feat: load explicit configuration references and remove implicit env overlays

examples/configuration/main.go

@@ -17,16 +17,18 @@ var examples embed.FS
 
 type ClientConfig struct {
 	Endpoint string        `json:"endpoint"`
-	Timeout  time.Duration `json:"timeout" envDefault:"3s"`
-	// This field is deliberately unavailable to configuration files.
-	Token string `json:"-" env:"DEMO_CLIENT_TOKEN,secret"`
+	Timeout  time.Duration `json:"timeout"`
+	// The file chooses a fixed value or an explicit environment reference.
+	Token string `json:"token"`
 }
 type Config struct {
 	Client   ClientConfig `json:"client"`
-	MaxItems int          `json:"maxItems" envDefault:"20"`
+	MaxItems int          `json:"maxItems"`
 	Allowed  []string     `json:"allowed"`
 }
 
+func Default() Config { return Config{Client: ClientConfig{Timeout: 3 * time.Second}, MaxItems: 20} }
+
 func (c Config) Validate() error {
 	if c.Client.Timeout <= 0 {
 		return config.Invalid("client.timeout", "must be positive")
@@ -48,7 +50,7 @@ func load(path string) (Config, error) {
 	if err != nil {
 		return Config{}, err
 	}
-	return config.LoadProject(path, Config{}, config.EnvOptions{Prefix: "DEMO_", Empty: "reject"}, loader)
+	return config.LoadProject(path, Default(), loader)
 }
 func run() error {
 	path := flag.String("config", "", "external configuration file")