The Sandwich de Chantier is defined by its job rather than its filling: it is the big, cheap, filling sandwich built to be eaten on a worksite, and every choice in it follows from that brief. The name means the building-site sandwich, and the form is a long length of bread, often a full or half baguette, loaded heavily and plainly with whatever is substantial and inexpensive, usually ham, a hard cheese, a cured sausage, sometimes more than one at once, with butter and little else. It is not a sandwich about a single ingredient; it is a sandwich about being enough food.
The logic is entirely practical. It has to survive a morning in a bag, eat well cold, and hold together in one hand while the other is busy, so the build favors bread with a real crust that does not go soft, fillings that keep without refrigeration for a few hours, and a fill weight chosen for satisfaction rather than balance. The constraint is durability over refinement: no wet salad to soak the crumb, no soft component that collapses, no melted layer that only works hot, because none of that survives the conditions the sandwich is built for. Butter does double duty as a fat and a moisture barrier between a strong filling and the bread. Generosity is the point: a thin sandwich fails the brief no matter how good its parts, and the form is judged by whether it carries a working person to the next meal. It is best within a few hours of assembly, but it is built to tolerate not being.
Variations are a matter of what is on hand and what is cheap rather than codified swaps. A ham-and-hard-cheese version is the plainest; a cured-sausage one keeps best through a long morning; a double-filled one stacks meat and cheese together when the day is long and the work is heavy. Each holds the brief constant, big and durable and filling, and changes only the cheap substantial thing inside. The Sandwich de Chantier sits with the use-named builds the catalog groups under Regional Specialty Sandwiches. Its specific contribution is that it is defined by its use, a sandwich engineered to be plentiful, cheap, and still good after hours in a worker's bag.