Keep initial peer transfers, retry attempts, and chunk receivers structurally owned until they quiesce. Cancellation now stops opening new streams, flushes accepted file writes, and drains active work before ownership rollback can begin.
Leave operation admission owned by the running download task when liveness detects that every source disappeared, and emit the peers-gone notification only once.
Test Plan:
- just fmt (Rust and configured formatters completed; 39 pre-existing rumdl findings remain)
- just clippy
- just test
- git diff --cached --check
ddidderr
5bb4a8b611