fix(logs): delete and download only rotated copies under one rule

Rule R (#329): a file is a rotated copy only when it is a direct entry of
the log folder named prompt_manager.log.<n> (n >= 1, no leading zero,
compared after normcase) and a regular file that is not a symlink or a
junction. Everything else is never deleted.

- Clear (POST /logs/truncate) empties the active log and deletes only
  rotated copies; a .bak, a .1.gz, any other file and every link are kept.
  It runs off the event loop under one files lock and the file handler's
  lock, so no rollover renames a file mid-way, and logs only afterwards.
- delete_rotated(expected) deletes exactly the reviewed copies, or nothing
  when one of them changed (size, mtime_ns, inode, missing, now a link).
- The download serves only a listed regular, non-link file, opened without
  following links and read off the loop; a link or folder is a 404.
- /logs/files rows gain kind; files and stats read links with lstat and
  stats no longer count a link's target.
- The config update runs off the loop and swaps handlers under the files
  lock.

py/api/logging_routes.py

@@ -1,6 +1,13 @@
-"""Logging API routes for PromptManager."""
+"""Logging API routes for PromptManager.
+
+Every route that names a log file goes through Rule R (#329,
+``utils/logging_config.py``): a download is served only for a regular,
+non-link file listed directly in the log folder, and Clear deletes only
+rotated copies. File work runs off the event loop.
+"""
 
 import os
+import stat
 
 from aiohttp import web
 
@@ -85,6 +92,31 @@ def _validate_log_config(data):
     return clean, None
 
 
+def _read_log_bytes(path):
+    """The whole file at ``path``, opened without following a link (blocking).
+
+    The file is checked again through the open handle (a regular file), so a
+    name swapped for a link after it was listed is refused as missing. The
+    handle is closed before this returns.
+    """
+    flags = os.O_RDONLY | getattr(os, "O_BINARY", 0) | getattr(os, "O_NOFOLLOW", 0)
+    try:
+        fd = os.open(str(path), flags)
+    except OSError as error:
+        if getattr(os, "O_NOFOLLOW", 0) and os.path.islink(str(path)):
+            raise FileNotFoundError("Log file not found") from error
+        raise
+    with os.fdopen(fd, "rb") as handle:
+        if not stat.S_ISREG(os.fstat(handle.fileno()).st_mode):
+            raise FileNotFoundError("Log file not found")
+        return handle.read()
+
+
+def _download(logger_manager, filename):
+    """``bytes`` of a downloadable log file; FileNotFoundError otherwise."""
+    return _read_log_bytes(logger_manager.log_file_entry(filename))
+
+
 class LoggingRoutesMixin:
     """Mixin providing logging-related API endpoints."""
 
@@ -195,16 +227,16 @@ class LoggingRoutesMixin:
                     {"success": False, "error": "Invalid filename"}, status=400
                 )
 
-            log_file_path = logger_manager.log_dir / filename
-
-            if not log_file_path.exists():
+            try:
+                file_content = await self._run_in_executor(
+                    _download, logger_manager, filename
+                )
+            except FileNotFoundError:
+                # Missing, a link, a folder or not listed: all read as absent.
                 return web.json_response(
                     {"success": False, "error": "Log file not found"}, status=404
                 )
 
-            with open(log_file_path, "rb") as f:
-                file_content = f.read()
-
             return web.Response(
                 body=file_content,
                 content_type="text/plain",
@@ -224,7 +256,7 @@ class LoggingRoutesMixin:
         """Truncate all log files."""
         try:
             logger_manager = self._get_logger_manager()
-            results = logger_manager.truncate_logs()
+            results = await self._run_in_executor(logger_manager.truncate_logs)
 
             return web.json_response(
                 {
@@ -266,7 +298,7 @@ class LoggingRoutesMixin:
                 return web.json_response({"success": False, "error": error}, status=400)
 
             logger_manager = self._get_logger_manager()
-            logger_manager.update_config(clean)
+            await self._run_in_executor(logger_manager.update_config, clean)
 
             return web.json_response(
                 {