Reads a JSON payload a model wrote, fixing the mistakes models commonly make, as the reference SDKs' payload fixer (parse_and_fix) does.

iex> A2UIAgent.PayloadFixer.parse_and_fix(~s({"text": "Hi",}))
{:ok, [%{"text" => "Hi"}]}

Curly quotes are made straight, raw control characters inside strings are accepted, and when the payload does not read, trailing commas before a closing bracket are dropped and it is read again. A single object comes back wrapped in a list.

The direct JSON parser reads blocks with the more forgiving A2UIAgent.DirectJson.JsonReader; this fixer is for code that wants the reference's exact rules.