refactor(sdk): simplify provider lifecycle and registration logic

internal/config/config.go

@@ -589,9 +589,6 @@ func LoadConfigOptional(configFile string, optional bool) (*Config, error) {
 		cfg.ErrorLogsMaxFiles = 10
 	}
 
-	// Sync request authentication providers with inline API keys for backwards compatibility.
-	syncInlineAccessProvider(&cfg)
-
 	// Sanitize Gemini API key configuration and migrate legacy entries.
 	cfg.SanitizeGeminiKeys()
 
@@ -825,18 +822,6 @@ func normalizeModelPrefix(prefix string) string {
 	return trimmed
 }
 
-func syncInlineAccessProvider(cfg *Config) {
-	if cfg == nil {
-		return
-	}
-	if len(cfg.APIKeys) == 0 {
-		if provider := cfg.ConfigAPIKeyProvider(); provider != nil && len(provider.APIKeys) > 0 {
-			cfg.APIKeys = append([]string(nil), provider.APIKeys...)
-		}
-	}
-	cfg.Access.Providers = nil
-}
-
 // looksLikeBcrypt returns true if the provided string appears to be a bcrypt hash.
 func looksLikeBcrypt(s string) bool {
 	return len(s) > 4 && (s[:4] == "$2a$" || s[:4] == "$2b$" || s[:4] == "$2y$")
@@ -924,7 +909,7 @@ func hashSecret(secret string) (string, error) {
 // SaveConfigPreserveComments writes the config back to YAML while preserving existing comments
 // and key ordering by loading the original file into a yaml.Node tree and updating values in-place.
 func SaveConfigPreserveComments(configFile string, cfg *Config) error {
-	persistCfg := sanitizeConfigForPersist(cfg)
+	persistCfg := cfg
 	// Load original YAML as a node tree to preserve comments and ordering.
 	data, err := os.ReadFile(configFile)
 	if err != nil {
@@ -992,16 +977,6 @@ func SaveConfigPreserveComments(configFile string, cfg *Config) error {
 	return err
 }
 
-func sanitizeConfigForPersist(cfg *Config) *Config {
-	if cfg == nil {
-		return nil
-	}
-	clone := *cfg
-	clone.SDKConfig = cfg.SDKConfig
-	clone.SDKConfig.Access = AccessConfig{}
-	return &clone
-}
-
 // SaveConfigPreserveCommentsUpdateNestedScalar updates a nested scalar key path like ["a","b"]
 // while preserving comments and positions.
 func SaveConfigPreserveCommentsUpdateNestedScalar(configFile string, path []string, value string) error {