PARIS — Beware that basket of limp crust put in front of you. Not all French bread is created equal. So sacred is the classic baguette that French law strictly codifies it, protects it and regulates it.

There are in fact few things more closely associated with France than the baguette, that long crusty stick that announces its nationality like no other bread.

So the mastering of that symbol of Frenchness by Mahmoud M’seddi, an immigrant’s son and this year’s winner of the Grand Prize for Best Parisian Baguette, is about more than great baking. At a moment when President Emmanuel Macron is taking a toughening line against immigration, Mr. M’seddi’s triumph challenges the very notion of what it means to be French.

Ask him whether there was any significance in the fact that his father arrived from Tunisia more than 30 years ago, and he will snort an indignant denial: “I’m French. This is my home.”