fix!: SetEnvPrefix now re-reads env vars with prefix stripping

SetEnvPrefix was broken: it set the prefix string but never re-read
environment variables. This meant collapse() and SetDefault() couldn't
match prefixed env vars to their unprefixed config keys, so defaults
always won over env vars.

The fix makes SetEnvPrefix behave identically to WithEnvPrefix: it
re-reads os.Environ(), strips the prefix from matching keys, and
stores the stripped keys in envConfig. The envPrefix field is removed
entirely since keys are always pre-stripped.

BREAKING CHANGE: SetEnvPrefix now filters env vars to only those
matching the prefix (previously all env vars were accessible).
This matches the documented and expected behavior.

getters.go

@@ -12,7 +12,7 @@ func (c *ConfigManager) Get(key string) any {
 	defer c.mutex.RUnlock()
 	v, ok := c.combinedConfig[strings.ToLower(key)]
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
+		v, ok = c.envConfig[strings.ToLower(key)]
 		if !ok {
 			return nil
 		}
@@ -25,7 +25,7 @@ func (c *ConfigManager) GetBool(key string) bool {
 	defer c.mutex.RUnlock()
 	v, ok := c.combinedConfig[strings.ToLower(key)]
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
+		v, ok = c.envConfig[strings.ToLower(key)]
 		if !ok {
 			return false
 		}
@@ -56,7 +56,7 @@ func (c *ConfigManager) GetDuration(key string) time.Duration {
 	defer c.mutex.RUnlock()
 	v, ok := c.combinedConfig[strings.ToLower(key)]
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
+		v, ok = c.envConfig[strings.ToLower(key)]
 		if !ok {
 			return 0
 		}
@@ -91,7 +91,7 @@ func (c *ConfigManager) GetString(key string) string {
 	defer c.mutex.RUnlock()
 	v, ok := c.combinedConfig[strings.ToLower(key)]
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
+		v, ok = c.envConfig[strings.ToLower(key)]
 		if !ok {
 			return ""
 		}
@@ -110,7 +110,7 @@ func (c *ConfigManager) GetStringMap(key string) map[string]any {
 	defer c.mutex.RUnlock()
 	v, ok := c.combinedConfig[strings.ToLower(key)]
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
+		v, ok = c.envConfig[strings.ToLower(key)]
 		if !ok {
 			return nil
 		}
@@ -128,7 +128,7 @@ func (c *ConfigManager) GetStringSlice(key string) []string {
 	defer c.mutex.RUnlock()
 	v, ok := c.combinedConfig[strings.ToLower(key)]
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
+		v, ok = c.envConfig[strings.ToLower(key)]
 		if !ok {
 			return nil
 		}
@@ -157,7 +157,7 @@ func (c *ConfigManager) GetInt(key string) int {
 	defer c.mutex.RUnlock()
 	v, ok := c.combinedConfig[strings.ToLower(key)]
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
+		v, ok = c.envConfig[strings.ToLower(key)]
 		if !ok {
 			return 0
 		}
@@ -189,7 +189,7 @@ func (c *ConfigManager) GetIntSlice(key string) []int {
 	defer c.mutex.RUnlock()
 	v, ok := c.combinedConfig[strings.ToLower(key)]
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
+		v, ok = c.envConfig[strings.ToLower(key)]
 		if !ok {
 			return nil
 		}

jety.go

@@ -33,7 +33,6 @@ type (
 		configPath       string
 		configFileUsed   string
 		configType       configType
-		envPrefix        string
 		mapConfig        map[string]ConfigMap
 		defaultConfig    map[string]ConfigMap
 		envConfig        map[string]ConfigMap
@@ -54,7 +53,6 @@ func NewConfigManager() *ConfigManager {
 	cm.mapConfig = make(map[string]ConfigMap)
 	cm.defaultConfig = make(map[string]ConfigMap)
 	cm.combinedConfig = make(map[string]ConfigMap)
-	cm.envPrefix = ""
 	envSet := os.Environ()
 	for _, env := range envSet {
 		key, value, found := strings.Cut(env, "=")
@@ -82,8 +80,6 @@ func (c *ConfigManager) WithEnvPrefix(prefix string) *ConfigManager {
 			c.envConfig[lower] = ConfigMap{Key: withoutPrefix, Value: value}
 		}
 	}
-	// Don't set envPrefix since keys are already stripped of prefix
-	c.envPrefix = ""
 	return c
 }
 
@@ -171,7 +167,21 @@ func (c *ConfigManager) SetConfigType(configType string) error {
 func (c *ConfigManager) SetEnvPrefix(prefix string) {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
-	c.envPrefix = prefix
+	// Re-read environment variables, stripping the prefix from matching keys.
+	// This mirrors WithEnvPrefix behavior so that prefixed env vars are
+	// accessible by their unprefixed key name.
+	envSet := os.Environ()
+	c.envConfig = make(map[string]ConfigMap)
+	for _, env := range envSet {
+		key, value, found := strings.Cut(env, "=")
+		if !found {
+			continue
+		}
+		if withoutPrefix, ok := strings.CutPrefix(key, prefix); ok {
+			lower := strings.ToLower(withoutPrefix)
+			c.envConfig[lower] = ConfigMap{Key: withoutPrefix, Value: value}
+		}
+	}
 }
 
 func (c *ConfigManager) ReadInConfig() error {

jety_test.go

@@ -1,7 +1,9 @@
 package jety
 
 import (
+	"fmt"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"sync"
 	"testing"
@@ -804,11 +806,6 @@ func TestWriteConfigUnsupportedType(t *testing.T) {
 func TestSetEnvPrefix(t *testing.T) {
 	cm := NewConfigManager()
 	cm.SetEnvPrefix("PREFIX_")
-
-	// Verify it doesn't panic
-	if cm.envPrefix != "PREFIX_" {
-		t.Errorf("envPrefix = %q, want %q", cm.envPrefix, "PREFIX_")
-	}
 }
 
 func TestDeeplyNestedConfig(t *testing.T) {
@@ -1095,9 +1092,6 @@ func TestPackageLevelSetConfigName(t *testing.T) {
 func TestPackageLevelSetEnvPrefix(t *testing.T) {
 	defaultConfigManager = NewConfigManager()
 	SetEnvPrefix("JETY_TEST_")
-	if defaultConfigManager.envPrefix != "JETY_TEST_" {
-		t.Errorf("envPrefix = %q, want %q", defaultConfigManager.envPrefix, "JETY_TEST_")
-	}
 }
 
 func TestPackageLevelWriteConfig(t *testing.T) {
@@ -1266,3 +1260,90 @@ func TestDeeplyNestedWriteConfig(t *testing.T) {
 		})
 	}
 }
+
+func TestSetEnvPrefixOverridesDefault(t *testing.T) {
+	// Subprocess test: env vars must exist before NewConfigManager is called.
+	if os.Getenv("TEST_SET_ENV_PREFIX") == "1" {
+		cm := NewConfigManager()
+		cm.SetEnvPrefix("MYAPP_")
+		cm.SetDefault("port", 8080)
+
+		if got := cm.GetInt("port"); got != 9999 {
+			fmt.Fprintf(os.Stderr, "GetInt(port) = %d, want 9999\n", got)
+			os.Exit(1)
+		}
+		if got := cm.GetString("host"); got != "envhost" {
+			fmt.Fprintf(os.Stderr, "GetString(host) = %q, want %q\n", got, "envhost")
+			os.Exit(1)
+		}
+		// Unprefixed var should not be visible.
+		if got := cm.GetString("other"); got != "" {
+			fmt.Fprintf(os.Stderr, "GetString(other) = %q, want empty\n", got)
+			os.Exit(1)
+		}
+		os.Exit(0)
+	}
+
+	cmd := exec.Command(os.Args[0], "-test.run=^TestSetEnvPrefixOverridesDefault$")
+	cmd.Env = append(os.Environ(),
+		"TEST_SET_ENV_PREFIX=1",
+		"MYAPP_PORT=9999",
+		"MYAPP_HOST=envhost",
+		"OTHER=should_not_see",
+	)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("subprocess failed: %v\n%s", err, out)
+	}
+}
+
+func TestSetEnvPrefixWithSetDefault(t *testing.T) {
+	// SetDefault should pick up prefixed env vars after SetEnvPrefix.
+	if os.Getenv("TEST_SET_ENV_PREFIX_DEFAULT") == "1" {
+		cm := NewConfigManager()
+		cm.SetEnvPrefix("APP_")
+		cm.SetDefault("database_host", "localhost")
+
+		if got := cm.GetString("database_host"); got != "db.example.com" {
+			fmt.Fprintf(os.Stderr, "GetString(database_host) = %q, want %q\n", got, "db.example.com")
+			os.Exit(1)
+		}
+		os.Exit(0)
+	}
+
+	cmd := exec.Command(os.Args[0], "-test.run=^TestSetEnvPrefixWithSetDefault$")
+	cmd.Env = append(os.Environ(),
+		"TEST_SET_ENV_PREFIX_DEFAULT=1",
+		"APP_DATABASE_HOST=db.example.com",
+	)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("subprocess failed: %v\n%s", err, out)
+	}
+}
+
+func TestPackageLevelSetEnvPrefixOverrides(t *testing.T) {
+	// Package-level SetEnvPrefix should work the same way.
+	if os.Getenv("TEST_PKG_SET_ENV_PREFIX") == "1" {
+		// Reset the default manager to pick up our env vars.
+		defaultConfigManager = NewConfigManager()
+		SetEnvPrefix("PKG_")
+		SetDefault("val", "default")
+
+		if got := GetString("val"); got != "from_env" {
+			fmt.Fprintf(os.Stderr, "GetString(val) = %q, want %q\n", got, "from_env")
+			os.Exit(1)
+		}
+		os.Exit(0)
+	}
+
+	cmd := exec.Command(os.Args[0], "-test.run=^TestPackageLevelSetEnvPrefixOverrides$")
+	cmd.Env = append(os.Environ(),
+		"TEST_PKG_SET_ENV_PREFIX=1",
+		"PKG_VAL=from_env",
+	)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("subprocess failed: %v\n%s", err, out)
+	}
+}