An HTTP API must reject misspelled JSON fields instead of silently ignoring them. Which d…

An HTTP API must reject misspelled JSON fields instead of silently ignoring them. Which decoder setup enforces that contract?

1. Create a `json.Decoder`, call `DisallowUnknownFields`, then decode.
2. Use `json.Unmarshal`; it rejects unknown fields by default.
3. Add `omitempty` to every response field.