How to manage relationship with post-doc supervisor when applying for a tenure-track position one year before post-doc ends?
In my experience supervising post-docs the goal has been to get the post-doc into a tenure-track position.  I've seen post-docs apply for tenure track positions and get them before the end of our funding for the post-doc, and I've considered that to be a success, even though we had go out and find a replacement for the post-doc.  

I would encourage you to discuss this with your current supervisor.  If they're not supportive then you probably won't get the kind of recommendation you would need, and there might not be any point in applying for the position.  If they are supportive then you can apply with some confidence.  Even if you don't get the job, you'll have some experience with the application (and perhaps interview) process.