address PR comments

Author: nikhilc-microsoft

libraries/microsoft-agents-a365-observability-core/microsoft_agents_a365/observability/core/message_utils.py

@@ -194,7 +194,8 @@ def serialize_messages(
         )
     except Exception:
         logger.warning("Failed to serialize messages; using fallback.", exc_info=True)
-        count = len(wrapper.messages)
+        messages = getattr(wrapper, "messages", [])
+        count = len(messages) if isinstance(messages, list) else 0
         noun = "message" if count == 1 else "messages"
         fallback = {
             "version": A365_MESSAGE_SCHEMA_VERSION,

libraries/microsoft-agents-a365-observability-core/microsoft_agents_a365/observability/core/models/messages.py

@@ -91,7 +91,7 @@ class ReasoningPart:
 class BlobPart:
     """Inline binary data (base64-encoded)."""
 
-    modality: str
+    modality: Modality | str
     content: str
     mime_type: str | None = None
     type: str = field(default="blob", init=False)
@@ -101,7 +101,7 @@ class BlobPart:
 class FilePart:
     """Reference to a pre-uploaded file."""
 
-    modality: str
+    modality: Modality | str
     file_id: str
     mime_type: str | None = None
     type: str = field(default="file", init=False)
@@ -111,7 +111,7 @@ class FilePart:
 class UriPart:
     """External URI reference."""
 
-    modality: str
+    modality: Modality | str
     uri: str
     mime_type: str | None = None
     type: str = field(default="uri", init=False)