There does not appear to be a reasonable limit on name length

[tranquil sable]

Name character length seems to be limited at 257 characters
This name is
056789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678

[woven mist]

Welcome to your thread, @polar badger
Once you're finished, use /thread archive to close it. If you want to change the thread name, use /thread rename to do so.

[jagged flax]

It seems none of the inputs are limited

they cause the api to error out

[tranquil sable]

Ah yeah

[boreal crane]

not a frontend issue