S00-014: Make successful runner process-tree cleanup idempotent

Changes: Record completed termination on the Popen instance after all cleanup steps succeed; avoid repeated signals to the reaped group. Add deterministic repeated-EPERM and failed-descendant-kill retry regressions without suppressing permission errors.
Validation: Four focused cleanup tests passed; make check passed 72 tests and plan/snapshot validation. git diff --check passed. Natural prior EPERM did not recur; injected EPERM reproduced the pre-fix failure. No application or parent-task acceptance is claimed.

Task: S00-014
Agent: auto-ci-cd-14343249da62
Role: ci-cd
Action: claim
Status: review

Task title: Fix repeated runner cleanup after a submitted parent is reaped

planning/task_matrix.csv

@@ -11,7 +11,7 @@ S00-009,S00,orchestrator,security,todo,,"S00-003, S00-004, S00-005, S00-006, S00
 S00-011,S00,ci-cd,security,done,auto-ci-cd-d105e8027730,S00-001,Restore verified npm registry access for the stack spike
 S00-012,S00,ci-cd,qa,blocked,auto-ci-cd-28868645424b,"S00-001, S00-011, S00-013, S00-014",Fix runner prompt delivery after partial stdin timeout
 S00-013,S00,ci-cd,qa,done,auto-ci-cd-5f68f03dd33b,"S00-001, S00-011",Bound oversized S21-006 runner context without truncating requirements
-S00-014,S00,ci-cd,qa,todo,,"S00-001, S00-011, S00-013",Fix repeated runner cleanup after a submitted parent is reaped
+S00-014,S00,ci-cd,qa,review,auto-ci-cd-14343249da62,"S00-001, S00-011, S00-013",Fix repeated runner cleanup after a submitted parent is reaped
 S00-010,S00,qa,orchestrator,todo,,"S00-001, S00-002, S00-003, S00-004, S00-005, S00-006, S00-007, S00-008, S00-009",Gate: Профиль и проверка стека
 S01-001,S01,orchestrator,security,todo,,S00-010,Описать identity/model contracts
 S01-002,S01,orchestrator,security,todo,,"S00-010, S01-001",Описать async account context