What is Idempotency?

Networks lose responses, not just requests. Your create charge call may have succeeded on the server and died on the way back — retry blindly and you've charged twice. An idempotent operation is safe to repeat: setting a status to paid changes nothing the second time, while appending a row or sending an email does. Where the operation isn't naturally safe, APIs use an idempotency key: a unique id you attach to the request, so the server recognises the repeat and returns the original result instead of doing the work again.

This matters more with agents than with hand-written code, because agents retry on their own judgement. A step that times out, a webhook delivered twice, a loop that re-plans and decides to send again — each is a duplicate waiting to happen, and the model has no way to know the first attempt landed. So idempotency belongs in the connector, not the reasoning. In Velaris the same instinct shows up in tool tiers: the actions where a duplicate would hurt are the write and destructive ones, and destructive calls wait for a human before they fire at all.