feat: add IsSet, AllKeys, AllSettings; fix env precedence for file-only keys

- collapse() now applies env vars for keys present in fileConfig, not
  just defaultConfig. Previously, env vars couldn't override file values
  unless a default was also set for that key.
- SetDefault no longer pollutes overrideConfig; it correctly resolves
  the value by checking override > env > file > default.
- Remove unused explicitDefaults field and UseExplicitDefaults method.
- Add IsSet, AllKeys, AllSettings methods + package-level wrappers.
- Add missing package-level wrappers: Get, SetBool, SetString,
  SetConfigDir, WithEnvPrefix.
- Add tests for all new methods and the env-over-file-without-default
  fix.

default.go

@@ -67,3 +67,35 @@ func GetStringMap(key string) map[string]any {
 func GetStringSlice(key string) []string {
 	return defaultConfigManager.GetStringSlice(key)
 }
+
+func Get(key string) any {
+	return defaultConfigManager.Get(key)
+}
+
+func SetBool(key string, value bool) {
+	defaultConfigManager.SetBool(key, value)
+}
+
+func SetString(key string, value string) {
+	defaultConfigManager.SetString(key, value)
+}
+
+func SetConfigDir(path string) {
+	defaultConfigManager.SetConfigDir(path)
+}
+
+func WithEnvPrefix(prefix string) *ConfigManager {
+	return defaultConfigManager.WithEnvPrefix(prefix)
+}
+
+func IsSet(key string) bool {
+	return defaultConfigManager.IsSet(key)
+}
+
+func AllKeys() []string {
+	return defaultConfigManager.AllKeys()
+}
+
+func AllSettings() map[string]any {
+	return defaultConfigManager.AllSettings()
+}

jety.go

@@ -28,17 +28,16 @@ type (
 	}
 
 	ConfigManager struct {
-		configName       string
-		configPath       string
-		configFileUsed   string
-		configType       configType
-		overrideConfig   map[string]ConfigMap
-		fileConfig       map[string]ConfigMap
-		defaultConfig    map[string]ConfigMap
-		envConfig        map[string]ConfigMap
-		combinedConfig   map[string]ConfigMap
-		mutex            sync.RWMutex
-		explicitDefaults bool
+		configName     string
+		configPath     string
+		configFileUsed string
+		configType     configType
+		overrideConfig map[string]ConfigMap
+		fileConfig     map[string]ConfigMap
+		defaultConfig  map[string]ConfigMap
+		envConfig      map[string]ConfigMap
+		combinedConfig map[string]ConfigMap
+		mutex          sync.RWMutex
 	}
 )
 
@@ -90,10 +89,48 @@ func (c *ConfigManager) ConfigFileUsed() string {
 	return c.configFileUsed
 }
 
-func (c *ConfigManager) UseExplicitDefaults(enable bool) {
-	c.mutex.Lock()
-	defer c.mutex.Unlock()
-	c.explicitDefaults = enable
+// IsSet checks whether a key has been set in any configuration source.
+func (c *ConfigManager) IsSet(key string) bool {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+	lower := strings.ToLower(key)
+	if _, ok := c.combinedConfig[lower]; ok {
+		return true
+	}
+	_, ok := c.envConfig[lower]
+	return ok
+}
+
+// AllKeys returns all keys from all configuration sources, deduplicated.
+func (c *ConfigManager) AllKeys() []string {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+	seen := make(map[string]struct{})
+	var keys []string
+	for k := range c.combinedConfig {
+		if _, ok := seen[k]; !ok {
+			seen[k] = struct{}{}
+			keys = append(keys, k)
+		}
+	}
+	for k := range c.envConfig {
+		if _, ok := seen[k]; !ok {
+			seen[k] = struct{}{}
+			keys = append(keys, k)
+		}
+	}
+	return keys
+}
+
+// AllSettings returns all settings as a flat map of key to value.
+func (c *ConfigManager) AllSettings() map[string]any {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+	result := make(map[string]any, len(c.combinedConfig))
+	for k, v := range c.combinedConfig {
+		result[k] = v.Value
+	}
+	return result
 }
 
 func (c *ConfigManager) collapse() {
@@ -107,8 +144,10 @@ func (c *ConfigManager) collapse() {
 	for k, v := range c.fileConfig {
 		ccm[k] = v
 	}
-	for k := range c.defaultConfig {
-		if v, ok := c.envConfig[k]; ok {
+	for k, v := range c.envConfig {
+		if _, inDefaults := c.defaultConfig[k]; inDefaults {
+			ccm[k] = v
+		} else if _, inFile := c.fileConfig[k]; inFile {
 			ccm[k] = v
 		}
 	}

jety_test.go

@@ -760,17 +760,6 @@ func TestPackageLevelFunctions(t *testing.T) {
 	}
 }
 
-func TestUseExplicitDefaults(t *testing.T) {
-	cm := NewConfigManager()
-	cm.UseExplicitDefaults(true)
-
-	// Just verify it doesn't panic and the field is set
-	cm.SetDefault("key", "value")
-	if got := cm.GetString("key"); got != "value" {
-		t.Errorf("GetString(key) = %q, want %q", got, "value")
-	}
-}
-
 func TestSetString(t *testing.T) {
 	cm := NewConfigManager()
 	cm.SetString("name", "test")
@@ -1397,3 +1386,83 @@ func TestPrecedenceChain(t *testing.T) {
 		t.Errorf("extra: got %q, want defaultextra (default)", got)
 	}
 }
+
+func TestIsSet(t *testing.T) {
+	cm := NewConfigManager()
+	cm.Set("exists", "yes")
+
+	if !cm.IsSet("exists") {
+		t.Error("IsSet(exists) = false, want true")
+	}
+	if cm.IsSet("nope") {
+		t.Error("IsSet(nope) = true, want false")
+	}
+}
+
+func TestAllKeys(t *testing.T) {
+	cm := NewConfigManager()
+	cm.SetDefault("a", 1)
+	cm.Set("b", 2)
+
+	keys := cm.AllKeys()
+	found := make(map[string]bool)
+	for _, k := range keys {
+		found[k] = true
+	}
+	if !found["a"] || !found["b"] {
+		t.Errorf("AllKeys() = %v, want to contain a and b", keys)
+	}
+}
+
+func TestAllSettings(t *testing.T) {
+	cm := NewConfigManager()
+	cm.Set("port", 8080)
+	cm.Set("host", "localhost")
+
+	settings := cm.AllSettings()
+	if settings["port"] != 8080 || settings["host"] != "localhost" {
+		t.Errorf("AllSettings() = %v", settings)
+	}
+}
+
+func TestEnvOverridesFileWithoutDefault(t *testing.T) {
+	// Bug fix: env should override file even when no default is set for that key
+	os.Setenv("HOST", "envhost")
+	defer os.Unsetenv("HOST")
+
+	dir := t.TempDir()
+	configFile := filepath.Join(dir, "config.yaml")
+	if err := os.WriteFile(configFile, []byte("host: filehost"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	cm := NewConfigManager()
+	cm.SetConfigFile(configFile)
+	if err := cm.SetConfigType("yaml"); err != nil {
+		t.Fatal(err)
+	}
+	if err := cm.ReadInConfig(); err != nil {
+		t.Fatal(err)
+	}
+
+	// No SetDefault("host", ...) was called — env should still win
+	if got := cm.GetString("host"); got != "envhost" {
+		t.Errorf("GetString(host) = %q, want envhost (env overrides file even without default)", got)
+	}
+}
+
+func TestPackageLevelIsSet(t *testing.T) {
+	defaultConfigManager = NewConfigManager()
+	Set("x", 1)
+	if !IsSet("x") {
+		t.Error("IsSet(x) = false")
+	}
+}
+
+func TestPackageLevelGet(t *testing.T) {
+	defaultConfigManager = NewConfigManager()
+	Set("key", "val")
+	if Get("key") != "val" {
+		t.Error("Get(key) failed")
+	}
+}

setters.go

@@ -33,14 +33,14 @@ func (c *ConfigManager) SetDefault(key string, value any) {
 	defer c.mutex.Unlock()
 	lower := strings.ToLower(key)
 	c.defaultConfig[lower] = ConfigMap{Key: key, Value: value}
-	if _, ok := c.overrideConfig[lower]; !ok {
-		if envVal, ok := c.envConfig[lower]; ok {
-			c.overrideConfig[lower] = ConfigMap{Key: key, Value: envVal.Value}
-			c.combinedConfig[lower] = ConfigMap{Key: key, Value: envVal.Value}
-		} else {
-			c.combinedConfig[lower] = ConfigMap{Key: key, Value: value}
-		}
+	// Update combinedConfig respecting precedence: override > env > file > default
+	if v, ok := c.overrideConfig[lower]; ok {
+		c.combinedConfig[lower] = v
+	} else if v, ok := c.envConfig[lower]; ok {
+		c.combinedConfig[lower] = ConfigMap{Key: key, Value: v.Value}
+	} else if v, ok := c.fileConfig[lower]; ok {
+		c.combinedConfig[lower] = v
 	} else {
-		c.combinedConfig[lower] = c.overrideConfig[lower]
+		c.combinedConfig[lower] = ConfigMap{Key: key, Value: value}
 	}
 }