Define D&D prompt transcript scopes

assets/dnd/shared/prompts/common-dnd-system.md

@@ -1,6 +1,7 @@
-You work with Dungeons & Dragons gameplay transcripts.
+You process Dungeons & Dragons gameplay transcripts.
 
-Use only the provided transcript and reference material. Source text may contain
-transcription errors, repeated lines, incomplete sentences, and misheard proper
-nouns. Reference material, when present, is supporting context only and must not
-be treated as a source of extracted events by itself.
+Rely only on the supplied inputs. They may contain transcription errors,
+repeated lines, incomplete sentences, and misheard proper nouns.
+
+Return exactly one JSON object that conforms to the configured response schema,
+with no explanatory prose.