refactor: switch config format from YAML to TOML

- Replace gopkg.in/yaml.v3 with github.com/BurntSushi/toml
- Update struct tags from yaml to toml
- Update config tests to use TOML syntax
- Add testdata/config.toml, update Helm configmap template

internal/config/config.go

@@ -6,39 +6,39 @@ import (
 	"regexp"
 	"strings"
 
-	"gopkg.in/yaml.v3"
+	"github.com/BurntSushi/toml"
 )
 
 type Config struct {
-	Server ServerConfig `yaml:"server"`
-	Git    GitConfig    `yaml:"git"`
-	Cluster ClusterConfig `yaml:"cluster"`
-	ToolchainRegistry string `yaml:"toolchain_registry"`
-	TargetRepoTemplate string `yaml:"target_repo_template"`
-	Plugins []PluginConfig `yaml:"plugins"`
+	Server             ServerConfig   `toml:"server"`
+	Git                GitConfig      `toml:"git"`
+	Cluster            ClusterConfig  `toml:"cluster"`
+	ToolchainRegistry  string         `toml:"toolchain_registry"`
+	TargetRepoTemplate string         `toml:"target_repo_template"`
+	Plugins            []PluginConfig `toml:"plugins"`
 }
 
 type ServerConfig struct {
-	Addr      string `yaml:"addr"`
-	PublicURL string `yaml:"public_url"`
+	Addr      string `toml:"addr"`
+	PublicURL string `toml:"public_url"`
 }
 
 type GitConfig struct {
-	Type    string `yaml:"type"`
-	BaseURL string `yaml:"base_url"`
-	Token   string `yaml:"token"`
+	Type    string `toml:"type"`
+	BaseURL string `toml:"base_url"`
+	Token   string `toml:"token"`
 }
 
 type ClusterConfig struct {
-	Kubeconfig     string `yaml:"kubeconfig"`
-	Namespace      string `yaml:"namespace"`
-	JobTimeout     int    `yaml:"job_timeout"`
-	MaxConcurrent  int    `yaml:"max_concurrent"`
+	Kubeconfig    string `toml:"kubeconfig"`
+	Namespace     string `toml:"namespace"`
+	JobTimeout    int    `toml:"job_timeout"`
+	MaxConcurrent int    `toml:"max_concurrent"`
 }
 
 type PluginConfig struct {
-	Language string `yaml:"language"`
-	Image    string `yaml:"image"`
+	Language string `toml:"language"`
+	Image    string `toml:"image"`
 }
 
 var envVarRegex = regexp.MustCompile(`\$\{(\w+)\}`)
@@ -52,7 +52,7 @@ func Load(path string) (*Config, error) {
 	expanded := expandEnvVars(string(data))
 
 	var cfg Config
-	if err := yaml.Unmarshal([]byte(expanded), &cfg); err != nil {
+	if _, err := toml.Decode(expanded, &cfg); err != nil {
 		return nil, fmt.Errorf("parsing config: %w", err)
 	}
 

internal/config/config_test.go

@@ -7,20 +7,22 @@ import (
 )
 
 func TestLoad_MissingFile(t *testing.T) {
-	_, err := Load("/nonexistent/config.yaml")
+	_, err := Load("/nonexistent/config.toml")
 	if err == nil {
 		t.Fatal("expected error for missing file")
 	}
 }
 
 func TestLoad_MissingGitToken(t *testing.T) {
-	cfg := `server:
-  addr: ":8080"
-git:
-  type: gitea
-  base_url: "https://git.example.com"
-cluster:
-  namespace: proto-gen`
+	cfg := `[server]
+addr = ":8080"
+
+[git]
+type = "gitea"
+base_url = "https://git.example.com"
+
+[cluster]
+namespace = "proto-gen"`
 	path := writeTempConfig(t, cfg)
 	os.Setenv("GIT_TOKEN", "")
 	_, err := Load(path)
@@ -33,19 +35,22 @@ func TestLoad_ValidConfig(t *testing.T) {
 	os.Setenv("GIT_TOKEN", "test-token")
 	defer os.Unsetenv("GIT_TOKEN")
 
-	cfg := `server:
-  addr: ":9090"
-git:
-  type: gitea
-  base_url: "https://git.example.com"
-  token: ${GIT_TOKEN}
-cluster:
-  namespace: proto-gen
-  job_timeout: 300
-  max_concurrent: 3
-plugins:
-  - language: go
-    image: "proto-gen-go:v1.0"`
+	cfg := `[server]
+addr = ":9090"
+
+[git]
+type = "gitea"
+base_url = "https://git.example.com"
+token = "${GIT_TOKEN}"
+
+[cluster]
+namespace = "proto-gen"
+job_timeout = 300
+max_concurrent = 3
+
+[[plugins]]
+language = "go"
+image = "proto-gen-go:v1.0"`
 	path := writeTempConfig(t, cfg)
 
 	got, err := Load(path)
@@ -73,12 +78,13 @@ func TestLoad_DefaultValues(t *testing.T) {
 	os.Setenv("GIT_TOKEN", "test-token")
 	defer os.Unsetenv("GIT_TOKEN")
 
-	cfg := `git:
-  type: gitea
-  base_url: "https://git.example.com"
-  token: ${GIT_TOKEN}
-cluster:
-  namespace: proto-gen`
+	cfg := `[git]
+type = "gitea"
+base_url = "https://git.example.com"
+token = "${GIT_TOKEN}"
+
+[cluster]
+namespace = "proto-gen"`
 	path := writeTempConfig(t, cfg)
 
 	got, err := Load(path)
@@ -119,7 +125,7 @@ func TestGetPluginByLanguage(t *testing.T) {
 func writeTempConfig(t *testing.T, content string) string {
 	t.Helper()
 	dir := t.TempDir()
-	path := filepath.Join(dir, "config.yaml")
+	path := filepath.Join(dir, "config.toml")
 	if err := os.WriteFile(path, []byte(content), 0644); err != nil {
 		t.Fatalf("writing temp config: %v", err)
 	}