diff --git a/internal/domain/domain.go b/internal/domain/domain.go
index 70daa42..a973166 100644
--- a/internal/domain/domain.go
+++ b/internal/domain/domain.go
@@ -230,6 +230,9 @@ const (
 	// first checked against the file's header, which a hostile or damaged file can lie
 	// about (ADR-035 review).
 	UploadErrTooLong UploadErrorKind = "audio_too_long"
+	// UploadErrBusy: too many recordings were already waiting, so this one was not
+	// queued. The user's to retry later (ADR-035 review).
+	UploadErrBusy UploadErrorKind = "queue_full"
 	// UploadErrIncomplete: the audio, once converted, ends far earlier than the file
 	// claimed: a truncated recording that would otherwise give a partial transcript with
 	// no warning.