The Guardian is a deterministic validation layer that runs on every change submitted through Site Manager. It is plain code with no AI API cost and no processing delay. It runs instantly.
What it checks: whether the change targets a tagged content slot (not structure), whether the new value is valid for the field type, whether the result would leave a section empty, and whether the rendered output would break the layout. If any check fails, the change is rejected with an explanation. Nothing gets through that hasn't passed every test.
This is why clients who have never used a CMS can use Site Manager on day one. The risky parts of the site are outside the editor's reach by design.