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/src/broker-nats.ts

@@ -498,9 +498,9 @@ async function deliver(
   try {
     env = toEnvelope<unknown>(msg);
   } catch {
-    // Unparseable: acknowledge it. Redelivering a message no version of this code can read is
-    // an infinite loop, and the stream's dead-letter is for handlers that fail, not for bytes
-    // that were never an envelope.
+    // Unparseable: terminate it. Redelivering a message no version of this code can read is
+    // an infinite loop, and what the controller keeps of a message given up on (DEAD_LETTERS,
+    // novox/hq issue 330) is for handlers that fail, not for bytes that were never an envelope.
     msg.term();
     return;
   }
@@ -517,8 +517,11 @@ async function deliver(
     msg.ack();
   } catch {
     // Negative-acknowledge with a delay, so a handler failing on a transient cause gets another
-    // attempt, and one failing permanently exhausts max-deliver and dead-letters rather than
-    // spinning. The consumer's limits are the controller's; this only says "not done".
+    // attempt, and one failing permanently exhausts max-deliver rather than spinning: the consumer
+    // gives the event up, and the controller keeps it in DEAD_LETTERS until a person delivers it
+    // again or drops it (novox/hq issue 330). Delivered again, it arrives under
+    // `mesh.again.<consumer>.…`, and keyFromSubject reads the same key from it. The consumer's
+    // limits are the controller's; this only says "not done".
     msg.nak(5_000);
   }
 }