== TEST 1: RLIMIT_FSIZE vs O_APPEND ==
prefill: size=2097152
rlimit_fsize = 1MiB, file already 2MiB
append-write(4096): ret=-1 errno=27 sigxfsz=1 size=2097152
  -> OK: EFBIG (limit enforced)
append-write after lseek(0): ret=-1 errno=27 sigxfsz=1 size=2097152
control plain-write@2MiB: ret=-1 errno=27 sigxfsz=1
  -> OK: limit enforced for non-append
== TEST 2: chflags UF_APPEND (append-only) enforcement ==
(fd opened BEFORE the flag is set; kernel open-gate cannot
 retroactively apply O_APPEND to an existing descriptor)
chflags(UF_APPEND) ok (file held open rw since before)
pwrite@0 on uappnd via pre-opened fd: ret=-1 errno=1
  -> OK: EPERM
write@4 on uappnd: ret=-1 errno=1
content now: [AAAABBBBCCCC] (12 bytes)
  -> OK: content untouched