fix system, consecutive same role, and empty message parsing for anthropic

examples/foundational/20c-persistent-context-anthropic.py

@@ -94,11 +94,16 @@ async def load_conversation(function_name, tool_call_id, args, llm, context, res
         await result_callback({"success": False, "error": str(e)})
 
 
+# Test message munging ...
 messages = [
     {
         "role": "system",
         "content": "You are a helpful LLM in a WebRTC call. Your goal is to demonstrate your capabilities in a succinct way. Your output will be converted to audio so don't include special characters in your answers. Respond to what the user said in a creative and helpful way.",
     },
+    {"role": "user", "content": ""},
+    {"role": "assistant", "content": []},
+    {"role": "user", "content": "Tell me"},
+    {"role": "user", "content": "a joke"},
 ]
 tools = [
     {