On Windows the descendant tree used to reap a cancelled bash run is
built from raw th32ParentProcessID links that outlive their recorded
parent. A recycled pid matching the harness's stale parent pid could
surface omp itself (or an ancestor) as a false descendant, and
signal_tree TerminateProcess'd it — killing the session with no
cleanup and no session_exit record when a blocking command hit its
timeout.
Add host_protected_pids() (harness pid plus its resolvable ancestor
chain) and skip those pids in signal_tree and terminate_tree. The
guard is cross-platform: a no-op on Unix, where the descendant walk is
already identity-pinned, and the safety net that keeps a tool timeout
from ever taking down the harness on Windows.
Fixes#7452
roboomp
25633d357d