You might find on closer inspection that at least some of those ad_proc defs are for procs that are submitted to ad_sched*. I might be wrong but it seems a logical guess. In this case only the thread doing the *-init.tcl needs to see the proc def.
I think your idea to go back to only sourcing these files once upon startup rather than for each thread is the right thing to do. Folks with their own custom packages won't have to rewrite them, etc etc.
Thanks for all the work you've done to get all this straightened out, BTW! The new system of callbacks is really great.
