fix: harden generic N-extruder device model and status/AMS UI, add N-toolhead ExtruderImage sizing, tests, and HLSD

docs/HLSD/multi-extruder-ams.md

@@ -144,10 +144,10 @@ The device-control widgets follow the same device-reported counts.
   `N3F_AMS`, `N3S_AMS`. A plain `AMS` maps to `GENERIC_AMS`.
 - On non-Bambu printers `use_generic_ams_layout()` routes `GENERIC_AMS` units through a variable-lane
   rendering that draws one lane per reported tray; Bambu keeps its fixed four-slot rendering.
-- `AMSControl` picks its layout by vendor: Bambu keeps the left/right presentation
-  (`CreateAmsSingleNozzle` for one toolhead, `CreateAmsDoubleNozzle` for two), while non-Bambu
-  printers use `CreateAmsMultiNozzle`, which builds one preview and one AMS simplebook per toolhead
-  for any count.
+- `AMSControl` picks its layout by toolhead count, not vendor: `CreateAmsSingleNozzle` for one
+  toolhead, `CreateAmsDoubleNozzle` for two, and `CreateAmsMultiNozzle` (one preview and one AMS
+  simplebook per toolhead) for three or more. A two-toolhead generic printer therefore keeps the
+  legacy left/right presentation; that is deliberate.
 - The status panel's `ExtruderImage` renders one per-toolhead state per nozzle and is resized to
   `GetTotalExtderCount()`. Non-Bambu printers choose the active toolhead through
   `m_generic_nozzle_selector` (shown when more than one toolhead exists); Bambu keeps its left/right
@@ -162,10 +162,14 @@ The device-control widgets follow the same device-reported counts.
 - **Extruder dialect invariants.** `device.extruder.state`'s count field must equal the length of
   `info[]`, and `info[]` must be ordered by extruder id with `id` equal to the array index: the
   parser places toolheads by array position while `GetExtderById()` indexes by id.
+- **One filament road per toolhead.** Each toolhead renders a single AMS filament road rather than an
+  independent per-toolhead road state. A generic scaffold that allowed the latter was removed as
+  unused; the one-extruder-per-toolhead road is the intended model.
 - **Preset/device agreement.** The generic layout and virtual-slot range derive their count from the
   selected printer preset. A printer preset must therefore declare the same number of
-  `nozzle_diameter` entries as the device has toolheads; a mismatch is surfaced because the sidebar
-  and extruder logic would otherwise disagree.
+  `nozzle_diameter` entries as the device has toolheads. A mismatch is surfaced only as a log warning
+  (`StatusPanel::check_extruder_count_mismatch()`), deliberately log-only, because the sidebar and
+  extruder logic would otherwise silently disagree.
 - **Bambu compatibility.** Bambu-specific presentation (left/right pair, fixed 4-slot units, fixed
   virtual ids, physical/logical inversion) is preserved behind the vendor check. Generic paths do
   not alter it.

src/slic3r/GUI/DeviceCore/DevFilaSystem.cpp

@@ -37,6 +37,9 @@ namespace Slic3r {
 
 bool devPrinterUtil::IsVirtualSlot(int ams_id)
 {
+    // When the app or preset bundle is unavailable we cannot know the vendor's
+    // extruder count, so fall back deterministically to the fixed Bambu pair
+    // {255, 254} rather than guessing from an unknown generic layout.
     if (wxTheApp == nullptr || GUI::wxGetApp().preset_bundle == nullptr || GUI::wxGetApp().preset_bundle->is_bbl_vendor())
         return ams_id == VIRTUAL_TRAY_MAIN_ID || ams_id == VIRTUAL_TRAY_DEPUTY_ID;
 
@@ -46,6 +49,14 @@ bool devPrinterUtil::IsVirtualSlot(int ams_id)
 
 bool devPrinterUtil::IsVirtualSlot(const std::string& ams_id)
 {
+    // Strict: only a fully numeric string is a valid slot id. std::stoi alone
+    // would accept trailing garbage (e.g. "255abc" -> 255).
+    if (ams_id.empty())
+        return false;
+    for (char c : ams_id) {
+        if (c < '0' || c > '9')
+            return false;
+    }
     try {
         return IsVirtualSlot(std::stoi(ams_id));
     } catch (...) {
@@ -220,6 +231,11 @@ wxString DevAms::GetDisplayName() const
 
 int DevAms::GetSlotCount() const
 {
+    // N3S is a 1-slot Bambu contract, so report 1 regardless of whether the
+    // preset bundle is momentarily unavailable (m_trays.size() can be 0).
+    if (GetAmsType() == N3S)
+        return 1;
+
     if (wxTheApp != nullptr && GUI::wxGetApp().preset_bundle != nullptr &&
         GUI::wxGetApp().preset_bundle->is_bbl_vendor()) {
         // GetAmsType() maps AMS_LITE_MIXED -> AMS_LITE, so N9 reports 4 slots like AMS-Lite.
@@ -228,10 +244,6 @@ int DevAms::GetSlotCount() const
         {
             return 4;
         }
-        else if (ams_type == N3S)
-        {
-            return 1;
-        }
     }
 
     return static_cast<int>(m_trays.size());
@@ -1057,7 +1069,7 @@ void DevFilaSystemParser::ParseAgentFilament(const json& data, MachineObject* ob
             if (!e.is_object())
                 continue;
             const int  ext   = e.value("extruder", MAIN_EXTRUDER_ID);
-            if (ext < MAIN_EXTRUDER_ID || ext > VIRTUAL_TRAY_MAIN_ID)
+            if (ext < MAIN_EXTRUDER_ID || ext >= VIRTUAL_TRAY_MAIN_ID)
                 continue;
 
             const int  vt_id = VIRTUAL_TRAY_MAIN_ID - ext;

src/slic3r/GUI/DeviceManager.cpp

@@ -808,8 +808,12 @@ bool MachineObject::is_extrusion_cali_finished()
 DevAmsTray *MachineObject::get_curr_tray()
 {
     const std::string& cur_ams_id = m_extder_system->GetCurrentAmsId();
-    if (cur_ams_id.compare(std::to_string(VIRTUAL_TRAY_MAIN_ID)) == 0) {
-        return &vt_slot[0];
+    if (devPrinterUtil::IsVirtualSlot(cur_ams_id)) {
+        for (auto& tray : vt_slot) {
+            if (tray.id == cur_ams_id)
+                return &tray;
+        }
+        return nullptr;
     }
 
     DevAms* curr_ams = get_curr_Ams();
@@ -2634,13 +2638,10 @@ void MachineObject::reset()
     json empty_j;
     print_json.diff2all_base_reset(empty_j);
 
-    for (auto i = 0; i < vt_slot.size(); i++) {
-        vt_slot[i].reset();
-
-        if (i == 1) {
-            vt_slot.erase(vt_slot.begin() + 1);
-        }
-    }
+    for (auto& tray : vt_slot)
+        tray.reset();
+    if (vt_slot.size() > 1)
+        vt_slot.erase(vt_slot.begin() + 1, vt_slot.end());
     // why: reset reuses MachineObject, so release its lazy subtask
     // before dropping the pointer to prevent reconnect leaks.
     if (subtask_) {

src/slic3r/GUI/StatusPanel.cpp

@@ -226,6 +226,8 @@ ExtruderImage::ExtruderImage(wxWindow* parent, wxWindowID id, int nozzle_num, co
     wxWindow::Create(parent, id, pos, wxSize(FromDIP(45), FromDIP(112)));
     SetBackgroundColour(*wxWHITE);
     m_nozzle_num = nozzle_num;
+    // Legacy Bambu single/dual page size. The generic (non-Bambu) grid grows
+    // past this when it holds more than two toolheads; see updateGenericSize().
     SetSize(wxSize(FromDIP(45), FromDIP(112)));
     SetMinSize(wxSize(FromDIP(45), FromDIP(112)));
     SetMaxSize(wxSize(FromDIP(45), FromDIP(112)));
@@ -298,6 +300,7 @@ void ExtruderImage::setExtruderCount(int nozzle_num)
 
     m_nozzle_num = normalized_count;
     m_multi_extruder_states.resize(static_cast<size_t>(m_nozzle_num), ExtruderState::EMPTY_LOAD);
+    updateGenericSize();
     Refresh();
 }
 
@@ -307,9 +310,37 @@ void ExtruderImage::setGenericNozzleDisplay(bool enabled)
         return;
 
     m_generic_nozzle_display = enabled;
+    updateGenericSize();
     Refresh();
 }
 
+void ExtruderImage::updateGenericSize()
+{
+    // The generic (non-Bambu) grid must stay legible for any toolhead count, so
+    // give it whole natural-size icons (24x62 DIP) and wrap into extra rows
+    // instead of squeezing everything into the fixed 45x112 Bambu page. doRender()
+    // balances the columns/rows inside the area we hand it, so sizing the page to
+    // a grid of natural-size cells keeps every icon at its full size.
+    // Bambu <=2 toolheads and generic <=2 toolheads keep the legacy page size.
+    wxSize size(FromDIP(45), FromDIP(112));
+    if (m_generic_nozzle_display && m_nozzle_num > 2) {
+        const wxSize icon = m_left_extruder_active_filled->GetBmpSize();
+        if (icon.x > 0 && icon.y > 0) {
+            // Fit as many columns as the fixed-width extruder panel (143 DIP) allows.
+            const int columns = std::max(1, std::min(m_nozzle_num, FromDIP(143) / icon.x));
+            const int rows    = (m_nozzle_num + columns - 1) / columns;
+            size = wxSize(columns * icon.x, rows * icon.y);
+        }
+    }
+
+    if (GetMinSize() == size && GetMaxSize() == size)
+        return;
+
+    SetMinSize(size);
+    SetMaxSize(size);
+    SetSize(size);
+}
+
 void ExtruderImage::setExtruderUsed(std::string loc)
 {
     //current_nozzle_idx = nozzle_id;
@@ -352,6 +383,7 @@ void ExtruderImage::update(ExtruderState state, int idx) {
         return;
 
     m_multi_extruder_states[idx] = state;
+    Refresh();
 }
 
 void ExtruderImage::paintEvent(wxPaintEvent& evt)
@@ -1954,6 +1986,8 @@ void StatusBasePanel::ensure_nozzle_temp_controls(size_t count)
     if (!m_temp_nozzle_parent || !m_temp_nozzle_sizer)
         return;
 
+    // Widgets beyond the current toolhead count are intentionally retained
+    // (hidden, never destroyed) so a later count increase reuses them.
     bool changed = count != m_temp_nozzle_active_count;
     while (m_tempCtrl_nozzles.size() < count) {
         TempInput* temp_ctrl = create_nozzle_temp_control(m_temp_nozzle_parent, m_nozzle_temp_control_id);
@@ -3715,6 +3749,9 @@ void StatusPanel::update_misc_ctrl(MachineObject *obj)
         ExtruderImage* image = m_extruderImage.front();
         image->setGenericNozzleDisplay(true);
         image->setExtruderCount(m_nozzle_num);
+        // Re-apply every update so a DPI change (which the setters above skip on
+        // steady state) still resizes the grid.
+        image->updateGenericSize();
 
         const int current_nozzle_id = extder_system->GetCurrentExtderId();
         const int selected_nozzle_id = current_nozzle_id >= 0 && current_nozzle_id < m_nozzle_num ? current_nozzle_id : -1;
@@ -3740,7 +3777,31 @@ void StatusPanel::update_misc_ctrl(MachineObject *obj)
             m_generic_nozzle_selector->Enable();
     }
 
-    if (bbl_selector_was_shown != m_nozzle_btn_panel->IsShown() ||
+    // The generic >2 toolhead page is larger than the legacy 45x112 Bambu page,
+    // so drive the book's size from the page that is shown. The book is only
+    // given an explicit size while a >2 generic grid is shown (or to clear a
+    // previous one); a plain Bambu session leaves the book's natural 45x112
+    // best size untouched.
+    bool book_size_changed = false;
+    {
+        const bool generic_grid       = !is_bbl_vendor && m_nozzle_num > 2;
+        const bool book_has_explicit_size =
+            m_extruder_book->GetMinSize() != wxDefaultSize ||
+            m_extruder_book->GetMaxSize() != wxDefaultSize;
+        if (generic_grid || book_has_explicit_size) {
+            const wxSize legacy_size(FromDIP(45), FromDIP(112));
+            const wxSize wanted_size = generic_grid ? m_extruderImage.front()->GetMinSize() : legacy_size;
+            if (m_extruder_book->GetMinSize() != wanted_size ||
+                m_extruder_book->GetMaxSize() != wanted_size) {
+                m_extruder_book->SetMinSize(wanted_size);
+                m_extruder_book->SetMaxSize(wanted_size);
+                book_size_changed = true;
+            }
+        }
+    }
+
+    if (book_size_changed ||
+        bbl_selector_was_shown != m_nozzle_btn_panel->IsShown() ||
         generic_selector_was_shown != m_generic_nozzle_selector->IsShown())
         m_nozzle_btn_panel->GetParent()->Layout();
 
@@ -3870,6 +3931,16 @@ void StatusPanel::update_ams(MachineObject *obj)
         AMSinfo info;
         info.ams_id = ams->first;
         if (ams->second->IsExist() && info.parse_ams_info(obj, ams->second, obj->GetFilaSystem()->IsDetectRemainEnabled(), obj->is_support_ams_humidity)) {
+            // A non-Bambu unit reported as AMS_LITE but not matching the fixed
+            // four-lane AMS_LITE grid (e.g. a generic unit advertising a
+            // different slot count) has no fixed layout to render into and would
+            // show an empty card. Treat it as GENERIC_AMS so it uses the same
+            // variable-lane rendering. Bambu's fixed rendering is untouched.
+            if (info.ams_type == AMSModel::AMS_LITE &&
+                info.cans.size() != GENERIC_AMS_SLOT_NUM &&
+                (!wxGetApp().preset_bundle || !wxGetApp().preset_bundle->is_bbl_vendor())) {
+                info.ams_type = AMSModel::GENERIC_AMS;
+            }
             ams_info.push_back(info);
         }
     }
@@ -3889,6 +3960,7 @@ void StatusPanel::update_ams(MachineObject *obj)
     const bool show_generic_nozzle_switch =
         obj->GetExtderSystem()->GetTotalExtderCount() > 2 &&
         !wxGetApp().preset_bundle->is_bbl_vendor();
+    const bool ams_nozzle_switch_was_shown = m_ams_nozzle_switch->IsShown();
     if (show_generic_nozzle_switch) {
         std::vector<wxString> nozzle_options;
         const int nozzle_count = obj->GetExtderSystem()->GetTotalExtderCount();
@@ -3903,7 +3975,8 @@ void StatusPanel::update_ams(MachineObject *obj)
     } else {
         m_ams_nozzle_switch->Hide();
     }
-    m_ams_nozzle_switch->GetParent()->Layout();
+    if (ams_nozzle_switch_was_shown != m_ams_nozzle_switch->IsShown())
+        m_ams_nozzle_switch->GetParent()->Layout();
     m_ams_control->UpdateAmsDryControl(obj);
 
     last_tray_exist_bits  = obj->tray_exist_bits;
@@ -5607,6 +5680,12 @@ void StatusPanel::on_nozzle_selected(wxCommandEvent &event)
             m_generic_nozzle_selector->Disable();
         if (obj->GetCtrl()->command_select_extruder(nozzle_id) == 0)
         {
+            if (!is_bbl_vendor) {
+                // The command did not start; restore the previous selection and
+                // re-enable the selector so the user is not stuck.
+                m_generic_nozzle_selector->SetSelection(current_selection);
+                m_generic_nozzle_selector->Enable();
+            }
             return;
         }
     }
@@ -5735,11 +5814,16 @@ void StatusPanel::set_default()
     m_switch_cham_fan_timeout = 0;
     m_show_ams_group = false;
     m_show_filament_group = false;
-    m_generic_nozzle_selector->Hide();
+    if (m_generic_nozzle_selector)
+        m_generic_nozzle_selector->Hide();
     m_nozzle_btn_panel->Hide();
-    m_generic_nozzle_selector->Clear();
+    if (m_generic_nozzle_selector)
+        m_generic_nozzle_selector->Clear();
     m_generic_nozzle_selector_count = 0;
     m_extruder_book->SetSelection(0);
+    // Clear any generic >2 toolhead grid growth from a previous device.
+    m_extruder_book->SetMinSize(wxSize(FromDIP(45), FromDIP(112)));
+    m_extruder_book->SetMaxSize(wxSize(FromDIP(45), FromDIP(112)));
     m_nozzle_btn_panel->GetParent()->Layout();
     reset_printing_values();
 
@@ -5765,7 +5849,8 @@ void StatusPanel::set_default()
     m_ams_control->Reset();
     m_ams_rack_switch->updateState("left");
     m_ams_rack_switch->Hide();
-    m_ams_nozzle_switch->Hide();
+    if (m_ams_nozzle_switch)
+        m_ams_nozzle_switch->Hide();
     m_panel_nozzle_rack->Hide();
     m_scale_panel->Hide();
     m_filament_load_box->Hide();

src/slic3r/GUI/StatusPanel.hpp

@@ -168,6 +168,7 @@ public:
     void update(ExtruderState state, int idx);
 
     void msw_rescale();
+    void updateGenericSize();
     void setExtruderCount(int nozzle_num);
     void setGenericNozzleDisplay(bool enabled);
     void setExtruderUsed(std::string loc);

src/slic3r/GUI/Widgets/AMSControl.cpp

@@ -638,6 +638,7 @@ void AMSControl::ClearAms() {
         for (auto &pane : m_nozzle_panes) {
             if (pane.preview_panel) pane.preview_panel->Destroy();
             if (pane.ams_book) pane.ams_book->Destroy();
+            if (pane.page) pane.page->Destroy();
         }
     }
     m_item_ids.assign(std::max(m_total_ext_count, 2), {});
@@ -1329,17 +1330,25 @@ void AMSControl::createAms(wxSimplebook* parent, int& idx, AMSinfo info, AMSPane
         // Above eight lanes, AmsItem is a fixed-minimum viewport over a wider
         // lane strip. Expand the viewport through its page's sizers rather
         // than propagating the strip's virtual width into the card/book.
+        // Reset back to the centered fixed layout for eight or fewer lanes so a
+        // later small unit is not left in expand mode.
         const bool generic_lane_layout = !wxGetApp().preset_bundle || !wxGetApp().preset_bundle->is_bbl_vendor();
-        if (generic_lane_layout && info.cans.size() > 8) {
+        if (generic_lane_layout) {
             if (auto *page = parent->GetParent()) {
                 auto pane = std::find_if(m_nozzle_panes.begin(), m_nozzle_panes.end(),
                     [page](const NozzleAmsPane &candidate) { return candidate.page == page; });
-                if (pane != m_nozzle_panes.end()) {
-                    pane->ams_area->GetItem(pane->ams_book)->SetProportion(1);
-                    pane->ams_area->GetItem(pane->ams_book)->SetFlag(wxEXPAND);
-                    pane->page_sizer->GetItem(pane->ams_area)->SetFlag(wxEXPAND | wxTOP);
-                    m_sizer_ams_items->GetItem(m_nozzle_book)->SetFlag(wxEXPAND);
-                    m_sizer_body->GetItem(m_sizer_ams_items)->SetFlag(wxEXPAND);
+                if (pane != m_nozzle_panes.end() && m_nozzle_book) {
+                    const bool expand_viewport = info.cans.size() > 8;
+                    if (auto *book_item = pane->ams_area->GetItem(pane->ams_book)) {
+                        book_item->SetProportion(expand_viewport ? 1 : 0);
+                        book_item->SetFlag(expand_viewport ? wxEXPAND : wxALIGN_CENTER);
+                    }
+                    if (auto *area_item = pane->page_sizer->GetItem(pane->ams_area))
+                        area_item->SetFlag(expand_viewport ? (wxEXPAND | wxTOP) : (wxALIGN_CENTER | wxTOP));
+                    if (auto *nozzle_book_item = m_sizer_ams_items->GetItem(m_nozzle_book))
+                        nozzle_book_item->SetFlag(expand_viewport ? wxEXPAND : wxALIGN_CENTER);
+                    if (auto *items_item = m_sizer_body->GetItem(m_sizer_ams_items))
+                        items_item->SetFlag(expand_viewport ? wxEXPAND : wxALIGN_CENTER);
                     m_amswin->Layout();
                 }
             }

src/slic3r/GUI/Widgets/MultiNozzleSync.cpp

@@ -877,7 +877,7 @@ void MultiNozzleStatusTable::UpdateRackInfo(std::weak_ptr<DevNozzleRack> rack)
             auto& nozzle = elem.second;
 
             int extruder_id{};
-            if (wxGetApp().preset_bundle->is_bbl_vendor()) {
+            if (wxGetApp().preset_bundle && wxGetApp().preset_bundle->is_bbl_vendor()) {
                 extruder_id = nozzle.AtLeftExtruder() ? 0 : 1;
                 if (nozzle.AtRightExtruder())
                     has_right = true;

tests/slic3rutils/test_dev_extder_system.cpp

@@ -3,7 +3,6 @@
 // makes std::byte a competing candidate (otherwise the Windows COM headers pulled in via
 // DeviceManager.hpp error with an ambiguous `byte`). wx/timer.h must precede DeviceManager.hpp,
 // which includes DeviceErrorDialog.hpp (uses wxTimerEvent) before its own wx/timer.h include.
-#include "catch2/catch_message.hpp"
 #include <string>
 #include <utility>
 #include <vector>
@@ -17,7 +16,6 @@
     #include <Windows.h>
 #endif
 
-#include <catch2/catch_test_macros.hpp>
 #include <catch2/catch_all.hpp>
 
 #include <wx/timer.h>
@@ -84,3 +82,77 @@ TEST_CASE("Extruder state decodes a generic toolhead set", "[DevExtderSystem]")
         CHECK(ext->GetNozzleId() == id);
     }
 }
+
+TEST_CASE("Legacy single-toolhead parser fills only the main extruder", "[DevExtderSystem]")
+{
+    MachineObject obj(nullptr, nullptr, "test", "test_dev", "127.0.0.1");
+    REQUIRE(obj.GetExtderSystem()->GetTotalExtderCount() == 1);
+
+    // ParseV1_0 is the legacy single/dual fallback. It returns unless the system reports exactly
+    // one toolhead, so it only ever writes MAIN_EXTRUDER_ID's fields.
+    const json legacy = {
+        {"nozzle_temper", 210},
+        {"nozzle_target_temper", 245},
+        {"ams", {{"tray_now", "2"}, {"tray_tar", "3"}}}
+    };
+    ExtderSystemParser::ParseV1_0(legacy, obj.GetExtderSystem());
+
+    const auto ext = obj.GetExtderSystem()->GetExtderById(MAIN_EXTRUDER_ID);
+    REQUIRE(ext.has_value());
+    CHECK(ext->GetCurrentTemp() == 210);
+    CHECK(ext->GetTargetTemp() == 245);
+
+    // Below 0x80 the tray pointer encodes ams_id = value / 4, slot_id = value % 4.
+    CHECK(ext->GetSlotNow().ams_id == "0");
+    CHECK(ext->GetSlotNow().slot_id == "2");
+    CHECK(ext->GetSlotTarget().ams_id == "0");
+    CHECK(ext->GetSlotTarget().slot_id == "3");
+    CHECK(obj.GetExtderSystem()->IsBusyLoading());
+    CHECK(obj.GetExtderSystem()->GetLoadingExtderId() == MAIN_EXTRUDER_ID);
+}
+
+// ParseV2_0 does not enforce the documented extruder dialect invariants: the count in `state` and
+// the id ordering of `info[]` are trusted, not checked. This test pins the resulting behavior.
+TEST_CASE("Malformed extruder payload is stored by info array position", "[DevExtderSystem]")
+{
+    const auto extder_info = [](int id) {
+        // Every key ParseV2_0 reads must be present.
+        return json{ {"id", id}, {"filam_bak", json::array()}, {"info", 0}, {"temp", 0},
+                     {"spre", 0}, {"snow", 0}, {"star", 0}, {"stat", 0}, {"hnow", 0} };
+    };
+
+    SECTION("state count disagrees with info length") {
+        MachineObject obj(nullptr, nullptr, "test", "test_dev", "127.0.0.1");
+
+        // `state` reports 2 toolheads but info[] carries 3.
+        json info = json::array();
+        for (int id = 0; id < 3; ++id)
+            info.push_back(extder_info(id));
+        ExtderSystemParser::ParseV2_0(json{ {"state", 2}, {"info", info} }, obj.GetExtderSystem());
+
+        // The info array wins: three toolheads are stored. m_total_extder_count still holds 2, so
+        // GetTotalExtderCount() would trip its debug assert; only the stored vector is inspected.
+        CHECK(obj.GetExtderSystem()->GetTotalExtderSize() == 3);
+        for (int id = 0; id < 3; ++id) {
+            const auto ext = obj.GetExtderSystem()->GetExtderById(id);
+            REQUIRE(ext.has_value());
+            CHECK(ext->GetExtId() == id);
+        }
+    }
+
+    SECTION("info id differs from the array index") {
+        MachineObject obj(nullptr, nullptr, "test", "test_dev", "127.0.0.1");
+
+        // ids 1 and 2 sit at array positions 0 and 1.
+        json info = json::array({extder_info(1), extder_info(2)});
+        ExtderSystemParser::ParseV2_0(json{ {"state", 2}, {"info", info} }, obj.GetExtderSystem());
+
+        // Toolheads are stored by array position; the payload id is kept but is not the lookup key.
+        const auto first = obj.GetExtderSystem()->GetExtderById(0);
+        REQUIRE(first.has_value());
+        CHECK(first->GetExtId() == 1);
+        const auto second = obj.GetExtderSystem()->GetExtderById(1);
+        REQUIRE(second.has_value());
+        CHECK(second->GetExtId() == 2);
+    }
+}

tests/slic3rutils/test_dev_mapping.cpp

@@ -3,8 +3,6 @@
 // makes std::byte a competing candidate (otherwise the Windows COM headers pulled in via
 // DeviceManager.hpp error with an ambiguous `byte`). wx/timer.h must precede DeviceManager.hpp,
 // which includes DeviceErrorDialog.hpp (uses wxTimerEvent) before its own wx/timer.h include.
-#include <string>
-#include <utility>
 #ifdef WIN32
     #ifndef WIN32_LEAN_AND_MEAN
         #define WIN32_LEAN_AND_MEAN
@@ -15,11 +13,14 @@
     #include <Windows.h>
 #endif
 
+#include <set>
+#include <string>
+#include <utility>
+#include <vector>
+
 #include <catch2/catch_test_macros.hpp>
 #include "slic3r/GUI/DeviceCore/DevDefs.h"
 #include "libslic3r/ProjectTask.hpp"
-#include <vector>
-#include <set>
 #include <catch2/catch_message.hpp>
 
 #include <catch2/catch_all.hpp>