Code is only half the story. It needs somewhere to run, and that place decides whether the same program works perfectly or fails completely. Your codebase says what should happen; the runtime is where it happens. It might be Node.js, Python, a browser, or a cloud function, and it includes the language version, installed packages, memory, and permissions the code depends on.
A kitchen makes this concrete. A recipe on paper isn’t dinner. Dinner happens when the recipe meets the oven, pans, ingredients, and timing. The same recipe can fail in another kitchen if the oven is different or an ingredient is missing.
Why you care
This is why something works on one machine and fails elsewhere: the recipe didn’t change, the kitchen did. Maybe the production server runs a different Node version, maybe the agent assumed a file path that only exists on your laptop. A container packages the kitchen so the code gets the same oven everywhere. Agents write code and then run it, so a good agent needs to know where the code will run, what’s installed, and what permissions exist. That answer decides whether the work is simple, broken, or impossible without setup.