Say what becomes of an event a handler gives up on (hq issue 330)

The comments said a failing event dead-letters, which nothing did; the
controller now keeps it, and delivers it again under a subject this runtime
reads the same key from (ADR 0264).

node-tools/internal/bus/bus.go

@@ -839,7 +839,10 @@ func ConsumerOf(node, module string) string {
 }
 
 // NakDelay is how long an event a handler failed waits before it is offered again: a transient cause
-// gets another attempt, a permanent one exhausts the consumer's max-deliver rather than spinning.
+// gets another attempt, a permanent one exhausts the consumer's max-deliver rather than spinning. The
+// consumer then gives the event up, and the controller keeps it in DEAD_LETTERS until a person delivers
+// it again — under `mesh.again.<consumer>.…`, from which keyOf reads the same key — or drops it
+// (novox/hq issue 330).
 var NakDelay = 5 * time.Second
 
 // ConsumeAs reads a module's durable consumer and hands each event to deliver (novox/hq ADR 0198):