[parent] before attach: child ppid=819
[parent] wrote 'attach' (6 bytes) to /proc/820/ctl
[parent] wrote 'detach' (6 bytes) to /proc/820/ctl
[parent] after detach:  child ppid=819
RESULT: not reproduced -- child ppid after detach is non-zero
waitpid(820)=0 errno=0 (Undefined error: 0)
---- /proc/820/status ----
df0911 820 819 818 818 -1,-1 noflags 1783826743,156619 0,0 0,0 nanslp 1001 1001 1001,1001 -
RUN_EXIT=0

Kernel: DragonFly 6.5-DEVELOPMENT #1: Sun Jul 12 03:17:43 UTC 2026 (single-fix kernel)

Three additional runs all produced:
RESULT: not reproduced -- child ppid after detach is non-zero
waitpid(...)=0 errno=0