Tighten exception handling flagged by Ruff

CONTRIBUTING.md

@@ -156,6 +156,12 @@ configured to write LF line endings so formatting is consistent across Windows
 and Linux. Fix reported lint problems in the code rather than weakening the
 shared rule set.
 
+Catch the narrowest expected exception in normal application code. A broad
+exception boundary is acceptable only where SchedPlus must keep a background
+service alive or provide a last-resort startup error report; those boundaries
+must log or report the failure and explain why the broad catch is intentional.
+Never silently discard an exception.
+
 ---
 
 ## Licensing Contributions

src/logic/reminder_service.py

@@ -1,5 +1,6 @@
 """Background reminder service that checks for upcoming tasks and sends notifications."""
 
+import logging
 import subprocess
 import sys
 import threading
@@ -12,6 +13,8 @@
 
 from . import local_time
 
+LOGGER = logging.getLogger(__name__)
+
 
 class ReminderService:
     """Polls for tasks due soon and sends native notifications."""
@@ -46,7 +49,7 @@ def _run(self) -> None:
             try:
                 self._check_tasks()
             except Exception:
-                pass
+                LOGGER.exception("Reminder check failed")
             time.sleep(self._poll_interval)
 
     def _check_tasks(self) -> None:
@@ -95,8 +98,8 @@ def _send_notification(self, title: str, date: str, time: str) -> None:
 
                 windll.user32.MessageBoxW(0, body, f"Reminder: {title}", 0x40 | 0x1000)
                 return
-            except Exception:
-                pass
+            except (AttributeError, ImportError, OSError):
+                LOGGER.exception("Windows reminder notification failed")
         if sys.platform == "darwin":
             try:
                 script = f'display notification "{self._escape_applescript(body)}" with title "{self._escape_applescript(title)}"'

src/logic/undo_manager.py

@@ -1,11 +1,14 @@
 """Undo manager for task actions with a bounded history stack."""
 
+import logging
 from dataclasses import dataclass
 from typing import TYPE_CHECKING
 
 if TYPE_CHECKING:
     from .scheduler import Scheduler, Task
 
+LOGGER = logging.getLogger(__name__)
+
 
 @dataclass
 class UndoAction:
@@ -67,7 +70,8 @@ def undo(self) -> str | None:
                 self._scheduler.complete_task(action.task_id)
                 return "Undid uncomplete"
         except Exception:
-            pass
+            self._history.append(action)
+            LOGGER.exception("Unable to undo %s action", action.action_type)
         return None
 
     def _push(self, action: UndoAction) -> None:

src/startup/controller.py

@@ -108,7 +108,7 @@ def _launch_mode(mode: StartupMode, arguments: list[str] | None = None):
     if mode == StartupMode.TK:
         try:
             from ui.tkinter_ui import run_ui
-        except Exception:
+        except ImportError:
             print("Tkinter UI is not available on this system.")
             return 1
 
@@ -119,7 +119,7 @@ def _launch_mode(mode: StartupMode, arguments: list[str] | None = None):
     elif mode == StartupMode.PYQT:
         try:
             from ui.pyqt_ui import run_pyqt_ui
-        except Exception as exc:
+        except ImportError as exc:
             print(f"PyQt UI is not available on this system: {exc}", file=sys.stderr)
             return 1
 
@@ -151,7 +151,7 @@ def _report_storage_error(mode: StartupMode, error: StorageError) -> None:
             messagebox.showerror("SchedPlus database error", str(error), parent=root)
             root.destroy()
             return
-        except Exception as reporter_exc:
+        except Exception as reporter_exc:  # noqa: BLE001 - last-resort error reporter
             print(
                 f"Unable to display the Tkinter database error: {reporter_exc}",
                 file=sys.stderr,
@@ -164,7 +164,7 @@ def _report_storage_error(mode: StartupMode, error: StorageError) -> None:
             QMessageBox.critical(None, "SchedPlus database error", str(error))
             app.quit()
             return
-        except Exception as reporter_exc:
+        except Exception as reporter_exc:  # noqa: BLE001 - last-resort error reporter
             print(
                 f"Unable to display the PyQt database error: {reporter_exc}",
                 file=sys.stderr,

src/startup/selector.py

@@ -13,7 +13,7 @@
 try:
     import tkinter as tk
     from tkinter import ttk
-except Exception:
+except ImportError:
     tk = None
     ttk = None
 

tests/test_reminder_service.py

@@ -107,7 +107,7 @@ def worker_add():
                 with service._lock:
                     service._notified.add(f"task-{i}")
                 time.sleep(0.0001)
-        except Exception as e:
+        except Exception as e:  # noqa: BLE001 - surface worker failures to the test
             errors.append(e)
 
     def worker_remove():
@@ -116,7 +116,7 @@ def worker_remove():
                 with service._lock:
                     service._notified.discard(f"task-{i}")
                 time.sleep(0.0001)
-        except Exception as e:
+        except Exception as e:  # noqa: BLE001 - surface worker failures to the test
             errors.append(e)
 
     threads = [threading.Thread(target=worker_add) for _ in range(3)] + [
@@ -165,10 +165,11 @@ def test_send_notification_linux_calls_notify_send(mock_run):
 
 @patch("logic.reminder_service.subprocess.run")
 def test_send_notification_windows_calls_message_box(mock_run):
-    with patch("sys.platform", "win32"):
+    with patch("sys.platform", "win32"), patch("ctypes.windll", create=True) as windll:
         service = ReminderService(MemoryScheduler())
         service._send_notification("Title", "2026-08-26", "12:00")
         mock_run.assert_not_called()  # uses ctypes directly
+        windll.user32.MessageBoxW.assert_called_once()
 
 
 def test_check_tasks_skips_completed_and_no_reminder():

tests/test_undo_manager.py

@@ -0,0 +1,35 @@
+from logic.undo_manager import UndoManager
+
+
+class RecordingScheduler:
+    def __init__(self):
+        self.deleted = []
+
+    def delete_task(self, task_id):
+        self.deleted.append(task_id)
+
+
+class FailingScheduler:
+    def delete_task(self, _task_id):
+        raise RuntimeError("storage unavailable")
+
+
+def test_successful_undo_consumes_action():
+    scheduler = RecordingScheduler()
+    manager = UndoManager(scheduler)
+    manager.record_add("task-1")
+
+    assert manager.undo() == "Undid add"
+    assert scheduler.deleted == ["task-1"]
+    assert not manager.can_undo()
+
+
+def test_failed_undo_is_logged_and_remains_available(caplog):
+    manager = UndoManager(FailingScheduler())
+    manager.record_add("task-1")
+
+    with caplog.at_level("ERROR"):
+        assert manager.undo() is None
+
+    assert manager.can_undo()
+    assert "Unable to undo add action" in caplog.text