Layered configuration only stays useful if people can predict the result without mentally simulating the whole stack.

In envstack, left-to-right precedence gives each layer a clear role: base values come first, more specific overrides arrive later, and the final result follows the same order you read in the command line.

That sounds minor, but it removes a surprising amount of friction. When a production override wins because it appears later in the list, the behavior is visible in the invocation itself rather than hidden in special-case merge rules.

The goal is not novelty. The goal is a rule you can explain in one sentence and trust six months later.