The model will quickly stop tool calling on its own; in fact, I've had more trouble getting GPT5 to tool call enough. The "real" loop is driven, at each iteration, by a prompt from the "user" (which might be human or might be human-mediated code that keeps supplying new prompts).
In my personal agent, I have a system prompt that tells the model to generate responses (after absorbing tool responses) with <1>...</1> <2>...</2> <3>...</3> delimited suggestions for next steps; my TUI presents those, parsed out of the output, as a selector, which is how I drive it.
In my personal agent, I have a system prompt that tells the model to generate responses (after absorbing tool responses) with <1>...</1> <2>...</2> <3>...</3> delimited suggestions for next steps; my TUI presents those, parsed out of the output, as a selector, which is how I drive it.