refactor: Replace reflection-based Viper defaults with embedded template

Load the embedded config template as the Viper base so all keys are
registered upfront, enabling PMG_* env vars to work regardless of
whether a key exists in the user's config file.

config/config.template.yml

@@ -55,9 +55,7 @@ proxy_install_only: false
 #
 # The purl is the package identifier and the reason is the reason for trusting the package.
 # PURL specification: https://github.com/package-url/purl-spec
-trusted_packages:
-  - purl: pkg:npm/@safedep/pmg
-    reason: "PMG is a trusted package for PMG"
+trusted_packages: []
 
 # Sandbox configuration (EXPERIMENTAL)
 # When enabled, package managers run in sandbox environments with restricted

config/config_template_test.go

@@ -32,7 +32,7 @@ func TestTemplateParsesAsYAML(t *testing.T) {
 	assert.False(t, false, cfg.Paranoid, "expected Paranoid false")
 	assert.False(t, false, cfg.SkipEventLogging, "expected SkipEventLogging false")
 	assert.Equal(t, 7, cfg.EventLogRetentionDays, "expected EventLogRetentionDays 7")
-	assert.Len(t, cfg.TrustedPackages, 1)
+	assert.Empty(t, cfg.TrustedPackages)
 }
 
 func TestTemplateMatchesDefaults(t *testing.T) {
@@ -56,11 +56,7 @@ func TestTemplateMatchesDefaults(t *testing.T) {
 	assert.Equal(t, def.EventLogRetentionDays, parsed.EventLogRetentionDays, "event_log_retention_days mismatch")
 	assert.Equal(t, def.Verbosity, parsed.Verbosity, "verbosity mismatch")
 
-	assert.NotEmpty(t, parsed.TrustedPackages, "expected at least one trusted_packages entry")
-
-	first := parsed.TrustedPackages[0]
-	assert.NotEmpty(t, first.Purl, "first trusted package has empty purl")
-	assert.NotEmpty(t, first.Reason, "first trusted package has empty reason")
+	assert.Equal(t, def.TrustedPackages, parsed.TrustedPackages, "trusted_packages mismatch")
 
 	assert.Equal(t, def.DependencyCooldown.Enabled, parsed.DependencyCooldown.Enabled, "dependency_cooldown.enabled mismatch")
 	assert.Equal(t, def.DependencyCooldown.Days, parsed.DependencyCooldown.Days, "dependency_cooldown.days mismatch")

config/viper.go

@@ -3,7 +3,6 @@ package config
 import (
 	"fmt"
 	"os"
-	"reflect"
 	"strings"
 
 	"github.com/spf13/viper"
@@ -24,13 +23,14 @@ func loadViperConfig() error {
 	v.AutomaticEnv()
 	v.SetEnvKeyReplacer(strings.NewReplacer("-", "_"))
 
-	// Register all config struct fields as Viper defaults so that env vars work
-	// for any key Viper wouldn't otherwise know about — either because there is no
-	// config file, or because the key is absent from the file (e.g. commented out,
-	// or a new key added after the user last ran "pmg setup install").
-	registerViperDefaults(v, globalConfig.Config, "")
+	// Load the embedded template as the base so Viper knows all keys and their
+	// defaults. This is required for AutomaticEnv to resolve PMG_* env vars for
+	// keys that are absent from or newer than the user's config file.
+	if err := v.ReadConfig(strings.NewReader(templateConfig)); err != nil {
+		return fmt.Errorf("failed to load default config: %w", err)
+	}
 
-	// Merge the user config file on top if it exists.
+	// Merge user config on top if it exists.
 	if _, statErr := os.Stat(configPath); statErr == nil {
 		v.SetConfigFile(configPath)
 		if err := v.MergeInConfig(); err != nil {
@@ -38,8 +38,6 @@ func loadViperConfig() error {
 		}
 	}
 
-	// Unmarshal into a copy of the current defaults so that keys absent from
-	// both the env and the user config file retain their Go defaults.
 	merged := globalConfig.Config
 	if err := v.Unmarshal(&merged); err != nil {
 		return fmt.Errorf("failed to unmarshal config: %w", err)
@@ -48,42 +46,3 @@ func loadViperConfig() error {
 	globalConfig.Config = merged
 	return nil
 }
-
-// registerViperDefaults walks cfg (a struct) recursively via reflection and registers
-// each field as a Viper default using its mapstructure tag as the key. This is the
-// minimum required for AutomaticEnv to resolve env vars for those keys.
-func registerViperDefaults(v *viper.Viper, cfg any, prefix string) {
-	t := reflect.TypeOf(cfg)
-	val := reflect.ValueOf(cfg)
-
-	if t.Kind() == reflect.Pointer {
-		t = t.Elem()
-		val = val.Elem()
-	}
-
-	if t.Kind() != reflect.Struct {
-		return
-	}
-
-	for i := range t.NumField() {
-		field := t.Field(i)
-		fieldVal := val.Field(i)
-
-		tag := field.Tag.Get("mapstructure")
-		if tag == "" || tag == "-" {
-			continue
-		}
-
-		// Strip options like ",squash" or ",omitempty"
-		key := strings.SplitN(tag, ",", 2)[0]
-		if prefix != "" {
-			key = prefix + "." + key
-		}
-
-		if field.Type.Kind() == reflect.Struct {
-			registerViperDefaults(v, fieldVal.Interface(), key)
-		} else {
-			v.SetDefault(key, fieldVal.Interface())
-		}
-	}
-}