Cairo Native Interop?

Taking this as my basic example for lack of better explanation

local lgi = require("lgi")
local Gtk = lgi.require("Gtk", "3.0")
local cairo = lgi.cairo
local window = Gtk.Window {
	title = "Drawing Area",
	default_width = 600,
	default_height = 600,
	on_destroy = Gtk.main_quit
}

function window:on_draw(cr)
	--Here's the context `cr`
	--Lets assume this is passed by a controlling C process:
	local ptr = cr._native
	--Lets try to get an LGI context from the pointer:
	local ctx = cairo.Context(ptr) -- This will fail, because it expects a surface
end

local da = Gtk.DrawingArea {
	expand = true
}

window:add(da)
window:show_all()
Gtk:main()

Is there a proper way of retrieving the actual cairo.Context object being used with lgi here, or should a workaround be found?

No repository file or test is named; start with the Lua example and trace how lgi exposes cairo.Context and the _native pointer. Define what supported Cairo interop should look like, then verify the chosen behavior against the GTK drawing callback scenario.