fix(kanban): detect darwin zombie workers (salvages #20023)

hermes_cli/kanban_db.py

@@ -76,6 +76,7 @@
 import re
 import secrets
 import sqlite3
+import subprocess
 import sys
 import time
 from dataclasses import dataclass, field
@@ -2141,16 +2142,16 @@ def _pid_alive(pid: Optional[int]) -> bool:
     Cross-platform: uses ``os.kill(pid, 0)`` on POSIX and ``OpenProcess``
     on Windows. Returns False for falsy PIDs or on any OS error.
 
-    **Zombie handling (Linux):** ``os.kill(pid, 0)`` succeeds against
+    **Zombie handling:** ``os.kill(pid, 0)`` succeeds against
     zombie processes (post-exit, pre-reap) because the process table
     entry still exists. A worker that exits without being reaped by its
     parent would stay "alive" to the dispatcher forever. Dispatcher
     workers are started via ``start_new_session=True`` + intentional
     Popen handle abandonment, so init reaps them quickly — but during
     the window between exit and reap, we'd otherwise see stale "alive"
-    signals. On Linux we additionally peek at ``/proc/<pid>/status``
-    and treat ``State: Z`` as dead. On other POSIX or on Windows the
-    zombie check is a no-op.
+    signals. On Linux we peek at ``/proc/<pid>/status`` and treat
+    ``State: Z`` as dead. On macOS we ask ``ps`` for the BSD ``stat``
+    field and treat values containing ``Z`` as dead.
     """
     if not pid or pid <= 0:
         return False
@@ -2164,7 +2165,8 @@ def _pid_alive(pid: Optional[int]) -> bool:
         return True
     except OSError:
         return False
-    # Still here → kill(0) succeeded. Check for zombie on Linux.
+    # Still here → kill(0) succeeded. Check for zombie on platforms
+    # where we have a cheap, deterministic process-state probe.
     if sys.platform == "linux":
         try:
             with open(f"/proc/{int(pid)}/status", "r") as f:
@@ -2179,6 +2181,23 @@ def _pid_alive(pid: Optional[int]) -> bool:
             # PermissionError shouldn't happen for our own children but
             # be defensive.
             pass
+    elif sys.platform == "darwin":
+        try:
+            proc = subprocess.run(
+                ["ps", "-o", "stat=", "-p", str(int(pid))],
+                stdout=subprocess.PIPE,
+                stderr=subprocess.DEVNULL,
+                text=True,
+                timeout=1,
+                check=False,
+            )
+            if proc.returncode != 0:
+                return False
+            if "Z" in (proc.stdout or "").strip():
+                return False
+        except (OSError, subprocess.SubprocessError, TimeoutError):
+            # If the secondary probe fails, keep the kill(0) answer.
+            pass
     return True
 
 

tests/hermes_cli/test_kanban_core_functionality.py

@@ -13,9 +13,11 @@
 import argparse
 import json
 import os
+import subprocess
 import threading
 import time
 from pathlib import Path
+from types import SimpleNamespace
 from typing import Optional
 
 import pytest
@@ -183,6 +185,20 @@ def test_pid_alive_helper():
     assert not kb._pid_alive(2 ** 30)
 
 
+def test_pid_alive_detects_darwin_zombie(monkeypatch):
+    monkeypatch.setattr(kb.sys, "platform", "darwin")
+    monkeypatch.setattr(kb.os, "kill", lambda pid, sig: None)
+
+    def fake_run(args, **kwargs):
+        assert args == ["ps", "-o", "stat=", "-p", "123"]
+        assert kwargs["stdout"] is subprocess.PIPE
+        return SimpleNamespace(returncode=0, stdout="Z+\n")
+
+    monkeypatch.setattr(kb.subprocess, "run", fake_run)
+
+    assert kb._pid_alive(123) is False
+
+
 def test_detect_crashed_workers_reclaims(kanban_home):
     """A running task whose pid vanished gets dropped to ready with a
     ``crashed`` event, independent of the claim TTL."""