fix(config): align yaml path validation

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

config.go

@@ -106,6 +106,9 @@ func configTypeForPath(path string) (string, error) {
 	if ext == "" && filepath.Base(path) == ".env" {
 		return "env", nil
 	}
+	if ext == "" {
+		return "yaml", nil
+	}
 
 	switch ext {
 	case ".yaml", ".yml":
@@ -236,6 +239,13 @@ 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, coreerr.E("config.Load", "failed to read config file: "+path, err)

config_test.go

@@ -239,6 +239,15 @@ 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: [[[["
@@ -261,6 +270,19 @@ func TestConfig_LoadFile_JSON_Good(t *testing.T) {
 	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"
@@ -312,6 +334,17 @@ 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()