fix: QThread crash on iPod connect and device detection — proper wait() lifecycle

Root cause: QThread C++ destructor ran while underlying OS thread was
still terminating. The pattern of checking isRunning() and using
short timeouts (wait(3000/5000)) left a window where the Python
reference was dropped and Shiboken destroyed the C++ object before
the thread fully exited.

Fixes:
- Remove all self.finished.connect(self.deleteLater) — unsafe,
  deleteLater from within run() or from worker thread races with
  thread termination
- _cleanup_worker: always call wait() (no timeout) before nulling
  the Python reference — guarantees OS thread is fully dead
- Add _is_worker_running() helper with try/except RuntimeError
  guard to safely check stale C++ objects
- DeviceMonitor._poll/stop/wait: use wait() with no timeout
- closeEvent: guard isRunning() with try/except RuntimeError

src/ui/ipod_tab.py

@@ -107,7 +107,7 @@ class iPodTab(QWidget):
         layout.addWidget(self.delete_status)
 
     def _on_refresh_devices_clicked(self):
-        if self.worker_thread and self.worker_thread.isRunning():
+        if self._is_worker_running():
             return
 
         self.device_combo.clear()
@@ -122,6 +122,8 @@ class iPodTab(QWidget):
         self.device_info_label.setText(status)
 
     def _on_device_detection_finished(self, success, message, result):
+        self._cleanup_worker()
+
         if success:
             self.ipod_devices = result
             self.device_combo.clear()
@@ -140,8 +142,6 @@ class iPodTab(QWidget):
         else:
             self._set_device_not_found()
 
-        self._cleanup_worker()
-
     def _start_mount_and_load(self, device: dict, mount_point=None, already_mounted=False):
         self.device_status_label.setText("Mounting and loading tracks...")
         self.mount_button.setEnabled(False)
@@ -320,11 +320,12 @@ class iPodTab(QWidget):
         if reply != QMessageBox.StandardButton.Yes:
             return
 
-        if self.worker_thread and self.worker_thread.isRunning():
+        if self._is_worker_running():
             QMessageBox.information(self, "Info", "Please wait for the current task to finish")
             return
 
         pids = []
+
         for item in selected:
             track_data = item.data(Qt.ItemDataRole.UserRole)
             if track_data and "pid" in track_data:
@@ -391,7 +392,7 @@ class iPodTab(QWidget):
             QMessageBox.warning(self, "Error", "No valid track files found on device")
             return
 
-        if self.worker_thread and self.worker_thread.isRunning():
+        if self._is_worker_running():
             QMessageBox.information(self, "Info", "Please wait for the current task to finish")
             return
 
@@ -470,7 +471,7 @@ class iPodTab(QWidget):
             QMessageBox.warning(self, "Error", "No iPod device mounted.")
             return
 
-        if self.worker_thread and self.worker_thread.isRunning():
+        if self._is_worker_running():
             QMessageBox.information(self, "Info", "Please wait for the current task to finish")
             return
 
@@ -506,12 +507,20 @@ class iPodTab(QWidget):
             pass
 
     def _on_auto_state_changed(self, devices):
-        if self.worker_thread and self.worker_thread.isRunning():
+        if self._is_worker_running():
             return
         self._on_device_detection_finished(True, f"Found {len(devices)} devices", devices)
 
     def _cleanup_worker(self):
         if self.worker_thread:
-            self.worker_thread.wait(3000)
-            self.worker_thread.deleteLater()
+            self.worker_thread.quit()
+            self.worker_thread.wait()
             self.worker_thread = None
+
+    def _is_worker_running(self):
+        if self.worker_thread:
+            try:
+                return self.worker_thread.isRunning()
+            except RuntimeError:
+                self.worker_thread = None
+        return False

src/ui/library_tab.py

@@ -957,7 +957,7 @@ class LibraryTab(QWidget):
             )
             return
 
-        if self.worker_thread and self.worker_thread.isRunning():
+        if self._is_worker_running():
             QMessageBox.information(self, "Info", "Please wait for the current task to finish")
             return
 
@@ -1025,7 +1025,7 @@ class LibraryTab(QWidget):
             QMessageBox.warning(self, "Error", "No iPod device mounted. Go to iPod tab and mount first.")
             return
 
-        if self.worker_thread and self.worker_thread.isRunning():
+        if self._is_worker_running():
             QMessageBox.information(self, "Info", "Please wait for the current task to finish")
             return
 
@@ -1070,7 +1070,7 @@ class LibraryTab(QWidget):
             QMessageBox.warning(self, "Error", "No iPod device mounted.")
             return
 
-        if self.worker_thread and self.worker_thread.isRunning():
+        if self._is_worker_running():
             QMessageBox.information(self, "Info", "Please wait for the current task to finish")
             return
 
@@ -1140,10 +1140,18 @@ class LibraryTab(QWidget):
 
     def _cleanup_worker(self):
         if self.worker_thread:
-            self.worker_thread.wait(3000)
-            self.worker_thread.deleteLater()
+            self.worker_thread.quit()
+            self.worker_thread.wait()
             self.worker_thread = None
 
+    def _is_worker_running(self):
+        if self.worker_thread:
+            try:
+                return self.worker_thread.isRunning()
+            except RuntimeError:
+                self.worker_thread = None
+        return False
+
     def on_device_mounted(self, mount_point: str):
         self._current_mount_point = mount_point
         self.library_progress.setVisible(True)