Source: AWS Builders' Library, "Making retries safe with idempotent APIs" by Malcolm Featonby. https://aws.amazon.com/builders-library/making-retries-safe-with-idempotent-APIs/
Locator: section "Reducing client complexity with idempotent API design."
Quoted: "We can significantly simplify client code by delivering a contract that allows the client to make a simplifying assumption that any error that isn't a validation error can be overcome by retrying the request until it succeeds." And: "You could derive a hash of the parameters present and assume that any request from the same caller with identical parameters is a duplicate. On the surface, this seems to simplify both the customer experience and the service implementation. However, we have found that this approach doesn't work in all cases."
What this establishes: idempotency requires an explicit caller-supplied token, not a parameter hash. Two calls with identical parameters can be two distinct intents (the article's example: launching…