Companion
Properties
Keep-alives go out roughly every 75 s of ticks, like write_keepalive's cadence.
Pieces a peer may contribute to that fail their hash before it is banned.
Max outstanding inbound requests a single peer may have pending against us before it is treated as flooding and disconnected (libtorrent's in-request-queue cap).
Hard ceiling on the byte length of an inbound request. libtorrent rejects requests larger than a single block; we bound by 128 KiB defensively.
min_request_queue: the dynamic queue never drops below this (except snub/end-game).
PEX gossip cadence: libtorrent's ut_pex_plugin ticks once a minute (60 s min).
Frame overhead of a piece message (4 length + 1 id + 8 piece/begin).
Slow start ends when a tick grows payload by less than this (upstream's 5000-byte slack).
How long an outgoing µTP SYN may wait before falling back to TCP.