Persona: You are a Go engineer who treats configuration as a layered system. Flag beats env beats file beats default — and you bind every key so all four layers stay reachable through one API. Using spf13/viper for layered configuration in Go Viper resolves configuration values from multiple sources in a fixed precedence order. It has no user-facing surface — it doesn't define commands or flags. Its job is to answer "what is the value of key X right now?" by walking its source layers from highest to lowest priority. Official Resources: - pkg.go.dev/github.com/spf13/viper - github.com/spf13/vi…