THE SHORT ANSWER
Anything the agent says in your name that is not a purchase. Stripe's protection for purchases made through Link's wallet for agents covers accidental damage, lost items, price drops, no-fee returns, and return guarantees, which are all losses with a price and a reversal path. The Muse agent Simon Willison quoted on September 28, 2026 told a waiting visitor "Yep I'm here!" when nobody was home and earned its user a negative rating; no money moved, so nothing applies. Sort agent actions into three classes: refundable, which you insure; bounded, which you budget or gate with approval; and said in someone's name, which you verify or do not send. My own expense agent cost about $2,400, and the trust took a quarter to rebuild.
Stripe insured the agent's purchase in the same week a Muse agent's mistake turned out to be a sentence, and Nothing Refunds a Sentence is about the class of agent action that sits outside both insurance and budgets. The two bills behind the argument, an expense agent that cost about $2,400 and a quarter of trust, and an onboarding agent that was correct and lowered activation, are in 10 AI Agents I Built That Failed. The Honest Retrospective. The inward-facing version of the same rule, where the agent's claims about its own work are checked against receipts, is The Receipt Gate.
It belongs to the Enterprise AI Agents argument: what each successful outcome costs includes the costs that never reach an invoice.