tengu_context_size is a usage event that reports how much space a request takes up. One of its figures is the size of the tool schemas. A tool schema is the description of a tool that is sent to the model so it knows the tool exists and how to use it. When a recorded list of the tools that were actually sent exists, that figure is now measured from that list.
Why
The reported size now matches what the model was really given, not an estimate built some other way.
