FireCloud -- hard to understand failure (parameter.name too long)

My FC method is failing with an inscrutable error:

Invalid value for field "parameter.name": too long: 132 bytes, want no longer than 128 bytes

Is this 128 byte limit something universal that I'm bumping up against? I don't know what parameter might be overflowing. Hard to understand this error. None of stdout, stderr, nor JES logs were written to/delocalized, so it seems like the error is happening from the very start.

Thanks for any advice,

Eric