Fix process-group kill test to work without an init process

os.kill(pid, 0) succeeds on a zombie, and a killed orphan stays a
zombie until reaped — which never happens inside a CI container with
no init. The test read that as "still alive" and failed there while
passing locally. It now reads the process state from /proc, with a
control assertion so a broken liveness check cannot pass silently.
The group kill itself was correct.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

nisse-dev/tests/test_tools.py

@@ -77,6 +77,18 @@ def test_command_timeout_is_reported(tmp_path: Path) -> None:
     assert "timed out" in outcome.result
 
 
+def _is_running(pid: int) -> bool:
+    """os.kill(pid, 0) is not enough: a killed orphan stays a zombie until
+    something reaps it, and no init does that inside a CI container. Read the
+    process state instead."""
+    try:
+        stat = Path(f"/proc/{pid}/stat").read_text()
+    except FileNotFoundError:
+        return False
+    # State is the first field after the parenthesised comm.
+    return stat.rsplit(")", 1)[1].split()[0] != "Z"
+
+
 def test_timeout_kills_the_whole_process_group(tmp_path: Path) -> None:
     ws = Workspace(tmp_path / "work", timeout_s=1)
     pidfile = ws.root / "child.pid"
@@ -84,8 +96,8 @@ def test_timeout_kills_the_whole_process_group(tmp_path: Path) -> None:
     ws.run_command(f"(sleep 30 & echo $! > {pidfile}); sleep 30")
     assert pidfile.exists()
     pid = int(pidfile.read_text().strip())
-    with pytest.raises(ProcessLookupError):
-        os.kill(pid, 0)
+    assert _is_running(os.getpid()), "liveness check is broken, not the kill"
+    assert not _is_running(pid)
 
 
 def test_agent_credentials_are_not_inherited(