Streaming JSON Parsers: The Gap Between Tokens and Typed Objects
The model is emitting JSON token by token. Your UI wants to render fields the moment they materialize — a confidence score before the long answer body, the arguments of a tool call as the model fills them in. Then someone wires up JSON.parse on every chunk and the whole thing falls over, because JSON.parse is all-or-nothing. It needs a balanced document to return anything. Until the model emits the closing brace, you have nothing to show.
This is not a parser problem you can fix with a try/catch. The standard JSON parser was designed against a content-length-known HTTP response. Partial input is not a state it models — it is "input error." When you treat a token stream as if it were an HTTP body, you inherit thirty years of "the document is either complete or invalid," and your UI pays the bill.
