1. Cut rye bread into 3/4-inch cubes. Pour oil into a heavy zip-lock plastic bag or a plastic storage container with a lid. Add bread cubes, seal bag or container, and shake well, turning to coat bread evenly with oil. Pour into a 10- by 15-inch baking pan and bake in a 400° regular or convection oven until bread is crisp and lightly browned, 8 to 10 minutes (5 to 6 minutes in convection oven); shake pan to turn cubes halfway through baking. Let cool.
2. Meanwhile, rinse, core, and finely shred cabbage. Cut bacon crosswise into thin strips. In a 12-inch nonstick frying pan or 14-inch wok over medium-high heat, stir bacon until crisp and brown, 5 to 8 minutes. Using a slotted spoon, transfer bacon to paper towels to drain. Add onion to pan with bacon fat. Stir just until limp, about 3 minutes. Pour in 3 tablespoons vinegar and stir until liquid is reduced to a thick syrup, 1 minute longer.
3. Add cabbage to pan and sprinkle with salt and 1/2 teaspoon caraway seeds. Stir until cabbage is wilted but still crunchy, 3 to 5 minutes. Stir in remaining 3 tablespoons vinegar.
4. Spoon salad onto plates and top equally with rye croutons, bacon pieces, and remaining 1 teaspoon caraway seeds.