fix: migrate module paths from forge.lthn.ai to dappco.re

Co-Authored-By: Virgil <virgil@lethean.io>

CLAUDE.md

@@ -7,9 +7,10 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 This project uses the Core CLI (`core` binary), not `go` directly.
 
 ```bash
-go test ./...                                    # run all tests
-go test -run TestConfig_Get_Good ./...           # run a single test
-go test -cover ./...                             # test with coverage
+core go test                          # run all tests
+core go test --run TestConfig_Get_Good  # run a single test
+core go cov                           # test with coverage
+core go cov --open                    # coverage + open HTML report
 
 core go qa                            # format, vet, lint, test
 core go qa full                       # adds race detector, vuln scan, security audit
@@ -33,7 +34,7 @@ This prevents environment variables from leaking into saved config files. When i
 
 **Service wrapper**: `Service` in `service.go` wraps `Config` with framework lifecycle (`core.Startable`). Both `Config` and `Service` satisfy `core.Config`, enforced by compile-time assertions.
 
-**Storage abstraction**: All file I/O goes through `io.Medium` (from `go-io`). Tests use `io.NewMockMedium()` with an in-memory `Files` map — never touch the real filesystem.
+**Storage abstraction**: All file I/O goes through `coreio.Medium` (from `go-io`). Tests use `coreio.NewMockMedium()` with an in-memory `Files` map — never touch the real filesystem.
 
 ## Conventions
 

config.go

@@ -1,6 +1,6 @@
 // Package config provides layered configuration management for the Core framework.
 //
-// Configuration values are resolved in priority order: defaults -> file -> env -> flags.
+// Configuration values are resolved in priority order: defaults -> file -> env -> Set().
 // Values are stored in a YAML file at ~/.core/config.yaml by default.
 //
 // Keys use dot notation for nested access:
@@ -11,12 +11,17 @@
 package config
 
 import (
+	"fmt"
 	"iter"
-	"maps"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
 	"sync"
 
-	core "dappco.re/go/core"
-	coreio "dappco.re/go/core/io"
+	coreio "forge.lthn.ai/core/go-io"
+	coreerr "forge.lthn.ai/core/go-log"
+	core "forge.lthn.ai/core/go/pkg/core"
 	"github.com/spf13/viper"
 	"gopkg.in/yaml.v3"
 )
@@ -25,8 +30,8 @@ import (
 // It uses viper as the underlying configuration engine.
 type Config struct {
 	mu     sync.RWMutex
-	v      *viper.Viper // Full configuration (file + env + defaults)
-	f      *viper.Viper // File-backed configuration only (for persistence)
+	full   *viper.Viper // Full configuration (file + env + defaults)
+	file   *viper.Viper // File-backed configuration only (for persistence)
 	medium coreio.Medium
 	path   string
 }
@@ -51,27 +56,22 @@ func WithPath(path string) Option {
 // WithEnvPrefix sets the prefix for environment variables.
 func WithEnvPrefix(prefix string) Option {
 	return func(c *Config) {
-		c.v.SetEnvPrefix(prefix)
+		c.full.SetEnvPrefix(strings.TrimSuffix(prefix, "_"))
 	}
 }
 
-// dotReplacer implements viper.StringReplacer, converting dots to underscores
-// for environment variable key mapping without importing strings directly.
-type dotReplacer struct{}
-
-func (dotReplacer) Replace(s string) string { return core.Replace(s, ".", "_") }
-
 // New creates a new Config instance with the given options.
 // If no medium is provided, it defaults to io.Local.
 // If no path is provided, it defaults to ~/.core/config.yaml.
 func New(opts ...Option) (*Config, error) {
 	c := &Config{
-		v: viper.NewWithOptions(viper.EnvKeyReplacer(dotReplacer{})),
-		f: viper.New(),
+		full: viper.New(),
+		file: viper.New(),
 	}
 
 	// Configure viper defaults
-	c.v.SetEnvPrefix("CORE_CONFIG")
+	c.full.SetEnvPrefix("CORE_CONFIG")
+	c.full.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
 
 	for _, opt := range opts {
 		opt(c)
@@ -82,54 +82,79 @@ func New(opts ...Option) (*Config, error) {
 	}
 
 	if c.path == "" {
-		home := core.Env("DIR_HOME")
-		if home == "" {
-			return nil, core.E("config.New", "failed to determine home directory", nil)
+		home, err := os.UserHomeDir()
+		if err != nil {
+			return nil, coreerr.E("config.New", "failed to determine home directory", err)
 		}
-		c.path = core.Path(home, ".core", "config.yaml")
+		c.path = filepath.Join(home, ".core", "config.yaml")
 	}
 
-	c.v.AutomaticEnv()
+	c.full.AutomaticEnv()
 
 	// Load existing config file if it exists
 	if c.medium.Exists(c.path) {
 		if err := c.LoadFile(c.medium, c.path); err != nil {
-			return nil, core.E("config.New", "failed to load config file", err)
+			return nil, coreerr.E("config.New", "failed to load config file", err)
 		}
 	}
 
 	return c, nil
 }
 
+func configTypeForPath(path string) (string, error) {
+	ext := strings.ToLower(filepath.Ext(path))
+	if ext == "" && filepath.Base(path) == ".env" {
+		return "env", nil
+	}
+	if ext == "" {
+		return "yaml", nil
+	}
+
+	switch ext {
+	case ".yaml", ".yml":
+		return "yaml", nil
+	case ".json":
+		return "json", nil
+	case ".toml":
+		return "toml", nil
+	case ".env":
+		return "env", nil
+	default:
+		return "", coreerr.E("config.configTypeForPath", "unsupported config file type: "+path, nil)
+	}
+}
+
 // LoadFile reads a configuration file from the given medium and path and merges it into the current config.
-// It supports YAML and environment files (.env).
+// It supports YAML, JSON, TOML, and dotenv files (.env).
 func (c *Config) LoadFile(m coreio.Medium, path string) error {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 
+	configType, err := configTypeForPath(path)
+	if err != nil {
+		return coreerr.E("config.LoadFile", "failed to determine config file type: "+path, err)
+	}
+
 	content, err := m.Read(path)
 	if err != nil {
-		return core.E("config.LoadFile", "failed to read config file: "+path, err)
+		return coreerr.E("config.LoadFile", fmt.Sprintf("failed to read config file: %s", path), err)
 	}
 
-	ext := core.PathExt(path)
-	configType := "yaml"
-	if ext == "" && core.PathBase(path) == ".env" {
-		configType = "env"
-	} else if ext != "" {
-		configType = core.TrimPrefix(ext, ".")
+	parsed := viper.New()
+	parsed.SetConfigType(configType)
+	if err := parsed.MergeConfig(strings.NewReader(content)); err != nil {
+		return coreerr.E("config.LoadFile", fmt.Sprintf("failed to parse config file: %s", path), err)
 	}
 
-	// Load into file-backed viper
-	c.f.SetConfigType(configType)
-	if err := c.f.MergeConfig(core.NewReader(content)); err != nil {
-		return core.E("config.LoadFile", "failed to parse config file (f): "+path, err)
+	settings := parsed.AllSettings()
+
+	// Keep the persisted and runtime views aligned with the same parsed data.
+	if err := c.file.MergeConfigMap(settings); err != nil {
+		return coreerr.E("config.LoadFile", "failed to merge config into file settings", err)
 	}
 
-	// Load into full viper
-	c.v.SetConfigType(configType)
-	if err := c.v.MergeConfig(core.NewReader(content)); err != nil {
-		return core.E("config.LoadFile", "failed to parse config file (v): "+path, err)
+	if err := c.full.MergeConfigMap(settings); err != nil {
+		return coreerr.E("config.LoadFile", "failed to merge config into full settings", err)
 	}
 
 	return nil
@@ -143,18 +168,18 @@ func (c *Config) Get(key string, out any) error {
 	defer c.mu.RUnlock()
 
 	if key == "" {
-		if err := c.v.Unmarshal(out); err != nil {
-			return core.E("config.Get", "failed to unmarshal full config", err)
+		if err := c.full.Unmarshal(out); err != nil {
+			return coreerr.E("config.Get", "failed to unmarshal full config", err)
 		}
 		return nil
 	}
 
-	if !c.v.IsSet(key) {
-		return core.E("config.Get", "key not found: "+key, nil)
+	if !c.full.IsSet(key) {
+		return coreerr.E("config.Get", fmt.Sprintf("key not found: %s", key), nil)
 	}
 
-	if err := c.v.UnmarshalKey(key, out); err != nil {
-		return core.E("config.Get", "failed to unmarshal key: "+key, err)
+	if err := c.full.UnmarshalKey(key, out); err != nil {
+		return coreerr.E("config.Get", fmt.Sprintf("failed to unmarshal key: %s", key), err)
 	}
 	return nil
 }
@@ -165,8 +190,8 @@ func (c *Config) Set(key string, v any) error {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 
-	c.f.Set(key, v)
-	c.v.Set(key, v)
+	c.file.Set(key, v)
+	c.full.Set(key, v)
 	return nil
 }
 
@@ -177,17 +202,32 @@ func (c *Config) Commit() error {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 
-	if err := Save(c.medium, c.path, c.f.AllSettings()); err != nil {
-		return core.E("config.Commit", "failed to save config", err)
+	if err := Save(c.medium, c.path, c.file.AllSettings()); err != nil {
+		return coreerr.E("config.Commit", "failed to save config", err)
 	}
 	return nil
 }
 
-// All returns an iterator over all configuration values (including environment variables).
+// All returns an iterator over all configuration values in lexical key order
+// (including environment variables).
 func (c *Config) All() iter.Seq2[string, any] {
 	c.mu.RLock()
 	defer c.mu.RUnlock()
-	return maps.All(c.v.AllSettings())
+
+	settings := c.full.AllSettings()
+	keys := make([]string, 0, len(settings))
+	for key := range settings {
+		keys = append(keys, key)
+	}
+	sort.Strings(keys)
+
+	return func(yield func(string, any) bool) {
+		for _, key := range keys {
+			if !yield(key, settings[key]) {
+				return
+			}
+		}
+	}
 }
 
 // Path returns the path to the configuration file.
@@ -199,15 +239,22 @@ func (c *Config) Path() string {
 // Returns the parsed data as a map, or an error if the file cannot be read or parsed.
 // Deprecated: Use Config.LoadFile instead.
 func Load(m coreio.Medium, path string) (map[string]any, error) {
+	switch ext := strings.ToLower(filepath.Ext(path)); ext {
+	case "", ".yaml", ".yml":
+		// These paths are safe to treat as YAML sources.
+	default:
+		return nil, coreerr.E("config.Load", "unsupported config file type: "+path, nil)
+	}
+
 	content, err := m.Read(path)
 	if err != nil {
-		return nil, core.E("config.Load", "failed to read config file: "+path, err)
+		return nil, coreerr.E("config.Load", "failed to read config file: "+path, err)
 	}
 
 	v := viper.New()
 	v.SetConfigType("yaml")
-	if err := v.ReadConfig(core.NewReader(content)); err != nil {
-		return nil, core.E("config.Load", "failed to parse config file: "+path, err)
+	if err := v.ReadConfig(strings.NewReader(content)); err != nil {
+		return nil, coreerr.E("config.Load", "failed to parse config file: "+path, err)
 	}
 
 	return v.AllSettings(), nil
@@ -216,20 +263,29 @@ func Load(m coreio.Medium, path string) (map[string]any, error) {
 // Save writes configuration data to a YAML file at the given path.
 // It ensures the parent directory exists before writing.
 func Save(m coreio.Medium, path string, data map[string]any) error {
-	out, err := yaml.Marshal(data)
-	if err != nil {
-		return core.E("config.Save", "failed to marshal config", err)
+	switch ext := strings.ToLower(filepath.Ext(path)); ext {
+	case "", ".yaml", ".yml":
+		// These paths are safe to treat as YAML destinations.
+	default:
+		return coreerr.E("config.Save", "unsupported config file type: "+path, nil)
 	}
 
-	dir := core.PathDir(path)
+	out, err := yaml.Marshal(data)
+	if err != nil {
+		return coreerr.E("config.Save", "failed to marshal config", err)
+	}
+
+	dir := filepath.Dir(path)
 	if err := m.EnsureDir(dir); err != nil {
-		return core.E("config.Save", "failed to create config directory: "+dir, err)
+		return coreerr.E("config.Save", "failed to create config directory: "+dir, err)
 	}
 
 	if err := m.Write(path, string(out)); err != nil {
-		return core.E("config.Save", "failed to write config file: "+path, err)
+		return coreerr.E("config.Save", "failed to write config file: "+path, err)
 	}
 
 	return nil
 }
 
+// Ensure Config implements core.Config at compile time.
+var _ core.Config = (*Config)(nil)

config_test.go

@@ -1,11 +1,14 @@
 package config
 
 import (
+	"context"
+	"fmt"
 	"maps"
+	"os"
 	"testing"
 
-	core "dappco.re/go/core"
-	coreio "dappco.re/go/core/io"
+	coreio "forge.lthn.ai/core/go-io"
+	core "forge.lthn.ai/core/go/pkg/core"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -89,6 +92,23 @@ func TestConfig_All_Good(t *testing.T) {
 	assert.Equal(t, "val2", all["key2"])
 }
 
+func TestConfig_All_Order_Good(t *testing.T) {
+	m := coreio.NewMockMedium()
+
+	cfg, err := New(WithMedium(m), WithPath("/tmp/test/config.yaml"))
+	assert.NoError(t, err)
+
+	_ = cfg.Set("zulu", "last")
+	_ = cfg.Set("alpha", "first")
+
+	var keys []string
+	for key, _ := range cfg.All() {
+		keys = append(keys, key)
+	}
+
+	assert.Equal(t, []string{"alpha", "zulu"}, keys)
+}
+
 func TestConfig_Path_Good(t *testing.T) {
 	m := coreio.NewMockMedium()
 
@@ -185,7 +205,7 @@ func TestConfig_DefaultPath_Good(t *testing.T) {
 	cfg, err := New(WithMedium(m))
 	assert.NoError(t, err)
 
-	home := core.Env("DIR_HOME")
+	home, _ := os.UserHomeDir()
 	assert.Equal(t, home+"/.core/config.yaml", cfg.Path())
 }
 
@@ -198,6 +218,21 @@ func TestLoadEnv_Good(t *testing.T) {
 	assert.Equal(t, "value", result["simple"])
 }
 
+func TestLoadEnv_PrefixNormalisation_Good(t *testing.T) {
+	t.Setenv("MYAPP_SETTING", "secret")
+	t.Setenv("MYAPP_ALPHA", "first")
+
+	keys := make([]string, 0, 2)
+	values := make([]string, 0, 2)
+	for key, value := range Env("MYAPP") {
+		keys = append(keys, key)
+		values = append(values, value.(string))
+	}
+
+	assert.Equal(t, []string{"alpha", "setting"}, keys)
+	assert.Equal(t, []string{"first", "secret"}, values)
+}
+
 func TestLoad_Bad(t *testing.T) {
 	m := coreio.NewMockMedium()
 
@@ -206,6 +241,15 @@ func TestLoad_Bad(t *testing.T) {
 	assert.Contains(t, err.Error(), "failed to read config file")
 }
 
+func TestLoad_UnsupportedPath_Bad(t *testing.T) {
+	m := coreio.NewMockMedium()
+	m.Files["/tmp/test/config.json"] = `{"app":{"name":"core"}}`
+
+	_, err := Load(m, "/tmp/test/config.json")
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "unsupported config file type")
+}
+
 func TestLoad_InvalidYAML_Bad(t *testing.T) {
 	m := coreio.NewMockMedium()
 	m.Files["/tmp/test/config.yaml"] = "invalid: yaml: content: [[[["
@@ -215,6 +259,68 @@ func TestLoad_InvalidYAML_Bad(t *testing.T) {
 	assert.Contains(t, err.Error(), "failed to parse config file")
 }
 
+func TestConfig_LoadFile_JSON_Good(t *testing.T) {
+	m := coreio.NewMockMedium()
+	m.Files["/tmp/test/config.json"] = `{"app":{"name":"core"}}`
+
+	cfg, err := New(WithMedium(m), WithPath("/tmp/test/config.json"))
+	assert.NoError(t, err)
+
+	var name string
+	err = cfg.Get("app.name", &name)
+	assert.NoError(t, err)
+	assert.Equal(t, "core", name)
+}
+
+func TestConfig_LoadFile_Extensionless_Good(t *testing.T) {
+	m := coreio.NewMockMedium()
+	m.Files["/tmp/test/config"] = "app:\n  name: core\n"
+
+	cfg, err := New(WithMedium(m), WithPath("/tmp/test/config"))
+	assert.NoError(t, err)
+
+	var name string
+	err = cfg.Get("app.name", &name)
+	assert.NoError(t, err)
+	assert.Equal(t, "core", name)
+}
+
+func TestConfig_LoadFile_TOML_Good(t *testing.T) {
+	m := coreio.NewMockMedium()
+	m.Files["/tmp/test/config.toml"] = "app = { name = \"core\" }\n"
+
+	cfg, err := New(WithMedium(m), WithPath("/tmp/test/config.toml"))
+	assert.NoError(t, err)
+
+	var name string
+	err = cfg.Get("app.name", &name)
+	assert.NoError(t, err)
+	assert.Equal(t, "core", name)
+}
+
+func TestConfig_LoadFile_Unsupported_Bad(t *testing.T) {
+	m := coreio.NewMockMedium()
+
+	cfg, err := New(WithMedium(m), WithPath("/tmp/test/config.txt"))
+	assert.NoError(t, err)
+
+	m.Files["/tmp/test/config.txt"] = "app.name=core"
+	err = cfg.LoadFile(m, "/tmp/test/config.txt")
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "unsupported config file type")
+}
+
+func TestConfig_LoadFile_Unsupported_NoRead_Bad(t *testing.T) {
+	m := coreio.NewMockMedium()
+
+	cfg, err := New(WithMedium(m), WithPath("/tmp/test/config.txt"))
+	assert.NoError(t, err)
+
+	err = cfg.LoadFile(m, "/tmp/test/config.txt")
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "unsupported config file type")
+}
+
 func TestSave_Good(t *testing.T) {
 	m := coreio.NewMockMedium()
 
@@ -230,6 +336,39 @@ func TestSave_Good(t *testing.T) {
 	assert.Contains(t, content, "key: value")
 }
 
+func TestSave_Extensionless_Good(t *testing.T) {
+	m := coreio.NewMockMedium()
+
+	err := Save(m, "/tmp/test/config", map[string]any{"key": "value"})
+	assert.NoError(t, err)
+
+	content, readErr := m.Read("/tmp/test/config")
+	assert.NoError(t, readErr)
+	assert.Contains(t, content, "key: value")
+}
+
+func TestSave_UnsupportedPath_Bad(t *testing.T) {
+	m := coreio.NewMockMedium()
+
+	err := Save(m, "/tmp/test/config.json", map[string]any{"key": "value"})
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "unsupported config file type")
+}
+
+func TestConfig_Commit_UnsupportedPath_Bad(t *testing.T) {
+	m := coreio.NewMockMedium()
+
+	cfg, err := New(WithMedium(m), WithPath("/tmp/test/config.json"))
+	assert.NoError(t, err)
+
+	err = cfg.Set("key", "value")
+	assert.NoError(t, err)
+
+	err = cfg.Commit()
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "unsupported config file type")
+}
+
 func TestConfig_LoadFile_Env(t *testing.T) {
 	m := coreio.NewMockMedium()
 	m.Files["/.env"] = "FOO=bar\nBAZ=qux"
@@ -259,6 +398,39 @@ func TestConfig_WithEnvPrefix(t *testing.T) {
 	assert.Equal(t, "secret", setting)
 }
 
+func TestConfig_WithEnvPrefix_TrailingUnderscore_Good(t *testing.T) {
+	t.Setenv("MYAPP_SETTING", "secret")
+
+	m := coreio.NewMockMedium()
+	cfg, err := New(WithMedium(m), WithEnvPrefix("MYAPP_"))
+	assert.NoError(t, err)
+
+	var setting string
+	err = cfg.Get("setting", &setting)
+	assert.NoError(t, err)
+	assert.Equal(t, "secret", setting)
+}
+
+func TestService_OnStartup_WithEnvPrefix_Good(t *testing.T) {
+	t.Setenv("MYAPP_SETTING", "secret")
+
+	m := coreio.NewMockMedium()
+	svc := &Service{
+		ServiceRuntime: core.NewServiceRuntime(nil, ServiceOptions{
+			EnvPrefix: "MYAPP",
+			Medium:    m,
+		}),
+	}
+
+	err := svc.OnStartup(context.Background())
+	assert.NoError(t, err)
+
+	var setting string
+	err = svc.Get("setting", &setting)
+	assert.NoError(t, err)
+	assert.Equal(t, "secret", setting)
+}
+
 func TestConfig_Get_EmptyKey(t *testing.T) {
 	m := coreio.NewMockMedium()
 	m.Files["/config.yaml"] = "app:\n  name: test\nversion: 1"
@@ -279,3 +451,56 @@ func TestConfig_Get_EmptyKey(t *testing.T) {
 	assert.Equal(t, "test", full.App.Name)
 	assert.Equal(t, 1, full.Version)
 }
+
+func ExampleConfig_Get() {
+	m := coreio.NewMockMedium()
+
+	cfg, _ := New(WithMedium(m), WithPath("/tmp/example/config.yaml"))
+	_ = cfg.Set("dev.editor", "vim")
+
+	var editor string
+	_ = cfg.Get("dev.editor", &editor)
+
+	fmt.Println(editor)
+	// Output: vim
+}
+
+func ExampleConfig_Commit() {
+	m := coreio.NewMockMedium()
+
+	cfg, _ := New(WithMedium(m), WithPath("/tmp/example/config.yaml"))
+	_ = cfg.Set("app.name", "core")
+	_ = cfg.Commit()
+
+	content, _ := m.Read("/tmp/example/config.yaml")
+	fmt.Print(content)
+	// Output:
+	// app:
+	//     name: core
+}
+
+func ExampleEnv() {
+	t := "EXAMPLE_FOO_BAR"
+	_ = os.Setenv(t, "baz")
+	defer os.Unsetenv(t)
+
+	for key, value := range Env("EXAMPLE_") {
+		fmt.Printf("%s=%s\n", key, value)
+	}
+
+	// Output: foo.bar=baz
+}
+
+func ExampleConfig_LoadFile() {
+	m := coreio.NewMockMedium()
+	m.Files["/.env"] = "FOO=bar\n"
+
+	cfg, _ := New(WithMedium(m), WithPath("/config.yaml"))
+	_ = cfg.LoadFile(m, "/.env")
+
+	var foo string
+	_ = cfg.Get("foo", &foo)
+
+	fmt.Println(foo)
+	// Output: bar
+}

docs/architecture.md

@@ -19,8 +19,8 @@ description: Internal design of config -- dual-viper layering, the Medium abstra
 ```go
 type Config struct {
     mu     sync.RWMutex
-    v      *viper.Viper   // full configuration (file + env + defaults)
-    f      *viper.Viper   // file-backed configuration only (for persistence)
+    full   *viper.Viper   // full configuration (file + env + defaults)
+    file   *viper.Viper   // file-backed configuration only (for persistence)
     medium coreio.Medium
     path   string
 }
@@ -28,10 +28,10 @@ type Config struct {
 
 `Config` is the central type. It holds **two** Viper instances:
 
-- **`v`** (full) -- contains everything: file values, environment bindings, and explicit `Set()` calls. All reads go through `v`.
-- **`f`** (file) -- contains only values that originated from the config file or were explicitly set via `Set()`. All writes (`Commit()`) go through `f`.
+- **`full`** -- contains everything: file values, environment bindings, and explicit `Set()` calls. All reads go through `full`.
+- **`file`** -- contains only values that originated from the config file or were explicitly set via `Set()`. All writes (`Commit()`) go through `file`.
 
-This dual-instance design is the key architectural decision. It solves the environment leakage problem: Viper merges environment variables into its settings map, which means a naive `SaveConfig()` would serialise env vars into the YAML file. By maintaining `f` as a clean copy, `Commit()` only persists what should be persisted.
+This dual-instance design is the key architectural decision. It solves the environment leakage problem: Viper merges environment variables into its settings map, which means a naive `SaveConfig()` would serialise env vars into the YAML file. By maintaining `file` as a clean copy, `Commit()` only persists what should be persisted.
 
 ### Option
 
@@ -91,19 +91,19 @@ func LoadEnv(prefix string) map[string]any  // deprecated
 ```
 New(opts...)
   |
-  +-- create two viper instances (v, f)
-  +-- set env prefix on v ("CORE_CONFIG_" default)
+  +-- create two viper instances (full, file)
+  +-- set env prefix on full ("CORE_CONFIG_" default)
   +-- set env key replacer ("." <-> "_")
   +-- apply functional options
   +-- default medium to io.Local if nil
   +-- default path to ~/.core/config.yaml if empty
-  +-- enable v.AutomaticEnv()
+  +-- enable full.AutomaticEnv()
   +-- if config file exists:
         LoadFile(medium, path)
           +-- medium.Read(path)
           +-- detect config type from extension
-          +-- f.MergeConfig(content)
-          +-- v.MergeConfig(content)
+          +-- file.MergeConfig(content)
+          +-- full.MergeConfig(content)
 ```
 
 ### Read (`Get`)
@@ -113,15 +113,15 @@ Get(key, &out)
   |
   +-- RLock
   +-- if key == "":
-  |     v.Unmarshal(out)     // full config into a struct
+  |     full.Unmarshal(out)  // full config into a struct
   +-- else:
-  |     v.IsSet(key)?
-  |       yes -> v.UnmarshalKey(key, out)
+  |     full.IsSet(key)?
+  |       yes -> full.UnmarshalKey(key, out)
   |       no  -> error "key not found"
   +-- RUnlock
 ```
 
-Because `v` has `AutomaticEnv()` enabled, `v.IsSet(key)` returns true if the key exists in the file **or** as a `CORE_CONFIG_*` environment variable.
+Because `full` has `AutomaticEnv()` enabled, `full.IsSet(key)` returns true if the key exists in the file **or** as a `CORE_CONFIG_*` environment variable.
 
 ### Write (`Set` + `Commit`)
 
@@ -129,32 +129,32 @@ Because `v` has `AutomaticEnv()` enabled, `v.IsSet(key)` returns true if the key
 Set(key, value)
   |
   +-- Lock
-  +-- f.Set(key, value)   // track for persistence
-  +-- v.Set(key, value)   // make visible to Get()
+  +-- file.Set(key, value)  // track for persistence
+  +-- full.Set(key, value)   // make visible to Get()
   +-- Unlock
 
 Commit()
   |
   +-- Lock
-  +-- Save(medium, path, f.AllSettings())
+  +-- Save(medium, path, file.AllSettings())
   |     +-- yaml.Marshal(data)
   |     +-- medium.EnsureDir(dir)
   |     +-- medium.Write(path, content)
   +-- Unlock
 ```
 
-Note that `Commit()` serialises `f.AllSettings()`, not `v.AllSettings()`. This is intentional -- it prevents environment variable values from being written to the config file.
+Note that `Commit()` serialises `file.AllSettings()`, not `full.AllSettings()`. This is intentional -- it prevents environment variable values from being written to the config file.
 
 ### File Loading (`LoadFile`)
 
-`LoadFile` supports both YAML and `.env` files. The config type is inferred from the file extension:
+`LoadFile` supports YAML, JSON, TOML, and `.env` files. The config type is inferred from the file extension:
 
 - `.yaml`, `.yml` -- YAML
 - `.json` -- JSON
 - `.toml` -- TOML
 - `.env` (no extension, basename `.env`) -- dotenv format
 
-Content is merged (not replaced) into both `v` and `f` via `MergeConfig`, so multiple files can be layered.
+Content is merged (not replaced) into both `full` and `file` via `MergeConfig`, so multiple files can be layered.
 
 ## Concurrency
 

docs/index.md

@@ -5,7 +5,7 @@ description: Layered configuration management for the Core framework with file,
 
 # config
 
-`forge.lthn.ai/core/config` provides layered configuration management for applications built on the Core framework. It resolves values through a priority chain -- defaults, file, environment variables, flags -- so that the same codebase works identically across local development, CI, and production without code changes.
+`forge.lthn.ai/core/config` provides layered configuration management for applications built on the Core framework. It resolves values through a priority chain -- defaults, file, environment variables, and explicit `Set()` calls -- so that the same codebase works identically across local development, CI, and production without code changes.
 
 ## Module Path
 

env.go

@@ -3,24 +3,42 @@ package config
 import (
 	"iter"
 	"os"
-
-	core "dappco.re/go/core"
+	"sort"
+	"strings"
 )
 
+func normaliseEnvPrefix(prefix string) string {
+	if prefix == "" || strings.HasSuffix(prefix, "_") {
+		return prefix
+	}
+	return prefix + "_"
+}
+
 // Env returns an iterator over environment variables with the given prefix,
 // providing them as dot-notation keys and values.
 //
+// The prefix may be supplied with or without a trailing underscore.
+//
 // For example, with prefix "CORE_CONFIG_":
 //
 //	CORE_CONFIG_FOO_BAR=baz  -> yields ("foo.bar", "baz")
 func Env(prefix string) iter.Seq2[string, any] {
 	return func(yield func(string, any) bool) {
+		prefix = normaliseEnvPrefix(prefix)
+
+		type entry struct {
+			key   string
+			value any
+		}
+
+		var entries []entry
+
 		for _, env := range os.Environ() {
-			if !core.HasPrefix(env, prefix) {
+			if !strings.HasPrefix(env, prefix) {
 				continue
 			}
 
-			parts := core.SplitN(env, "=", 2)
+			parts := strings.SplitN(env, "=", 2)
 			if len(parts) != 2 {
 				continue
 			}
@@ -28,12 +46,19 @@ func Env(prefix string) iter.Seq2[string, any] {
 			name := parts[0]
 			value := parts[1]
 
-			// Strip prefix and convert to dot notation
-			key := core.TrimPrefix(name, prefix)
-			key = core.Lower(key)
-			key = core.Replace(key, "_", ".")
+			key := strings.TrimPrefix(name, prefix)
+			key = strings.ToLower(key)
+			key = strings.ReplaceAll(key, "_", ".")
 
-			if !yield(key, value) {
+			entries = append(entries, entry{key: key, value: value})
+		}
+
+		sort.Slice(entries, func(i, j int) bool {
+			return entries[i].key < entries[j].key
+		})
+
+		for _, entry := range entries {
+			if !yield(entry.key, entry.value) {
 				return
 			}
 		}

go.mod

@@ -1,17 +1,17 @@
-module forge.lthn.ai/core/config
+module dappco.re/go/core/config
 
 go 1.26.0
 
 require (
-	dappco.re/go/core v0.8.0-alpha.1
-	dappco.re/go/core/io v0.2.0
+	dappco.re/go/core v0.3.3
+	dappco.re/go/core/io v0.1.7
+	dappco.re/go/core/log v0.0.4
 	github.com/spf13/viper v1.21.0
 	github.com/stretchr/testify v1.11.1
 	gopkg.in/yaml.v3 v3.0.1
 )
 
 require (
-	forge.lthn.ai/core/go-log v0.0.4 // indirect
 	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
 	github.com/fsnotify/fsnotify v1.9.0 // indirect
 	github.com/go-viper/mapstructure/v2 v2.5.0 // indirect

go.sum

@@ -1,7 +1,7 @@
-dappco.re/go/core v0.8.0-alpha.1 h1:gj7+Scv+L63Z7wMxbJYHhaRFkHJo2u4MMPuUSv/Dhtk=
-dappco.re/go/core v0.8.0-alpha.1/go.mod h1:f2/tBZ3+3IqDrg2F5F598llv0nmb/4gJVCFzM5geE4A=
-dappco.re/go/core/io v0.2.0 h1:zuudgIiTsQQ5ipVt97saWdGLROovbEB/zdVyy9/l+I4=
-dappco.re/go/core/io v0.2.0/go.mod h1:1QnQV6X9LNgFKfm8SkOtR9LLaj3bDcsOIeJOOyjbL5E=
+forge.lthn.ai/core/go v0.3.3 h1:kYYZ2nRYy0/Be3cyuLJspRjLqTMxpckVyhb/7Sw2gd0=
+forge.lthn.ai/core/go v0.3.3/go.mod h1:Cp4ac25pghvO2iqOu59t1GyngTKVOzKB5/VPdhRi9CQ=
+forge.lthn.ai/core/go-io v0.1.7 h1:Tdb6sqh+zz1lsGJaNX9RFWM6MJ/RhSAyxfulLXrJsbk=
+forge.lthn.ai/core/go-io v0.1.7/go.mod h1:8lRLFk4Dnp5cR/Cyzh9WclD5566TbpdRgwcH7UZLWn4=
 forge.lthn.ai/core/go-log v0.0.4 h1:KTuCEPgFmuM8KJfnyQ8vPOU1Jg654W74h8IJvfQMfv0=
 forge.lthn.ai/core/go-log v0.0.4/go.mod h1:r14MXKOD3LF/sI8XUJQhRk/SZHBE7jAFVuCfgkXoZPw=
 github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc h1:U9qPSI2PIWSS1VwoXQT9A3Wy9MM3WgvqSxFWenqJduM=

service.go

@@ -3,8 +3,9 @@ package config
 import (
 	"context"
 
-	core "dappco.re/go/core"
-	coreio "dappco.re/go/core/io"
+	coreio "forge.lthn.ai/core/go-io"
+	coreerr "forge.lthn.ai/core/go-log"
+	core "forge.lthn.ai/core/go/pkg/core"
 )
 
 // Service wraps Config as a framework service with lifecycle support.
@@ -17,44 +18,49 @@ type Service struct {
 type ServiceOptions struct {
 	// Path overrides the default config file path.
 	Path string
+	// EnvPrefix overrides the default environment variable prefix.
+	EnvPrefix string
 	// Medium overrides the default storage medium.
 	Medium coreio.Medium
 }
 
 // NewConfigService creates a new config service factory for the Core framework.
 // Register it with core.WithService(config.NewConfigService).
-func NewConfigService(c *core.Core) core.Result {
+func NewConfigService(c *core.Core) (any, error) {
 	svc := &Service{
 		ServiceRuntime: core.NewServiceRuntime(c, ServiceOptions{}),
 	}
-	return core.Result{Value: svc, OK: true}
+	return svc, nil
 }
 
 // OnStartup loads the configuration file during application startup.
-func (s *Service) OnStartup(_ context.Context) core.Result {
-	opts := s.Options()
+func (s *Service) OnStartup(_ context.Context) error {
+	opts := s.Opts()
 
 	var configOpts []Option
 	if opts.Path != "" {
 		configOpts = append(configOpts, WithPath(opts.Path))
 	}
+	if opts.EnvPrefix != "" {
+		configOpts = append(configOpts, WithEnvPrefix(opts.EnvPrefix))
+	}
 	if opts.Medium != nil {
 		configOpts = append(configOpts, WithMedium(opts.Medium))
 	}
 
 	cfg, err := New(configOpts...)
 	if err != nil {
-		return core.Result{Value: core.E("config.Service.OnStartup", "failed to create config", err)}
+		return coreerr.E("config.Service.OnStartup", "failed to create config", err)
 	}
 
 	s.config = cfg
-	return core.Result{OK: true}
+	return nil
 }
 
 // Get retrieves a configuration value by key.
 func (s *Service) Get(key string, out any) error {
 	if s.config == nil {
-		return core.E("config.Service.Get", "config not loaded", nil)
+		return coreerr.E("config.Service.Get", "config not loaded", nil)
 	}
 	return s.config.Get(key, out)
 }
@@ -62,7 +68,7 @@ func (s *Service) Get(key string, out any) error {
 // Set stores a configuration value by key.
 func (s *Service) Set(key string, v any) error {
 	if s.config == nil {
-		return core.E("config.Service.Set", "config not loaded", nil)
+		return coreerr.E("config.Service.Set", "config not loaded", nil)
 	}
 	return s.config.Set(key, v)
 }
@@ -70,7 +76,7 @@ func (s *Service) Set(key string, v any) error {
 // Commit persists any configuration changes to disk.
 func (s *Service) Commit() error {
 	if s.config == nil {
-		return core.E("config.Service.Commit", "config not loaded", nil)
+		return coreerr.E("config.Service.Commit", "config not loaded", nil)
 	}
 	return s.config.Commit()
 }
@@ -78,10 +84,13 @@ func (s *Service) Commit() error {
 // LoadFile merges a configuration file into the central configuration.
 func (s *Service) LoadFile(m coreio.Medium, path string) error {
 	if s.config == nil {
-		return core.E("config.Service.LoadFile", "config not loaded", nil)
+		return coreerr.E("config.Service.LoadFile", "config not loaded", nil)
 	}
 	return s.config.LoadFile(m, path)
 }
 
-// Ensure Service implements core.Startable at compile time.
-var _ core.Startable = (*Service)(nil)
+// Ensure Service implements core.Config and Startable at compile time.
+var (
+	_ core.Config    = (*Service)(nil)
+	_ core.Startable = (*Service)(nil)
+)