Keep the iovec buffers alive until the kernel reads them - #13
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The iovec builders cast unreferenced temporaries to void pointers and the array construction in Jiov.struct copies structures without their keepalives, so the kernel could read freed memory whenever the allocator reused those blocks before jail_set(2). Keys and values now retain their backing buffers, invalidated when a value is reassigned, and every iov_base points at owned memory through ctypes.addressof. The errmsg pair keeps its key buffer on the Jiov and no longer takes the buffer address through an ill-typed POINTER(c_char_p) construction.
The unit test rebuilds every entry of the iovec array from its raw addresses after provoking allocator reuse. The integration test creates a jail under the same conditions and resolves it by name through jail_get(2).
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Building a Jiov cast unreferenced temporaries to void pointers, so jail_set(2) could hand the kernel addresses of memory that Python had already freed - it worked by allocator luck.