fix(connection-selection): cache history, fix symlink persistence, hermetic tests

Address three unresolved code-review issues from PR #1374:

- Cache ProgramSettings.get_connection_history() once at widget init as
  _connection_history_cache instead of calling it (a disk read) on every
  3-second periodic port-refresh cycle, preventing potential UI stalls on
  slow disks or remote home directories.

- Update _connection_history_cache in-memory (prepend + deduplicate) in
  both reconnect() and add_connection() after calling store_connection(),
  keeping the cache consistent without further disk reads.

- Fix reconnect() to persist `selected_connection or device` instead of
  always persisting self.flight_controller.comport.device. This avoids
  storing resolved, unstable device paths (e.g. /dev/ttyACM0) when the
  user explicitly selected a /dev/serial/by-id/* symlink, preventing
  duplicates in the connection history.

- Patch ProgramSettings.store_connection in
  test_periodic_refresh_stops_on_connection to prevent writes to the real
  settings.json during tests, and assert the correct connection string was
  persisted to verify the fix above.

Author: amilcarlucas

ardupilot_methodic_configurator/frontend_tkinter_connection_selection.py

@@ -77,8 +77,10 @@ def __init__(  # pylint: disable=too-many-arguments, too-many-positional-argumen
         # Create a label for port
         port_label = ttk.Label(selection_frame, text=_("Port:"))
         port_label.pack(side=tk.LEFT, padx=(0, 5))
-        # Load saved connection history from ProgramSettings
-        for conn in ProgramSettings.get_connection_history():
+        # Load saved connection history from ProgramSettings and cache it to avoid
+        # repeated disk reads on every periodic port-refresh cycle.
+        self._connection_history_cache: list[str] = ProgramSettings.get_connection_history()
+        for conn in self._connection_history_cache:
             self.flight_controller.add_connection(conn)
 
         # Create a read-only combobox for flight controller connection selection
@@ -136,7 +138,7 @@ def _refresh_ports(self) -> None:
             current_selection = self.conn_selection_combobox.get_selected_key()
             self.flight_controller.discover_connections(
                 progress_callback=None,
-                preserved_connections=ProgramSettings.get_connection_history(),
+                preserved_connections=self._connection_history_cache,
             )
             new_connection_tuples = self.flight_controller.get_connection_tuples()
 
@@ -211,6 +213,10 @@ def add_connection(self) -> str:
         )
         if selected_connection:
             ProgramSettings.store_connection(selected_connection)
+            # Update cache in-memory (most-recent-first, deduplicated) to avoid a disk re-read.
+            self._connection_history_cache = [selected_connection] + [
+                c for c in self._connection_history_cache if c != selected_connection
+            ]
             error_msg = _("Will add new connection: {selected_connection} if not duplicated")
             logging_debug(error_msg.format(**locals()))
             self.flight_controller.add_connection(selected_connection)
@@ -261,11 +267,20 @@ def reconnect(self, selected_connection: str = "") -> bool:  # Default is auto-c
         # Store the current connection as the previous selection
         if self.flight_controller.comport and hasattr(self.flight_controller.comport, "device"):
             device: str = self.flight_controller.comport.device
-            self.previous_selection = device
+            # Prefer the user-selected connection string when available to avoid persisting
+            # a possibly resolved and unstable device path (e.g. /dev/ttyACM0 instead of
+            # the original /dev/serial/by-id/* symlink).  For auto-connect (empty
+            # selected_connection), fall back to the detected device path.
+            connection_identifier: str = selected_connection or device
+            self.previous_selection = connection_identifier
             # Persist the connection so it is available next time the program opens
             # and so it survives periodic auto-discovery refreshes during the current session.
-            ProgramSettings.store_connection(device)
-            self.flight_controller.add_connection(device)
+            ProgramSettings.store_connection(connection_identifier)
+            # Update cache in-memory (most-recent-first, deduplicated) to avoid a disk re-read.
+            self._connection_history_cache = [connection_identifier] + [
+                c for c in self._connection_history_cache if c != connection_identifier
+            ]
+            self.flight_controller.add_connection(connection_identifier)
         if self.destroy_parent_on_connect:
             self.parent.root.destroy()
         if self.download_params_on_connect and hasattr(self.parent, "download_flight_controller_parameters"):

tests/test_frontend_tkinter_connection_selection.py

@@ -991,6 +991,9 @@ def test_periodic_refresh_stops_on_connection(self) -> None:
                 "ardupilot_methodic_configurator.frontend_tkinter_connection_selection.ProgressWindow"
             ) as mock_progress_window,
             patch("ardupilot_methodic_configurator.frontend_tkinter_connection_selection.show_no_connection_error"),
+            patch(
+                "ardupilot_methodic_configurator.frontend_tkinter_connection_selection.ProgramSettings.store_connection"
+            ) as mock_store_connection,
         ):
             mock_progress_window.return_value.destroy = MagicMock()
 
@@ -1000,6 +1003,8 @@ def test_periodic_refresh_stops_on_connection(self) -> None:
             # Assert: Refresh should be stopped and timer cleared
             assert result is False  # Connection successful
             assert self.widget._refresh_timer_id is None
+            # Assert: The connection was persisted without filesystem side-effects in the test
+            mock_store_connection.assert_called_once_with("COM1")
 
     def test_periodic_refresh_stops_on_window_close(self) -> None:
         """