The Steam client only sets critical environment variables for the game
process itself, not for getcompatpath etc. This verb lets the Steam
client wait for the prefix to shut down so it can restart the prefix
with the variables set.
Required to avoid duplicate controllers when controller config support
is enabled, for example.
Steam cloud sync places save files into pfx/ before proton is ever
invoked. Previously we would assume the prefix is valid if pfx/ exists
and run wine, which lead to very broken prefixes. Instead we should
check for files that cloud sync will never create (user.reg) and merge
the default prefix into any existing prefix tree.
DXVK needs to make some calls to openvr_api, but the game may not ship
it in a predictable location. So we provide a fallback called
openvr_api_dxvk.dll, which DXVK knows to load.
Andrew Eikum
Seppo Yli-Olli