app.requestSingleInstanceLock on Windows currently (Electron 18.2.3) uses a named pipe to send data (called an acknowledgement) from the first instance back to the second instance. A potential issue with named pipes is that multiple "second instances" might open at the same time, in which case the acknowledgement might not get sent back to the correct second instance in the case that the named pipe name doesn't distinguish between which instance connected. I still have to read up on #34139 and understand how exactly the pipe name is being created, though.

By using message windows, I'm thinking that we can also start up the second instance's message window ahead of time, so that the first instance can directly send back a message, without having to first go through a handshake.

CC @deepak1556