Websockets can't tell whether a connection was closed cleanly

[tehdragonfly]

A regular disconnect message should be sent under the following circumstances:

• The user disconnects via the "Abscond" button
• The user navigates to a different page in the same tab
• The user closes the tab

A connection error message should be sent under the following circumstances:

• The user's browser crashes
• Nginx times out the socket

So far I haven't been able to reliably distinguish between these two sets of circumstances.

[tehdragonfly]

Some test results (in Firefox):

• Disconnected via abscond button: no close code.
• Typed /search into the URL bar: close code 1001.
• Closed the tab: close code 1001.
• Commented out ping code so nginx timed out: no close code.
• killall -9 firefox: no close code.
• killall -9 nginx: no close code.