During the first boot after cfp, the system is under incredibly heavy load due to lots of services performing setup at 
the same time. During this period the launcher starts the cascades and webkit zygotes using posix_spawn. I've found 
about 50% of the time the webkit spawn fails with

Jul 18 20:14:51    3    41   100 launcher: warning spawn_delegate:Could not spawn /bin/webkit-launcher launch delegate, 
err=9(Bad file descriptor)

EBADF isn't a valid return code from posix_spawn according to the main page! (ENOENT is, but that's different...) What 
could cause posix_spawn to return this?

Some differences I can think of between the webkit zygote and the cascades zygote, which hasn't reported this problem, 
are:

webkit is last alphabetically so it is started later; since this error is intermittent, timing could be significant

/bin/webkit-launcher is a symlink to /usr/bin/weblauncher, so spawn is not trying to open the binary directly - could 
EBADF be generated during a failure while trying to follow the symlink? (Note that by the time boot is finished and I 
ssh in, both source and target of the symlink are in place and working fine.)