fix: Temperature preheat command fires at correct time within long co…

include/ExtruderPlan.h

@@ -78,9 +78,11 @@ class ExtruderPlan
      *
      * \param path_idx The index into ExtruderPlan::paths which is currently being consider for temperature command insertion
      * \param gcode The gcode exporter to which to write the temperature command.
-     * \param cumulative_path_time The time spend on this path up to this point.
+     * \param cumulative_path_time The time spent on this path up to this point. Inserts whose path_idx is strictly less
+     *        than the current path_idx are considered overdue and will be fired unconditionally. Inserts whose path_idx
+     *        equals the current path_idx are fired only once cumulative_path_time reaches their time_after_path_start.
      */
-    void handleInserts(const size_t path_idx, GCodeExport& gcode, const double cumulative_path_time = std::numeric_limits<double>::infinity());
+    void handleInserts(const size_t path_idx, GCodeExport& gcode, const double cumulative_path_time);
 
     /*!
      * Insert all remaining temp inserts into gcode, to be called at the end of an extruder plan

src/ExtruderPlan.cpp

@@ -30,8 +30,21 @@ void ExtruderPlan::insertCommand(NozzleTempInsert&& insert)
 
 void ExtruderPlan::handleInserts(const size_t path_idx, GCodeExport& gcode, const double cumulative_path_time)
 {
-    while (! inserts_.empty() && path_idx >= inserts_.front().path_idx && inserts_.front().time_after_path_start < cumulative_path_time)
-    { // handle the Insert to be inserted before this path_idx (and all inserts not handled yet)
+    while (! inserts_.empty())
+    {
+        const NozzleTempInsert& insert = inserts_.front();
+        if (insert.path_idx > path_idx)
+        {
+            // Insert is scheduled for a future path; nothing more to do for now.
+            break;
+        }
+        if (insert.path_idx == path_idx && insert.time_after_path_start > cumulative_path_time)
+        {
+            // Insert is scheduled for this path, but the required time within the path has not been reached yet.
+            break;
+        }
+        // Either the insert is overdue (insert.path_idx < path_idx) and must be fired immediately,
+        // or it is exactly on time (insert.path_idx == path_idx and time threshold reached).
         inserts_.front().write(gcode);
         inserts_.pop_front();
     }

src/LayerPlan.cpp

@@ -3512,7 +3512,9 @@ void LayerPlan::writeGCode(GCodeExport& gcode)
 
         for (size_t path_idx = 0; path_idx < paths.size(); path_idx++)
         {
-            extruder_plan.handleInserts(path_idx, gcode);
+            // Fire any inserts that became overdue during the previous path, using the total
+            // accumulated time from that path.
+            extruder_plan.handleInserts(path_idx, gcode, cumulative_path_time);
             cumulative_path_time = 0.; // reset to 0 for current path.
 
             GCodePath& path = paths[path_idx];