lexicon: the frame around a slot value, and the call-off words (V-560)

Two closed sets the turn-role classifier reads. slot_value_frame is what can
stand around a bare value without making the utterance a request — strip it
and the numbers and whatever is left is the utterance's own content.
dialogue_cancel is how he calls off a request she is still assembling, which
is not what task_drop_words means.

internal/lexicon/lexicon.go

@@ -124,6 +124,16 @@ func TaskDoneWords() []string { return words("task_done_words") }
 // TaskDropWords — see TaskDoneWords.
 func TaskDropWords() []string { return words("task_drop_words") }
 
+// SlotValueFrame returns the words that can surround a bare slot value without
+// making the utterance a request of its own. A caller strips these (along with
+// the numbers and the other closed time sets) to see whether an utterance
+// carries any content beside the value it was asked for. See the set's note.
+func SlotValueFrame() []string { return words("slot_value_frame") }
+
+// DialogueCancel returns the ways he calls off the request Maven is assembling.
+// Distinct from TaskDropWords, which abandons an item that already exists.
+func DialogueCancel() []string { return words("dialogue_cancel") }
+
 // IsFillerParticle reports whether a word can never be the subject of a
 // request: a particle, a politeness word, or the first-person object. See the
 // set's own note for why this is not a stopword list.