Function is_streaming_virtual_field 

pub fn is_streaming_virtual_field(field: &str) -> bool

Returns true when field is a streaming-virtual field name, including deep-nested paths that start with a known streaming-virtual root.

Examples that return true:

• "tool_calls" (exact root)
• "tool_calls[0].function.name" (deep path)
• "tool_calls[0].id" (deep path)