fix: crash on None entry in tool_calls list during Anthropic conversion (#2209)

If a tool_calls list contains a None entry (from malformed API response,
compression artifact, or corrupt session replay), convert_messages_to_anthropic
crashes with AttributeError: 'NoneType' object has no attribute 'get'.

Skip None and non-dict entries in the tool_calls iteration. Found via
chaos/fuzz testing with mixed valid/invalid tool_call entries.

agent/anthropic_adapter.py

@@ -864,6 +864,8 @@ def convert_messages_to_anthropic(
                 else:
                     blocks.append({"type": "text", "text": str(content)})
             for tc in m.get("tool_calls", []):
+                if not tc or not isinstance(tc, dict):
+                    continue
                 fn = tc.get("function", {})
                 args = fn.get("arguments", "{}")
                 try: