Restore Plugin HTML After a WebKit Reload

Plugin dialog content is injected with SetPage, so on the WebKit backends a
reload (context menu, keyboard shortcut or location.reload()) re-fetches the
SetPage base URL instead of the injected document, and the plugin UI is gone
for good: load_plugin_content() returned early once m_content_loaded was set.

On GTK and macOS, re-inject the plugin HTML when a main-frame load arrives
after the initial swap. m_own_page_load marks the load caused by our own
SetPage so it is not mistaken for a reload, and a post-load error is left
alone, as it only ever means a failed subresource.

MSW is left out: WebView2 reloads NavigateToString content from its own
history entry, so the page already survives a reload there, and the backend
reports in-document navigation (a page setting location.hash) as a load,
which re-injection would turn into a page wipe.

src/slic3r/GUI/PluginWebDialog.cpp

@@ -139,19 +139,32 @@ void PluginWebDialog::destroy_for_plugin(PluginWebDialog* dialog)
 
 void PluginWebDialog::on_bootstrap_event(wxWebViewEvent& event)
 {
-    // The first bootstrap load (or its error) triggers the swap to plugin HTML;
+    // The first bootstrap load (or its error) triggers the swap to plugin HTML.
-    // the resulting plugin-page load is ignored (guarded by m_content_loaded).
+    if (!m_content_loaded)
-    load_plugin_content();
+        load_plugin_content();
+#ifndef __WXMSW__
+    // WebKit reloads the SetPage base URL rather than the injected page, so a later main-frame
+    // load that is not our own SetPage is a browser reload, and the plugin HTML has to be put
+    // back. A post-load error only ever means a failed subresource. WebView2 reloads SetPage
+    // content from its own history entry, and reports in-document navigation as a load, so
+    // MSW needs neither the re-injection nor a guard against it.
+    else if (event.GetEventType() == wxEVT_WEBVIEW_LOADED) {
+        if (m_own_page_load)
+            m_own_page_load = false;
+        else
+            load_plugin_content();
+    }
+#endif
     event.Skip();
 }
 
 void PluginWebDialog::load_plugin_content()
 {
-    if (m_content_loaded)
-        return;
     m_content_loaded = true;
-    if (wxWebView* wv = browser())
+    if (wxWebView* wv = browser()) {
+        m_own_page_load = true;
         wv->SetPage(wxString::FromUTF8(m_html), web_base_url());
+    }
 }
 
 void PluginWebDialog::on_script_message(const nlohmann::json& payload)

src/slic3r/GUI/PluginWebDialog.hpp

@@ -72,6 +72,7 @@ private:
 
     std::string                   m_html;
     bool                          m_content_loaded{false};
+    bool                          m_own_page_load{false}; // a SetPage of the plugin HTML is in flight
     bool                          m_open{true};
     bool                          m_close_fired{false};
     std::optional<nlohmann::json> m_result;