
timeout, got cleared from SoulSync but left active in qbit, then re-grabbed as a
duplicate. Two bugs:
1. Stall never fired on metaDL. StallTracker reset its clock on any `downloaded`
byte increase, but a metaDL torrent's byte counter still ticks up from DHT/peer
protocol overhead while making no real progress — so the clock reset forever.
Fix: the byte counter only counts once metadata is in (size>0). During the
metadata phase (size==0) the only thing that counts as progress is *obtaining*
metadata, so a magnet that can't even do that within the timeout is correctly
flagged stalled. size=None preserves the old byte-only behavior (back-compat).
2. Orphaned in qbit. The monitor's stall exit removed the torrent, but the `error`
exit and the 6h deadline exit only marked the download failed — leaving the
torrent active in qbit, untracked here, so SoulSync re-grabbed the same dead
torrent (qbit logs the duplicate-add). Fix: both terminal exits now run
_cleanup_torrent (shared with the stall path), which removes+deletes (abandon)
or pauses per the stall action — nothing is left orphaned.
Tests (10 new): metaDL byte-noise no longer resets the clock (stalls at timeout);
obtaining metadata resets it; real byte-progress still tracked after metadata;
_cleanup_torrent removes+delete_files on abandon / pauses on pause / no-ops on
empty hash or no adapter / swallows a client error. 151 torrent tests green.
