Restore public API reference documentation

secret.go

@@ -18,6 +18,7 @@ type Secret struct {
 }
 
 // SecretEnv constructs an unresolved environment-backed secret reference.
+// Invalid names are reported if the reference survives a configuration load.
 func SecretEnv(name string) Secret { return Secret{name: name, specified: true} }
 
 // EnvName returns the public environment-variable name.