How to build a linear LED driver that is dimmable?

You might want to try TA’s Commander driver:

Not in use in any light as far as I know, but it tested very well. It just tends to overheat in the mid-range amps (2-3 A). Your 1 A requirement sounds like a perfect fit. It has true linear regulation in 255 steps. It even works with most of the firmware around here if you do not need the DD mode or moon mode.