Short answer: iA Writer tells you what the AI wrote. Stet asks you first.
iA Writer took AI authorship seriously before almost anyone. Its Authorship feature marks where your text came from: your own words stay solid, pasted AI text is dimmed. It works locally, sends nothing to a server, and it shaped how a lot of people think about writing with AI. We count it as an inspiration, and it shows in Stet's design.
Authorship is a receipt. The AI text is already in your document. It's tinted, and that's honest, but it landed without a decision from you.
That model fits how iA Writer expects you to work: you talk to the AI somewhere else and paste the result in. It doesn't fit how agents work now. An agent with access to your files doesn't paste. It edits, directly, sometimes while you're doing something else. Paste detection can't see that.
Stet watches the files themselves. When an agent changes a document, the change arrives as a proposal, not as new text in your draft. You see exactly what moved, and you accept, reject, or refine it. The document only ever contains what you approved, and the record of each decision stays with the file.
Attribution is the receipt. Review is the decision. Stet is built around the decision.
If you write mostly on your own and paste the occasional AI passage, iA Writer's approach may be all you need. The moment agents start editing your files for you, you need a gate, not a tint.
Part of Where Stet fits, the map of the markdown neighborhood.