What is the Command pattern and command bus in PHP?

The Command pattern encapsulates a request as a standalone object containing all the information needed to perform the action. This allows parameterizing clients with different requests, queuing or logging requests, and supporting undo operations. In PHP, a command is a simple DTO: class CreateUserCommand { public function __construct(public readonly string $name, public readonly string $email) {} }. A Command Bus routes commands to their handlers: $bus->dispatch(new CreateUserCommand("Alice", "alice@example.com")) finds and calls the corresponding CreateUserHandler::handle(). This decouples the caller from the handler, makes operations testable in isolation, enables middleware (logging, transactions, authorization) around any command, and supports async execution by pushing commands onto a queue. Libraries like Tactician provide a simple command bus, while Laravel's Job system implements a variant of this pattern.