builder

type Artifact struct{ From, To string }

type Builder interface {
	Name() string
	Dockerfile(port int, env map[string]string) (string, error)
}

type Plan struct {
	Base       string            // build/runtime base image
	CacheFiles []string          // manifest files to copy before Install (layer caching)
	Install    []string          // install commands
	Build      []string          // build commands (empty if none)
	Env        map[string]string // env available at build time (ENV in the build stage)

	// Multi-stage server: when RuntimeBase is set, the final image is RuntimeBase
	// with artifacts copied from the build stage (e.g. a compiled Go binary).
	RuntimeBase string
	Copy        []Artifact

	// Exactly one of these says how to serve:
	StaticDir string   // serve this directory of static files, or
	Start     []string // run this command (rendered as an exec-form CMD)

	Port int
}