That's fine if you only ever add, but is likely to fail if you pop FIFO-style. This too is ultimately fixable but means we can no longer assume "every bucket size doubles".

That said, IMO "stable pointers" is overrated; "minimize copying" is all that's useful.

Stable pointers is a limitation for simplicity's sake. If C were better at tracking pointer invalidation, we'd be better at propagating updated pointers.