A voice companion has an uncomfortable product tension: users do not want to approve every sentence, but they also do not want the AI quietly deciding when to become a coach, critic, or adviser.
The tempting fix is a larger system prompt full of standing instructions. That can improve model behavior, but it is not a control system. Prompts are probabilistic, conversation history can pull behavior off course, and a response generated under an old instruction may arrive after the user has changed modes.
A better design gives the user a visible operating mode:
Listen: acknowledge and reflect without offering solutions.
Explore: ask questions and surface possibilities.
