Bracket a toolchange's own gcode against FanMover splitting its moves (#15904)

FanMover could split a move inside change_filament_gcode to place a delayed fan command. It computed the split point from the last position the G-code set, but on Bambu printers the firmware moves the head during the T command, so the inserted waypoint sent the head to a spot the template never visits (#15789).

Both toolchange paths, set_extruder() and the Type1 append_tcr(), now wrap the template output in ;_FAN_MOVER_SKIP_START/END tags when fan speed-up or kick-start is on. FanMover keeps fan commands inside them where they are and drops the tags from the output. multifilament_config() also sizes the per-filament options that the wipe tower reads by index.

src/libslic3r/GCode.cpp

@@ -1033,6 +1033,15 @@ static std::vector<Vec2d> get_path_of_change_filament(const Print& print)
         return buf;
     }
 
+    // FanMover consumes these markers (and drops them) to avoid splitting a G1 inside custom gcode.
+    // Only written when FanMover runs, the same gate as its construction in GCode::process_layers.
+    static std::string wrap_custom_gcode_for_fan_mover(const FullPrintConfig &config, const std::string &gcode)
+    {
+        if (config.fan_speedup_time.value == 0 && config.fan_kickstart.value <= 0)
+            return gcode;
+        return ";_FAN_MOVER_SKIP_START\n" + gcode + ";_FAN_MOVER_SKIP_END\n";
+    }
+
     std::string WipeTowerIntegration::append_tcr(GCode& gcodegen, const WipeTower::ToolChangeResult& tcr, int new_filament_id, double z) const
     {
         if (new_filament_id != -1 && new_filament_id != tcr.new_tool)
@@ -1384,6 +1393,9 @@ static std::vector<Vec2d> get_path_of_change_filament(const Print& print)
             toolchange_gcode_str = gcodegen.placeholder_parser_process("change_filament_gcode", change_filament_gcode, new_filament_id, &config);
 
             check_add_eol(toolchange_gcode_str);
+            // Type1 wipe tower path (every BBL printer): bracket the same way set_extruder() does,
+            // so FanMover doesn't split a G1 inside this custom gcode either.
+            toolchange_gcode_str = wrap_custom_gcode_for_fan_mover(gcodegen.config(), toolchange_gcode_str);
 
             //BBS
             {
@@ -10895,7 +10907,8 @@ std::string GCode::set_extruder(unsigned int new_filament_id, double print_z, bo
 
         toolchange_gcode_parsed = placeholder_parser_process("change_filament_gcode", change_filament_gcode, new_filament_id, &dyn_config);
         check_add_eol(toolchange_gcode_parsed);
-        gcode += toolchange_gcode_parsed;
+        // toolchange_gcode_parsed is still read below (get_last_z_from_gcode, custom_gcode_changes_tool).
+        gcode += wrap_custom_gcode_for_fan_mover(m_config, toolchange_gcode_parsed);
 
         //BBS
         {

src/libslic3r/GCode/FanMover.cpp

@@ -445,6 +445,11 @@ void FanMover::_process_gcode_line(GCodeReader& reader, const GCodeReader::GCode
                 std::string extrusion_string = line.raw().substr(6, line.raw().size() - 6);
                 current_role = ExtrusionEntity::string_to_role(extrusion_string);
             }
+            if (line.raw().rfind(";_FAN_MOVER_SKIP_", 0) == 0) {
+                // Internal markers: read here, then dropped from the output.
+                m_is_custom_gcode = line.raw().rfind(";_FAN_MOVER_SKIP_START", 0) == 0;
+                time = -1;
+            }
             if (line.raw().size() > 16) {
                 if (line.raw().rfind("; custom gcode", 0) != std::string::npos) {
                     if (line.raw().rfind("; custom gcode end", 0) != std::string::npos)