Working in Xcode as usual, suddenly the entire display goes white.
I have a second monitor hooked up for non-Xcode things, so I managed to fish the System Preferences window out of the iMac display and into the secondary one and move the menu bar over. It runs normally, as far as I can tell, there's just a not-working built-in display.
Zapping PRAM does nothing. Safe Mode does nothing.
Possibly relevant -
rsync was locking up repeatedly. It would come across certain items (mostly related to Spotlight) and completely freeze.
Kept it going for a while with
[^C ; sudo rm -rf … ; rsync …] but then the external drive stopped showing up in Finder. Still visible in Disk Utility.
Bad monitor? It's not off/black, so that probably isn't it.
Failing HD? Disk Utility isn't complaining about anything.
Bad display driver? How can I find and fix it?
Bad graphics card? Is there a cheaper way to test that than buying a replacement?