docs(infra): IR-150 sample 9, file IR-155 (long_child leaks PING.EXE)

IR-150 sample 9: hertz's W7 order-check reap on kitsubito. Forced zero
(202 @ nlink 2), gap 0 B, write census taken in a separate call before
launch. The zeros now read forced 7, unforced 1, vacuous 1.

IR-155: on Windows, brainproc's long_child() is cmd /C ping, and the
supervisor's kill hits cmd while the PING.EXE grandchild keeps
nextest's inherited stderr open for about 29 s, reported as LEAK.
Proven with a PowerShell probe. W7 is exonerated by hunk. Base
behaviour is INFERRED, not measured. Fix: spawn ping directly and null
its stderr and stdin.

Co-authored by: hertz
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KR5QdzrHXYGL1djRTBNKEG