fix: printer agent switching on preset change

src/slic3r/GUI/GUI_App.cpp

@@ -3951,13 +3951,9 @@ void GUI_App::set_live_printer_agent(std::shared_ptr<IPrinterAgent> agent)
         m_agent->set_user_selected_machine("");
         // note: belt-and-suspenders (precedent: DeviceManagerRefresher::on_timer)
         dev->OnSelectedMachineLost(); // why: clear stale sidebar sync-status / AMS
-        // why: drop stale LAN discoveries; keep My Devices, but only those belonging to the
-        // agent we're about to swap to, so a device stamped by the outgoing agent doesn't
-        // linger hidden - the new agent's start_discovery re-inserts and re-stamps it fresh.
-        // agent is null when clearing the live agent entirely (e.g. plugin unload); there's no
-        // target to filter against then, so fall back to the original "keep all My Devices"
-        // behavior rather than guessing.
-        dev->clear_other_devices(agent ? agent->get_agent_info().id : std::string());
+        // why: retain agent-owned LAN discoveries so agents without automatic discovery (for
+        // example the Moonraker-based Qidi/Snapmaker agents) can reuse them after a switch.
+        dev->clear_other_devices();
     }
 
     m_agent->set_printer_agent(agent);
@@ -4013,8 +4009,10 @@ void GUI_App::switch_printer_agent()
         return;
     }
 
-    // The factory caches agents per ID, so an identical pointer means the agent type is unchanged.
-    if (m_agent->get_printer_agent() == new_printer_agent) {
+    // Compare the registered IDs, not only the implementation pointer. Different registry IDs
+    // may intentionally be backed by the same implementation object (especially for plugins).
+    const auto current_printer_agent = m_agent->get_printer_agent();
+    if (current_printer_agent && current_printer_agent->get_agent_info().id == effective_agent_id) {
         // Orca: the agent type is unchanged (e.g. switching between two Moonraker/Klipper
         // printer presets), so the selected machine and the agent's cached device_info still
         // point at the previously active printer preset. Re-select the machine when the new