Document D&D prompt conventions and verification

internal/modules/dnd/chunk/scenes/prompt_assets_test.go

@@ -25,9 +25,6 @@ func TestPromptAssetsPrepareTranscriptWithInstructionOrdering(t *testing.T) {
 	if prepared.OutputContract.SchemaPath != "dnd_scenes_llm.v1.json" {
 		t.Fatalf("scene output schema path = %q, want private LLM schema", prepared.OutputContract.SchemaPath)
 	}
-	if len(prepared.Messages) < 4 {
-		t.Fatalf("prepared messages = %#v, want system, references, instructions, and transcript", prepared.Messages)
-	}
 	if prepared.Messages[0].Role != "system" || prepared.Messages[1].Role != "user" {
 		t.Fatalf("initial prompt roles = %#v, want system followed by campaign references", prepared.Messages[:2])
 	}