fix(logging): alias stdlib RotatingFileHandler to concurrent-log-handler (#44873)

hermes_logging.py

@@ -32,10 +32,24 @@
 import os
 import sys
 import threading
-from logging.handlers import RotatingFileHandler
 from pathlib import Path
 from typing import Optional, Sequence
 
+# On Windows, stdlib ``RotatingFileHandler`` calls ``os.rename()`` in
+# ``doRollover()`` and fails with ``PermissionError [WinError 32]`` whenever
+# another process holds an append-mode handle on ``agent.log`` — which is
+# essentially always in Hermes (TUI, gateway, ``hy_memory`` server, MCP
+# servers, and on-demand CLI commands all log from separate processes),
+# pinning ``agent.log`` at the 5 MiB threshold and spamming stderr with
+# a traceback on every emit. ``concurrent-log-handler`` wraps the
+# rename in a cross-process file lock (msvcrt on Windows, fcntl on POSIX)
+# so only one process rotates at a time and the others wait their turn.
+# Drop-in API compatibility — aliasing lets every existing
+# ``RotatingFileHandler`` reference in this module (the class declaration,
+# the ``isinstance`` checks, the docstring) keep working unchanged.
+# See #44873.
+from concurrent_log_handler import ConcurrentRotatingFileHandler as RotatingFileHandler  # noqa: E402
+
 from hermes_constants import get_config_path, get_hermes_home
 
 # Sentinel to track whether setup_logging() has already run.  The function

pyproject.toml

@@ -113,6 +113,19 @@ dependencies = [
   # install rather than gating it behind an extra + a mid-session lazy install
   # (which deadlocked the CLI under prompt_toolkit — see #40490).
   "Pillow==12.2.0",
+  # Windows log rotation. Stdlib ``RotatingFileHandler.doRollover()`` uses
+  # ``os.rename()`` which fails with ``PermissionError [WinError 32]`` on
+  # Windows whenever any other process holds an append-mode handle on
+  # ``agent.log`` (always the case in Hermes — TUI, gateway, ``hy_memory``
+  # server, MCP servers, and on-demand CLI commands all log from separate
+  # processes), pinning ``agent.log`` at the 5 MiB threshold and spamming
+  # stderr on every emit (see #44873). ``concurrent-log-handler`` wraps
+  # the rename in a cross-process file lock (msvcrt on Windows, fcntl on
+  # POSIX) so only one process rotates at a time and the others wait
+  # their turn. Aliasing the import in ``hermes_logging.py`` makes the
+  # swap transparent to every existing ``isinstance`` / class-declaration
+  # check. Pure-Python, no compiled deps.
+  "concurrent-log-handler==0.9.29",
 ]
 
 [project.optional-dependencies]

tests/test_hermes_logging.py

@@ -1,11 +1,14 @@
 """Tests for hermes_logging — centralized logging setup."""
-
+import io
 import logging
 import os
 import stat
 import sys
 import threading
-from logging.handlers import RotatingFileHandler
+# Same alias as hermes_logging.py so the autouse fixture's isinstance
+# checks (which strip rotating handlers between tests) match the new
+# CLH-backed handler class on installs that pulled in #44873's fix.
+from concurrent_log_handler import ConcurrentRotatingFileHandler as RotatingFileHandler
 from pathlib import Path
 from unittest.mock import patch