Yesterday (1 July) should have been a day to celebrate in Mexico as its newly revamped trade deal with the US and Canada - the US-Mexico-Canada Agreement (USMCA) - swung into effect. But instead of hosting a fiesta over the extension of a pact to export textiles and apparel duty-free to the world's biggest market, the Aztec nation is counting its losses amid tumbling shipments to its key northern neighbour.