feat: OS-aware agent config directory

agent/internal/config/config.go

@@ -2,12 +2,26 @@ package config
 
 import (
 	"os"
+	"path/filepath"
+	"runtime"
 	"time"
 
 	"gopkg.in/yaml.v3"
 )
 
-const ConfigPath = "/etc/vantage/config.yaml"
+// ConfigDir returns the platform-specific config directory.
+func ConfigDir() string {
+	if runtime.GOOS == "windows" {
+		base := os.Getenv("ProgramData")
+		if base == "" {
+			base = `C:\ProgramData`
+		}
+		return filepath.Join(base, "vantage")
+	}
+	return "/etc/vantage"
+}
+
+func configPath() string { return filepath.Join(ConfigDir(), "config.yaml") }
 
 type Config struct {
 	ServerURL    string        `yaml:"server_url"`
@@ -19,7 +33,7 @@ type Config struct {
 }
 
 func Load() (*Config, error) {
-	data, err := os.ReadFile(ConfigPath)
+	data, err := os.ReadFile(configPath())
 	if err != nil {
 		return nil, err
 	}
@@ -38,8 +52,8 @@ func Save(cfg *Config) error {
 	if err != nil {
 		return err
 	}
-	if err := os.MkdirAll("/etc/vantage", 0700); err != nil {
+	if err := os.MkdirAll(ConfigDir(), 0700); err != nil {
 		return err
 	}
-	return os.WriteFile(ConfigPath, data, 0600)
+	return os.WriteFile(configPath(), data, 0600)
 }

agent/internal/config/config_test.go

@@ -0,0 +1,20 @@
+package config
+
+import (
+	"runtime"
+	"strings"
+	"testing"
+)
+
+func TestConfigDirByOS(t *testing.T) {
+	d := ConfigDir()
+	if runtime.GOOS == "windows" {
+		if !strings.Contains(strings.ToLower(d), "programdata") {
+			t.Fatalf("windows config dir = %q, want ProgramData path", d)
+		}
+	} else {
+		if d != "/etc/vantage" {
+			t.Fatalf("unix config dir = %q, want /etc/vantage", d)
+		}
+	}
+}