Is the effect of a mending cantrip a continuous spell?

Suppose I have split a stone brick in two, hollowed it out, packed it full of contraband, and then sealed it shut with a Mending cantrip. How does the spell effect work? Is it a one-and-done, ending when the affected object is repaired, or does it continuously keeping the object’s pieces together?

Will Detect Magic pick up the brick?

Could the brick be opened by a Dispel Magic?

Would the effect cease inside an Antimagic Field? Will it resume once the brick is out of the field?