  Firstly, bilinear Fourier Restriction estimates --which are well-known for
free waves-- are extended to adapted spaces of functions of bounded quadratic
variation, under quantitative assumptions on the phase functions. This has
applications to nonlinear dispersive equations, in particular in the presence
of resonances. Secondly, critical global well-posedness and scattering results
for massive Dirac-Klein-Gordon systems in dimension three are obtained, in
resonant as well as in non-resonant regimes. The results apply to small initial
data in scale-invariant Sobolev spaces exhibiting a small amount of angular
regularity.
