feat(config): expose service env prefix option

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

config_test.go

@@ -1,12 +1,14 @@
 package config
 
 import (
+	"context"
 	"fmt"
 	"maps"
 	"os"
 	"testing"
 
 	coreio "forge.lthn.ai/core/go-io"
+	core "forge.lthn.ai/core/go/pkg/core"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -409,6 +411,26 @@ func TestConfig_WithEnvPrefix_TrailingUnderscore_Good(t *testing.T) {
 	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"

service.go

@@ -18,6 +18,8 @@ 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
 }
@@ -39,6 +41,9 @@ func (s *Service) OnStartup(_ context.Context) error {
 	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))
 	}