fix(serve): only "no such process" from ps means the Desktop parent is gone

The stderr sniff also matched "not found", which BSD ps prints for an
unsupported column ("ps: lstart: keyword not found", rc=1, verified on
macOS). That would have classified a healthy parent as dead and os._exit'd
the backend — the fail-unsafe direction the watchdog must never take. Keep
the explicit missing-process message only; the macos_only test now pins the
"keyword not found" case as a plain OSError. The standalone
ProcessLookupError test (already green on main) folds into the degrade test.

hermes_cli/web_server_lifecycle.py

@@ -75,10 +75,10 @@ def _process_start_marker(pid: int) -> str:
     marker = result.stdout.strip()
     if result.returncode == 0 and marker:
         return f"ps:{marker}"
-    stderr_lower = result.stderr.lower()
-    if (result.returncode == 1 and not marker) or any(
-        msg in stderr_lower for msg in ("no such process", "not found")
-    ):
+    # rc==1 with empty output is the portable "no such pid"; "No such process" widens that for ps
+    # builds that say so explicitly. Any other failure stays an OSError so the watchdog degrades to
+    # pid liveness instead of exiting on a healthy backend.
+    if (result.returncode == 1 and not marker) or "no such process" in result.stderr.lower():
         raise ProcessLookupError(pid)
     raise OSError(f"ps could not inspect PID {pid}: {result.stderr.strip()}")
 

tests/hermes_cli/test_serve_parent_watchdog.py

@@ -191,22 +191,19 @@ def test_parent_watchdog_degrades_to_pid_liveness_when_marker_probe_raises_oserr
     assert _is_serve_orphaned(4242, marker, pid_exists=lambda _pid: True,
                               process_start_marker=broken_marker_probe) is False
 
-
-def test_parent_watchdog_detects_dead_parent_on_process_lookup_error():
-    """#80204: ``ProcessLookupError`` from the marker probe means the parent is gone, whatever
-    a (possibly recycled) pid liveness check says."""
     def lookup_error_probe(pid: int) -> str:
         raise ProcessLookupError(pid)
 
-    assert _is_serve_orphaned(4242, "ps:Thu Aug 20 22:33:11 2026", pid_exists=lambda _pid: True,
+    # ProcessLookupError is conclusive on its own, whatever a recycled-pid liveness check says.
+    assert _is_serve_orphaned(4242, marker, pid_exists=lambda _pid: True,
                               process_start_marker=lookup_error_probe) is True
 
 
 @pytest.mark.macos_only
 def test_ps_marker_probe_classifies_missing_process_vs_other_ps_failures(monkeypatch):
-    """The darwin ``ps`` probe raises ``ProcessLookupError`` only for a missing-process message;
-    any other non-zero exit stays a plain ``OSError`` so the watchdog degrades instead of killing
-    a healthy backend."""
+    """The darwin ``ps`` probe raises ``ProcessLookupError`` only for an explicit missing-process
+    message; any other unknown failure stays a plain ``OSError`` so the watchdog degrades instead
+    of killing a healthy backend."""
     import subprocess
 
     from hermes_cli import web_server_lifecycle