The stdio-MCP orphan reaper (`_kill_orphaned_mcp_children`) and the local
environment's `_kill_process` both signalled a process *group* via
`os.killpg(pgid, sig)` using a PGID captured at spawn time. Once the original
child exits and is reaped, the kernel can recycle that PID/PGID onto an
unrelated process group, so a later sweep would `killpg` a stranger.
Observed in the wild: a long-running gateway reaped a recycled PGID that had
landed on a desktop browser's session leader, SIGTERM-ing Firefox at irregular
intervals (proven with the kernel `signal:signal_generate` tracepoint —
`comm=firefox` killed by the hermes gateway via a recycled group id).
Fix: record each leader's start time (`/proc/<pid>/stat` field 22, via the
existing `gateway.status.get_process_start_time`) alongside the PGID, and
re-check it before signalling. A PGID whose leader's start time no longer
matches — or whose leader is gone — is never signalled. When no start time is
available (e.g. macOS has no /proc) the guard degrades to the prior best-effort
behaviour, so non-Linux platforms are unaffected.
Adds regression tests covering both the recycled-PID (skip) and matching-PID
(signal) paths.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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