[aassddffasdf]

You would still have to ensure balancing somehow. Both "]" and "}" are valid "closing brackets" and the correct one to choose is context-dependent.

[gyy52380]

You can determine which brackets you need in which order by parsing the incomplete json which was generated so far.

[dontreact]

That won't do it, also need to close other stuf

{"this": "is valid json so farrrrrrrrrrrrrr

But yeah the general idea makes sense. Once you hit a timeout, change the mask to things that will close existing open things in a valid manner (}, ), ], ")