🐛(vercel-sdk) allow tool calls to have no arguments

Some tools might not need arguments because they rely only
on the run context, we can allow that.

src/backend/chat/ai_sdk_types.py

@@ -22,7 +22,7 @@ class ToolCall(BaseModel):
 
     toolCallId: str
     toolName: str
-    args: Dict[str, Any]
+    args: Optional[Dict[str, Any]] = None
 
 
 class ToolResult(BaseModel):
@@ -38,7 +38,7 @@ class ToolResult(BaseModel):
 
     toolCallId: str
     toolName: str
-    args: Dict[str, Any]
+    args: Optional[Dict[str, Any]] = None
     result: Any
 
 

src/backend/chat/clients/pydantic_ui_message_converter.py

@@ -119,7 +119,7 @@ def model_message_to_ui_message(model_message: ModelMessage) -> UIMessage:  # no
                             raise ValueError(
                                 f"Unsupported UserContent in UserPromptPart: {type(c)}"
                             )
-            elif isinstance(part, TextPart):
+            elif isinstance(part, TextPart) and part.content:
                 parts.append(TextUIPart(type="text", text=part.content))
             elif isinstance(part, ToolReturnPart):
                 pass
@@ -188,7 +188,9 @@ def model_message_to_ui_message(model_message: ModelMessage) -> UIMessage:  # no
                             state="call",
                             toolCallId=part.tool_call_id,
                             toolName=part.tool_name,
-                            args=json.loads(part.args) if isinstance(part.args, str) else part.args,
+                            args=json.loads(part.args)
+                            if isinstance(part.args, str)
+                            else part.args or {},
                         ),
                     )
                 )