Disconnect from the device when opening a file or closing the app

Opening a file now drops the live connection once a file is chosen, without
asking. File > Exit and the window close box go through quit_app, which
closes the Sox session properly instead of leaving it for the device to
time out.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

main.py

@@ -2435,6 +2435,30 @@ def do_device_disconnect():
     wiresheet.render_components([])
 
 
+def quit_app():
+    """File > Exit and the window's close box: let go of the device before going.
+
+    Leaving without a proper close keeps the device's Sox session and subscriptions
+    alive until it times them out, so the next connect may be turned away.
+    """
+    global _cov_poll_id
+
+    if _cov_poll_id is not None:
+        app_state.window.after_cancel(_cov_poll_id)
+        _cov_poll_id = None
+
+    ds = app_state.device_session
+    app_state.device_session = None
+    app_state.live_mode = False
+    if ds is not None:
+        try:
+            ds.disconnect()
+        except Exception:
+            pass
+
+    app_state.window.destroy()
+
+
 def _start_cov_polling():
     """Starts the 100ms COV event polling loop on the main thread."""
     global _cov_poll_id
@@ -2616,7 +2640,7 @@ menu_file.add_command(label="Save As...", command=sax_file.save_file_as)
 menu_file.add_separator()
 menu_file.add_command(label="Print...", command=wiresheet.print_sheet, accelerator=f"{accel_mod}+P")
 menu_file.add_separator()
-menu_file.add_command(label="Exit", command=window.quit)
+menu_file.add_command(label="Exit", command=quit_app)
 menu_bar.add_cascade(label="File", menu=menu_file)
 
 menu_edit = tk.Menu(menu_bar, tearoff=0)
@@ -3000,6 +3024,8 @@ paned_window.add(frame_editor, weight=3)
 app_state.dirty_display_callback = refresh_dirty_display
 undo.set_refresh_callback(refresh_all_views)
 sax_file.set_tree_filled_callback(on_tree_filled)
+sax_file.set_disconnect_device_callback(do_device_disconnect)
+window.protocol("WM_DELETE_WINDOW", quit_app)
 refresh_palette_kits()
 apply_left_pane_width()