MettleM0111Borrowed pointer invalidated by realloc
Reported by the compiler as an error or warning.
mettle explain M0111A pointer into a heap buffer is used after the buffer was passed to realloc. realloc may move the allocation, leaving every old interior pointer dangling - even when the call "usually" grows in place.
Fix: recompute interior pointers from the (new) base pointer after every realloc.