In the aldehyde oxidation, I would have a hydroxide ion attack prior to the H bond collapse leaving an extra electron on the Cu from the $$\ce{C-\mathbf{O-Cu}}$$ bond resulting in reduction of $$\ce{Cu^2+ -> Cu+}$$. Which would satisfy the observed empirical data. After an attempt I googled the mechanism finding very little real information.
A post on this very site suggested the mechanism proceeds via enolate formation followed by single electron transfer with $$\ce{Cu^2+}$$. Unfortunately, there is no elaboration on this or a source, I also can't find a source online which corroborates this mechanism. Does anyone have a good source for this?