[zokier]

> Conceptually, you think of "spawning a child" as something that is in some kind of container (the parent process), but the underlying mechanics are not like this at all,

That is not quite right either, the newly created child processes generally go to the same process group as the parent, the process groups (and sessions) forming those "containers".

Tbh this is one of the many murky areas of UNIX.

[CGamesPlay]

My explanation definitely glosses over some details, but a process group isn't really a "container" in any meaningful sense, either. It can be left by any member (who can form a new process group completely unrelated to its old one, setsid), which resets the "controlling terminal" but isn't related to the standard output channels at all.