A duplex Japanese dining shed in the middle of East Fourth Street? Next, how about a caviar pavilion with a rooftop pool?

The city for once acted swiftly in nixing a flagrant violation of outdoor dining regulations. The fiasco demonstrated the urgency to turn anything-goes rules into a rational, public-respecting framework worthy of the Big Apple. Thanks to the Open Restaurants program to give struggling eateries an alfresco lifeline, owners threw up every ramshackle structure short of a skyscraper to cram in as many bodies as possible. Many of them actually doubled the number of seats without costing owners an additional dime in rent.

New rules to tame the plywood beasts are expected by year’s end. But beyond the laughs provoked by the sight of a double-decker food tower on a leafy East Village street lurks a dangerous urban pathology.

“No rules enforced,” the neighborhood group LES Dwellers tweeted about the Izakaya NYC situation — but it might stand for City Hall’s overall abandonment of our streets to anarchy.

The chaos transcends gang-driven crime and harassment by “homeless” psychotics. It runs the gamut of unlicensed, untaxed sidewalk vendors who poach business from legitimate shops, and proliferating “pedestrian plazas” that are lolling grounds for fentanyl freaks.

Overbuilt street cafes aren’t in the same class, of course. But like the atrocities, they’re the toast of car-hating cranks who would give streets back to the “people” — as if all those autos were driven by lifeless robots.

Izakaya’s neighbors had enough this time. But they also tweeted, “It is going to be impossible to unravel this mess in a year.” Let’s hope a new mayor can prove them wrong.