Release a message's hold when the response goes out, or when its listener failed

AGENTS.md

@@ -351,7 +351,11 @@ Grouped by what each one constrains.
   drain waits for. Counting every inbound request until `sendReturn()` answered it was rejected —
   an `onRequest` that deliberately answers nothing would then cost a full `shutdownTimeout` on every
   close — and a message no listener took is released at once, since nothing is going to answer it.
-  `teardown()` drops what is still held for the same reason it drops inbound segments. The release
+  A listener that threw or rejected before answering releases it the same way, for the same reason,
+  with `sessionError` carrying the failure. What ends the wait is the response reaching the wire, not
+  the call: a `sendResp()` the library refused leaves the message held, so `close()` still reports the
+  one the peer is owed. `teardown()` drops what is still held for the same reason it drops inbound
+  segments. The release
   is one turn late, so a listener that sends its receipt straight after the response is still
   holding when the drain looks; `sendDlr()` is the one send that goes out past the drain's refusal,
   and only while the message is still held — past that it is an ordinary send, because the drain it