Yes, you can make a memory leak when targetting C, C++ and Swift. Same as when you code in C, C++ and Swift directly.
So you can (and probably should) do almost any memory management as you would in C++. Except I don't see any alternative for `weak_ptr` at the moment.
Well that's already out the door because I almost never use shared_ptr in C++ code. The C++ core guidelines recommend using unique_ptr whenever possible. If you're going to use shared_ptr literally everywhere you do dynamic allocation, you'd be better off using a tracing GC to avoid the extra pointer indirection (and cache miss) with every dereference.
It seems to me that Cito should have manual memory management because a manual memory language can be trivially mapped onto a GC language (just turn every free or delete to an nop), while the inverse problem is intractable in the general case.
A shared_ptr can be optimized to unique_ptr if it's not copied.
Not sure what you mean by "a GC language". Most cito targets are garbage-collected.