Here is a short new paper on how to reconcile the geometric approach to phi-feature agreement pursued in my 2014 monograph with earlier results supporting agreement as feature-sharing (Gazdar et al. 1985, Pollard & Sag 1994, Frampton & Gutmann 2000, 2006, Pesetsky & Torrego 2007, i.a.).
The paper is newish in the sense that it was written about a year ago, but it was part of a secret, surprise festschrift for David Pesetsky, which was presented to him at the workshop in honor of his 60th birthday.
For more details, please see my research page.