Finish implementation of the scriptorium migration

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

@@ -118,9 +118,6 @@ func TestChunkReturnsSceneChunksFromStructuredOutput(t *testing.T) {
 	if req.SessionID != "session-123" || req.ProfileID != "profile-scenes" {
 		t.Fatalf("session/profile = %q/%q, want session-123/profile-scenes", req.SessionID, req.ProfileID)
 	}
-	if len(req.Messages) != 0 || req.ResponseSchemaName != "" || len(req.ResponseSchema) != 0 {
-		t.Fatalf("legacy prompt fields set: messages=%#v schema=%q/%s", req.Messages, req.ResponseSchemaName, req.ResponseSchema)
-	}
 	transcript, ok := req.Inputs["transcript"]
 	if !ok {
 		t.Fatalf("transcript input missing from %#v", req.Inputs)
@@ -493,8 +490,18 @@ func (client *fakeScenesLLMClient) CompleteStructured(ctx context.Context, req c
 }
 
 func cloneStructuredCompletionRequest(req contracts.StructuredCompletionRequest) contracts.StructuredCompletionRequest {
-	req.Messages = append([]contracts.LLMMessage(nil), req.Messages...)
-	req.ResponseSchema = append(json.RawMessage(nil), req.ResponseSchema...)
 	req.Inputs = req.Inputs.Clone()
+	req.Vars = cloneVars(req.Vars)
 	return req
 }
+
+func cloneVars(in map[string]any) map[string]any {
+	if len(in) == 0 {
+		return nil
+	}
+	out := make(map[string]any, len(in))
+	for key, value := range in {
+		out[key] = value
+	}
+	return out
+}