Function send_done 

pub fn send_done(done_tx: &SyncSender<TaskReport>, report: TaskReport)

Hands a finished report off to the finalize thread over the bounded done channel. A full channel blocks the producer (backpressure — see DONE_QUEUE_CAPACITY). An Err means the finalize receiver is gone (the thread died) — the report can’t be persisted, but its task stays Queued and is recovered on restart, and the manager’s supervision aborts the dispatcher, so we only log.