wire it all together — a cli agent in 12 steps

Claude wrote a tool round-trip that drops the assistant's tool_use message before sending the next request. The script counts how many messages should be in the history after one tool call (it should be 3: user prompt, assistant tool_use, user tool_result). Right now it's 2. Add the missing append on line 14 so the count is exactly 3.

Expected output:

3