feat(resilience): Robust Cross-Platform Process-Tree Orphan Sweeper

[sdageltc]

Summary & Motivation

Worker adapters frequently spawn external tool processes, compilers, test runners (pytest, npm test, cargo build), or language servers. If a contract times out or is aborted via Ctrl+C / SIGINT, child and grandchild processes can detach and become runaway orphans consuming 100% CPU in the background.

While orchestrator/verifier.py contains basic process termination, we need a unified, resilient Cross-Platform Process-Tree Orphan Sweeper across all worker adapters.

---

Proposed Solution

1. Unified Process Tracker (orchestrator/process_guard.py):
   • Windows: Uses Job Objects (CreateJobObject, AssignProcessToJobObject) with JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE. When the parent handle closes, Windows OS kernel automatically terminates all descendants atomically.
   • POSIX (macOS / Linux): Uses process group leadership (os.setpgrp() / preexec_fn=os.setsid) paired with os.killpg(pgid, signal.SIGKILL).
2. Signal Trap & Cleanup Registry:
   • Maintains an in-memory process registry.
   • Registers atexit and signal.signal handlers (SIGINT, SIGTERM, SIGHUP) to execute immediate sweep before exit.

---

Acceptance Criteria

• Grandchild subprocesses spawned by workers or test runners are guaranteed terminated on timeout.
• Pressing Ctrl+C during a running loop terminates all spawned subprocesses immediately with 0 orphan processes left behind.
• Tested on macOS (Darwin), Linux, and Windows.