How do I stay a public servant instead of chasing my own advancement?

You hold your role rightly: as service to people you will never meet, their good set above your own climb. That is what public service is supposed to mean, and it is rarer than it should be. Plenty of people in your seat serve mainly themselves. You have chosen otherwise. The pull toward advancement never fully disappears. There is always a way to look good, to protect your position, to put your name first. Keeping the public's good above that is a daily choice, not a settled fact. What steadies you is remembering that the power was lent to you for them, not the other way around. Protect this by watching the small moments, the quiet chances to take credit or dodge blame. Serve the same whether it helps your career or not. That consistency is your integrity, and it is worth more than any promotion. You are a servant of people you will never meet. Keep governing like one.