test(hooks): pin bare pkill — the ablation found the pidscoped gate unpinned

Second ablation leg: replacing check_pkill's `[ "$pidscoped" -eq 1 ] && return 0`
with an unconditional allow left the self-test green at 68/0. Bare `pkill` is
the only input that reaches that gate — every other spelling returns earlier —
so the branch had no case standing on it. It does now.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01P58euzUXCVJNwmhuPC9DXY

Author: claude

.claude/hooks/guard-process-kill.selftest.sh

@@ -84,6 +84,11 @@ expect block 'pkill --signal TERM node'
 expect block 'pkill -f "pnpm --filter @objectstack/spec test"'
 expect block '/usr/bin/pkill -f vitest'
 expect block 'OS_FOO=1 pkill -f vitest'
+# Bare `pkill` — its option loop completes with no PID-family selector, and it is the ONLY
+# input that reaches the pidscoped gate at the end of check_pkill. Without this row that gate
+# is unpinned: an ablation replacing it with an unconditional allow left this file green at
+# 68/0, which is how the hole was found rather than shipped.
+expect block 'pkill'
 
 echo "== killall is the spelling a pkill-only rule would go silent on =="
 expect block 'killall node'