Interactive Haskell + folding plugins

Hmm, every now and then I'm hitting this error. I don't know why it comes up exactly, and peeking at the _haskell-process-log_ the haskell process is still doing expected things AFAICT. If anybody wants to help walk me through debugging this, let me know.

Reproduce the intermittent error involving Interactive Haskell and folding plugins, then inspect haskell-process-log while the Haskell process continues. Start by capturing the exact error and the plugin or configuration that triggers it; done means identifying the cause and documenting or fixing the failure with a reproducible check.

Written by the indexing model from the issue text.