Reads a parameter the way the app does: the value the process fixed for the
parameter's config at its first read, else the kept values now (and fixes
them for the rest of the process), and the app's default when no answer sent
a value. A user parameter of a process with no signed-in account reads its
default (no user config exists then). A declaration that disagrees with its
specifier dies with MobileConfigParamDeclarationError.
Reads a parameter the way the app does: the value the process fixed for the parameter's config at its first read, else the kept values now (and fixes them for the rest of the process), and the app's default when no answer sent a value. A user parameter of a process with no signed-in account reads its default (no user config exists then). A declaration that disagrees with its specifier dies with MobileConfigParamDeclarationError.