Out of heap space crash

After roughly a 24-48 hours it will always crash with a javascript out of heap space error (memory leak). This is with one cabal open (the default one) and not much activity.

It's been happening for the last few versions (at least). Fixing this ought to be the top priority, even if it's something in an upstream library.

No file, test, or entry point is named. Start by reproducing the crash with one default cabal open and little activity, then use JavaScript heap diagnostics to identify the leak; done means the client no longer reaches an out-of-heap crash after 24–48 hours.

Written by the indexing model from the issue text.