Warn when a filament will switch extruders mid-print

src/slic3r/GUI/PrePrintChecker.hpp

@@ -111,6 +111,7 @@ enum PrintDialogStatus : unsigned int {
     PrintStatusFilamentWarningUnknownHighChamberTempSoft,
     PrintStatusWarningExtFilamentNotMatch,
     PrintStatusFilamentWarningNozzleHRC,
+    PrintStatusFilamentCrossExtruderWarning,
     PrintStatusFilamentWarningEnd,
 
     PrintStatusWarningEnd,//->end error<-

src/slic3r/GUI/SelectMachine.cpp

@@ -1875,6 +1875,22 @@ bool SelectMachineDialog::check_sdcard_for_timelpase(MachineObject* obj)
     return false;
 }
 
+bool SelectMachineDialog::CheckWarningFilamentCrossExtruder(MachineObject* obj_)
+{
+    if (!obj_ || m_print_type != PrintFromType::FROM_NORMAL) return true;
+    if (obj_->GetExtderSystem()->GetTotalExtderCount() != 2) return true;
+
+    for (const auto& fila : m_ams_mapping_result) {
+        std::set<int> used_extruder_ids;
+        for (const auto& [pos_id, nozzle] : get_mapped_nozzles(fila.id)) {
+            if (!nozzle.IsEmpty()) { used_extruder_ids.insert(nozzle.GetExtruderId()); }
+        }
+        if (used_extruder_ids.size() >= 2) { return false; }
+    }
+
+    return true;
+}
+
 void SelectMachineDialog::show_status(PrintDialogStatus status, std::vector<wxString> params, wxString wiki_url)
 {
     wxString msg;
@@ -2115,6 +2131,10 @@ void SelectMachineDialog::show_status(PrintDialogStatus status, std::vector<wxSt
         // Advisory rack inventory shortfalls: allow Send.
         Enable_Refresh_Button(true);
         Enable_Send_Button(true);
+    } else if (status == PrintDialogStatus::PrintStatusFilamentCrossExtruderWarning) {
+        // Advisory only: per-nozzle K can't follow a filament across extruders.
+        Enable_Refresh_Button(true);
+        Enable_Send_Button(true);
     }
 
     /*enter perpare mode*/
@@ -4247,6 +4267,11 @@ void SelectMachineDialog::update_show_status(MachineObject* obj_)
           //  return;
         }
     }
+    if (!CheckWarningFilamentCrossExtruder(obj_)) {
+        wxString warning_msg = _L("Some filaments may switch between extruders during printing. Manual K-value calibration cannot be applied throughout the entire print, which "
+                                  "may affect print quality. Enabling Flow Dynamics Calibration is recommended.");
+        show_status(PrintDialogStatus::PrintStatusFilamentCrossExtruderWarning, { warning_msg });
+    }
     if (m_ams_mapping_res) {
         if (has_timelapse_warning()) {
             show_status(PrintDialogStatus::PrintStatusTimelapseWarning);

src/slic3r/GUI/SelectMachine.hpp

@@ -531,6 +531,9 @@ public:
     // Compare the slicing file's nozzle requirements (validity, flow, diameter) against the
     // printer; the rack extruder is checked against its whole inventory (mounted + rack).
     bool CheckErrorExtruderNozzleWithSlicing(MachineObject* obj_);//return true if no errors
+    // Warn (without blocking) when a mapped filament would be printed from both extruders on a
+    // dual-extruder printer, so per-nozzle manual K-value can't follow it across the whole print.
+    bool CheckWarningFilamentCrossExtruder(MachineObject* obj_);
 
     // Rack print-dispatch nozzle mapping (H2C): request the printer's auto-mapping and consume the
     // result, gating the Send button while the printer computes. Both are no-ops for non-rack printers.