Feat: extract message output to file (#11251)

### What problem does this PR solve?

Feat: extract message output to file

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

agent/canvas.py

@@ -408,6 +408,10 @@ class Canvas(Graph):
                     else:
                         yield decorate("message", {"content": cpn_obj.output("content")})
                         cite = re.search(r"\[ID:[ 0-9]+\]",  cpn_obj.output("content"))
+
+                    if isinstance(cpn_obj.output("attachment"), tuple):
+                        yield decorate("message", {"attachment": cpn_obj.output("attachment")})
+                        
                     yield decorate("message_end", {"reference": self.get_reference() if cite else None})
 
                     while partials: