Fix crash on printer switch from stale filament/extruder indices (#14103)

Switching to a printer with fewer filaments (e.g. H2D -> X2D) threw
std::out_of_range in check_filament_printable. Clear stale per-volume
extruder config on count shrink and bound-check filament indices at the
read sites.

src/libslic3r/Model.cpp

@@ -2573,6 +2573,12 @@ void ModelVolume::update_extruder_count(size_t extruder_count)
             break;
         }
     }
+    // Clear a stale per-volume filament assignment that no longer exists after the extruder count
+    // shrank (e.g. printer switch to one with fewer filaments), so downstream readers never index
+    // per-filament config vectors out of range. Ported from BambuStudio (STUDIO-15763).
+    if (extruder_id() > extruder_count) {
+        this->config.erase("extruder");
+    }
 }
 
 void ModelVolume::update_extruder_count_when_delete_filament(size_t extruder_count, size_t filament_id, int replace_filament_id)
@@ -2584,6 +2590,11 @@ void ModelVolume::update_extruder_count_when_delete_filament(size_t extruder_cou
             break;
         }
     }
+    // Same stale-assignment cleanup as update_extruder_count, for the filament-delete path.
+    // Ported from BambuStudio (STUDIO-15763).
+    if (extruder_id() > extruder_count) {
+        this->config.erase("extruder");
+    }
 }
 
 void ModelVolume::center_geometry_after_creation(bool update_source_offset)

src/slic3r/GUI/GCodeViewer.cpp

@@ -2639,8 +2639,14 @@ void GCodeViewer::render_all_plates_stats(const std::vector<const GCodeProcessor
         {
             auto plate_print_statistics = plate->get_slice_result()->print_statistics;
             auto plate_extruders = plate->get_extruders(true);
+            auto max_extruders_colors = wxGetApp().plater()->get_extruders_colors().size();
             for (size_t extruder_id : plate_extruders) {
                 extruder_id -= 1;
+                // Skip stale/overflow extruder indices (e.g. from object assignments that outlived a
+                // filament-count change) so downstream per-extruder lookups stay in range. Ported
+                // from BambuStudio (STUDIO-15763).
+                if (extruder_id >= max_extruders_colors)
+                    continue;
                 if (plate_print_statistics.model_volumes_per_extruder.find(extruder_id) == plate_print_statistics.model_volumes_per_extruder.end())
                     model_volume_of_extruders_all_plates[extruder_id] += 0;
                 else {

src/slic3r/GUI/GUI_ObjectList.cpp

@@ -764,6 +764,10 @@ void ObjectList::update_filament_values_for_items(const size_t filaments_count)
                 if (!object->volumes[id]->config.has("extruder") ||
                     size_t(object->volumes[id]->config.extruder()) > filaments_count) {
                     extruder = wxString::Format("%d", object->config.extruder());
+                    // Clear the stale per-volume assignment so it falls back to the object's
+                    // extruder; otherwise the out-of-range index survives. Ported from
+                    // BambuStudio (STUDIO-15763).
+                    object->volumes[id]->config.erase("extruder");
                 }
                 else {
                     extruder = wxString::Format("%d", object->volumes[id]->config.extruder());

src/slic3r/GUI/PartPlate.cpp

@@ -1931,11 +1931,20 @@ bool PartPlate::check_filament_printable(const DynamicPrintConfig &config, wxStr
 
     std::vector<int> used_filaments = get_extruders(true);  // 1 base
     if (!used_filaments.empty()) {
+        const std::vector<std::string>& filament_types      = config.option<ConfigOptionStrings>("filament_type")->values;
+        const std::vector<int>&         filament_printables = config.option<ConfigOptionInts>("filament_printable")->values;
+        const std::vector<int>&         filament_map        = get_real_filament_maps(config);
+        // This runs synchronously mid printer-switch (load_current_preset -> reload_scene), before the
+        // filament-count reconciliation clears stale per-object assignments, so the plate objects can
+        // still reference filament indices beyond the freshly selected printer config. Skip those to
+        // avoid an out-of-range access. Matches BambuStudio's guards in the same function.
+        const int filament_count = std::min({(int) filament_types.size(), (int) filament_printables.size(), (int) filament_map.size()});
         for (auto filament_idx : used_filaments) {
             int filament_id = filament_idx - 1;
-            std::string filament_type = config.option<ConfigOptionStrings>("filament_type")->values.at(filament_id);
-            int filament_printable_status = config.option<ConfigOptionInts>("filament_printable")->values.at(filament_id);
-            std::vector<int> filament_map  = get_real_filament_maps(config);
+            if (filament_id < 0 || filament_id >= filament_count)
+                continue;
+            std::string filament_type = filament_types[filament_id];
+            int filament_printable_status = filament_printables[filament_id];
             int extruder_idx = filament_map[filament_id] - 1;
             if (!(filament_printable_status >> extruder_idx & 1)) {
                 wxString extruder_name = extruder_idx == 0 ? _L("left") : _L("right");