This is an ignorant question, but, what is the benefit of this if you also have your project open in an editor or IDE (presuming they integrate language server?)

If you're vibe coding without an editor, would this have any benefits to code quality over a test suite and the standard linter for a language?

As part of a bigger refactor, you want to rename some variables. With an LSP hook, the LLM can make the change (more) reliably.

The LLM wants to see the definition of a function. More reliable than grepping.

The same reason you want an LSP in your editor: so you get inline docs and error messages, autocomplete, jump to definition, refactoring actions etc.

Your test suite and linter don't code. They don't help your agent look up definitions of variables, etc.