pread(fd, buf, 8, -5) [expect EINVAL]      ret=-1 errno=22 (Invalid argument)
pread(fd, buf, 8, INT64_MIN+8)             ret=-1 errno=22 (Invalid argument)
extpread(off=-1, flags=O_FOFFSET)          ret=0 errno=0 (-)
pwrite(fd, "PHANTOM!", 8, -5)              ret=-1 errno=14 (Bad address)
   -> fstat size after phantom pwrite: 20
   -> file content (first 20 bytes): '0123456789ABCDEFGHIJ'
extpwrite(off=-1, flags=O_FAPPEND)         ret=7 errno=0 (-)
   -> fstat size after forced-append: 27
   -> content: '0123456789ABCDEFGHIJAPPEND!'  <-- APPENDED AT EOF
pwrite(fd, 4096B, INT64_MIN) [risky]       ret=-1 errno=27 (File too large)
   -> fstat size after INT64_MIN pwrite: 27
DONE df2731