I don't see that race condition as too critical because the same can happen everywhere where PIDs are recycled too soon. If we find out that PIDs get recycled far too quickly, we can think of a solution then. :)

A pipe cannot exist at process startup (by mechanism), because every process creates \\.\pipe\Perl\$$ and $$ is unique per process. The fork() emulation and signals between fork()ed children will be interesting to solve under this umbrella, but signals beween forked children could be handled by using shared memory anyway. I'm not sure how unique the fork-child-PIDs are across process boundaries, so maybe using $$ would still work, even with the fork emulation.