Let L be a (spin, compact) Lagrangian in a holomorphic symplectic variety X. Given a square root K_L^(1/2) of the canonical line bundle of L, consider the dga RHom(K_L^1/2,K_L^1/2) in D(X) and the corresponding local-to-global Ext spectral sequence computing its cohomology. I will explain how mirror symmetry and results of Ivan Smith and Solomon–Verbitsky motivate the degeneration of the spectral sequence and prompt the question whether the dga is formal. I will sketch a proof of the degeneration using deformation quantisation and state the formality result. If time allows (which it won’t), I’ll mention various generalisations to pairs of Lagrangians and A_inf categories as well as some open questions.