Hooks are meant to be 'deterministic' because they are only used for executing scripts on a specific step. So, for instance, you can execute your lint on PostEd

Hooks are meant to be 'deterministic' because they are only used for executing scripts on a specific step. So, for instance, you can execute your lint on PostEdit so every time it edits a file in your project, the harness runs your linter. With that said, part of hooks is you can return a json object to the agent which gives it instructions such as stop, continue, etc but those to my understanding are all very explicit constants rather than loosey-goosey prompts you can pass it. If this person looked into hooks more, they could write a script that would run their project's tests and then tell Claude to stop if tests end via a non-0 exit code.