Improve handling of fatal exceptions (as showing the GUI, even on the main thread, can fail),

making sure that the error is furthermore logged or at least written to stderr

src/serena/agent.py

@@ -6,6 +6,7 @@ import inspect
 import json
 import os
 import platform
+import sys
 import traceback
 from abc import ABC
 from collections import defaultdict
@@ -16,6 +17,7 @@ from typing import TYPE_CHECKING, Any, Self, TypeVar, Union, cast
 
 import yaml
 from sensai.util import logging
+from sensai.util.logging import FallbackHandler
 from sensai.util.string import ToStringMixin, dict_string
 
 from multilspy import SyncLanguageServer
@@ -40,6 +42,27 @@ TTool = TypeVar("TTool", bound="Tool")
 SUCCESS_RESULT = "OK"
 
 
+def show_fatal_exception_safe(e: Exception) -> None:
+    """
+    Shows the given exception in the GUI log viewer on the main thread and ensures that the exception is logged or at
+    least printed to stderr.
+    """
+    # Make sure the error is logged (adding a fallback handler which writes to stderr in case there is no other handler)
+    fallback_handler = FallbackHandler(logging.StreamHandler(sys.stderr))
+    Logger.root.addHandler(fallback_handler)
+    log.error(f"Fatal exception: {e}", exc_info=e)
+
+    # attempt to show the error in the GUI
+    try:
+        # NOTE: The import can fail on macOS if Tk is not available (depends on Python interpreter installation, which uv
+        #   used as a base); while tkinter as such is always available, its dependencies can be unavailable on macOS.
+        from serena.gui_log_viewer import show_fatal_exception
+
+        show_fatal_exception(e)
+    except:
+        pass
+
+
 class SerenaConfigError(Exception):
     pass
 
@@ -171,7 +194,8 @@ class SerenaAgent:
             if platform.system() == "Darwin":
                 log.warning("GUI log window is not supported on macOS")
             else:
-                # even importing on macOS may fail since tkinter is not available by default
+                # even importing on macOS may fail if tkinter dependencies are unavailable (depends on Python interpreter installation
+                # which uv used as a base, unfortunately)
                 from serena.gui_log_viewer import GuiLogViewer, GuiLogViewerHandler
 
                 log_level = self.serena_config.gui_log_window_level

src/serena/agno.py

@@ -15,8 +15,7 @@ from dotenv import load_dotenv
 from sensai.util.logging import LogTime
 
 from serena import serena_root_path
-from serena.agent import SerenaAgent, Tool
-from serena.gui_log_viewer import show_fatal_exception
+from serena.agent import SerenaAgent, Tool, show_fatal_exception_safe
 
 log = logging.getLogger(__name__)
 
@@ -92,7 +91,7 @@ class SerenaAgnoAgentProvider:
                 try:
                     serena_agent = SerenaAgent(project_file)
                 except Exception as e:
-                    show_fatal_exception(e)
+                    show_fatal_exception_safe(e)
                     raise
 
             # Even though we don't want to keep history between sessions,

src/serena/mcp.py

@@ -15,8 +15,7 @@ from mcp.server.fastmcp.utilities.func_metadata import func_metadata
 from sensai.util import logging
 from sensai.util.helper import mark_used
 
-from serena.agent import SerenaAgent, Tool
-from serena.gui_log_viewer import show_fatal_exception
+from serena.agent import SerenaAgent, Tool, show_fatal_exception_safe
 
 log = logging.getLogger(__name__)
 LOG_FORMAT = "%(levelname)-5s %(asctime)-15s %(name)s:%(funcName)s:%(lineno)d - %(message)s"
@@ -100,7 +99,7 @@ def create_mcp_server() -> FastMCP:
             # project_activation_callback=update_tools
         )
     except Exception as e:
-        show_fatal_exception(e)
+        show_fatal_exception_safe(e)
         raise
 
     @asynccontextmanager