I understand that hooks are available by modifying a recipe in the toolchain. The disadvantage of this approach is that someone who downloads my sketch or library must modify their toolchain, and this isn't trivial for a novice. Also the changes apply to all sketches, not just to my sketch.

My request is that the toolchain look in the sketch or library directory for custom hooks. That way I could rely on them being present without toolchain modifications. Specifically, I want to do something like git-describe-arduino.

Or perhaps I'm not understanding things (being a bit of an Arduino-novice myself!)