fix timezone handling and logging fallback robustness

src/vlm/logging_config.py

@@ -13,13 +13,16 @@ from pathlib import Path
 from typing import Optional
 
 
-# Default log directory
-DEFAULT_LOG_DIR = Path.home() / ".vlm" / "logs"
 DEFAULT_LOG_FILE = "vlm.log"
 MAX_LOG_SIZE = 10 * 1024 * 1024  # 10MB in bytes
 BACKUP_COUNT = 5  # Keep 5 backup log files
 
 
+def default_log_dir() -> Path:
+    """Return the default log directory resolved at runtime."""
+    return Path.home() / ".vlm" / "logs"
+
+
 class OperationContextFilter(logging.Filter):
     """Filter to add operation context to log records."""
     
@@ -57,10 +60,7 @@ def setup_logging(
     
     # Use default log directory if not specified
     if log_dir is None:
-        log_dir = DEFAULT_LOG_DIR
-    
-    # Create log directory if it doesn't exist
-    log_dir.mkdir(parents=True, exist_ok=True)
+        log_dir = default_log_dir()
     
     # Get root logger
     logger = logging.getLogger("vlm")
@@ -83,17 +83,23 @@ def setup_logging(
     logger.addHandler(console_handler)
     
     # File handler with rotation (DEBUG+)
-    log_file_path = log_dir / log_file
-    file_handler = logging.handlers.RotatingFileHandler(
-        filename=log_file_path,
-        maxBytes=MAX_LOG_SIZE,
-        backupCount=BACKUP_COUNT,
-        encoding='utf-8'
-    )
-    file_handler.setLevel(logging.DEBUG)
-    file_handler.setFormatter(formatter)
-    file_handler.addFilter(OperationContextFilter())
-    logger.addHandler(file_handler)
+    try:
+        log_dir.mkdir(parents=True, exist_ok=True)
+        log_file_path = log_dir / log_file
+        file_handler = logging.handlers.RotatingFileHandler(
+            filename=log_file_path,
+            maxBytes=MAX_LOG_SIZE,
+            backupCount=BACKUP_COUNT,
+            encoding='utf-8'
+        )
+        file_handler.setLevel(logging.DEBUG)
+        file_handler.setFormatter(formatter)
+        file_handler.addFilter(OperationContextFilter())
+        logger.addHandler(file_handler)
+    except (OSError, PermissionError) as exc:
+        logger.warning(
+            f"File logging disabled (cannot write to {log_dir}): {exc}"
+        )
     
     # Prevent propagation to root logger
     logger.propagate = False