transfer of execution with IPC

Sorry if any of these questions are already documented somewhere -- if
so, please refer me to the appropriate documentation.

If I do a send+receive IPC and the receiver is already waiting, does the
receiver immediately run (as opposed to running the scheduler, and
picking a thread that may or may not be the receiver)?

What if it was a send (no receive) IPC?

Assuming neither of these trigger the scheduler, does the scheduler run
again at the end of the original thread's timeslice?

Are these behaviors considered part of the L4 API specification, or are
they implementation details?

Thanks,
Josh