how does "strictly nonoverlapping process groups" work if processes need to share data ex post facto? simple! for two processes A and B, their respective supervisor processes S_A and S_Bmust both request a resource that exposes an interface to write data outside the process-local i/o space. this comes in the form of a capability, and it's the exact definition of our "named i/o sync domains"!
and alternatively but no less appropriately, we will still allow supervisors to request a shared memory buffer capability from the kernel, which it can then expose to multiple processes in its IPC graph. unlike the highly-optimized filesystem abstraction i'm providing (which adds on the concept of "i/o transactions" to negotiate the communication of data across supervisor trees in a structured way), shared memory is going to rely upon the semantics described by the C11 weak memory model for atomic operations for consistency.
the point here is absolutely not to nag applications to do "safe" i/o--all of this is purely motivated by my personal need for speed!!!!