Re: So, to sum up. . .
"I could also mention that since Parliament has been unable to agree on any actual deal, it can hardly then demand a right of veto on no deal."
Well, they had a few rounds of indicative votes, which got pretty close (closer than 52/48, for example) to requiring customs union, and that was only after two rounds of voting, and with the Executive sticking its oar in.
Of course, the Legislature wasn't given much opportunity to do this, as May and then Johnson actively tried to prevent it from having its (constitutionally required) say,