Summary

• Extract duplicated validation patterns from register_factory_internal() and register_instance_internal() into check_frozen_for_registration() and check_already_registered() helper methods
• Extract duplicated factory exception handling from singleton/transient/scoped resolution branches into invoke_factory_safe() helper method
• Improve maintainability by centralizing error handling logic

Changes Made

New Helper Methods

// Validates container is not frozen before registration
VoidResult check_frozen_for_registration(
    const std::string& type_name,
    interfaces::registry_action action,
    const std::string& error_message) const;

// Validates service is not already registered (caller must hold lock)
VoidResult check_already_registered(
    std::type_index interface_type,
    const std::string& type_name) const;

// Safely invokes factory with exception handling
Result<std::shared_ptr<void>> invoke_factory_safe(
    const std::function<std::shared_ptr<void>(IServiceContainer&)>& factory);

Test Plan

• All 111 existing tests pass
• Build succeeds with no warnings
• Thread safety preserved (double-checked locking pattern intact)
• Audit logging behavior unchanged

Closes #297