Fix wipe tower placed outside bed boundary on first slice (#12777)

# Description

The wipe tower config position (wipe_tower_x/y) could be outside the plate boundary (e.g. default y=250 on a 200mm printer). No constraint was applied at slice time, so the tower was generated out-of-bounds.

issue reported in #12731

# Screenshots/Recordings/Graphs

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## Tests

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src/slic3r/GUI/GLCanvas3D.cpp

@@ -2835,6 +2835,12 @@ void GLCanvas3D::reload_scene(bool refresh_immediately, bool force_full_scene_re
                 DynamicPrintConfig& proj_cfg = wxGetApp().preset_bundle->project_config;
                 float x = dynamic_cast<const ConfigOptionFloats*>(proj_cfg.option("wipe_tower_x"))->get_at(plate_id);
                 float y = dynamic_cast<const ConfigOptionFloats*>(proj_cfg.option("wipe_tower_y"))->get_at(plate_id);
+                // Helper: persist corrected wipe tower position to config so the next slice uses valid coords.
+                auto persist_wipe_tower_pos = [&](float nx, float ny) {
+                    ConfigOptionFloat cx(nx), cy(ny);
+                    proj_cfg.option<ConfigOptionFloats>("wipe_tower_x")->set_at(&cx, plate_id, 0);
+                    proj_cfg.option<ConfigOptionFloats>("wipe_tower_y")->set_at(&cy, plate_id, 0);
+                };
                 float w = dynamic_cast<const ConfigOptionFloat*>(m_config->option("prime_tower_width"))->value;
                 float a = dynamic_cast<const ConfigOptionFloat*>(proj_cfg.option("wipe_tower_rotation_angle"))->value;
 
@@ -2884,6 +2890,8 @@ void GLCanvas3D::reload_scene(bool refresh_immediately, bool force_full_scene_re
                         _set_warning_notification(EWarning::PreviewPrimeTowerOutside, true);
                         x = new_x;
                         y = new_y;
+                        // Persist the correction to config so the next slice uses the valid position
+                        persist_wipe_tower_pos(new_x, new_y);
                     }
 
 
@@ -2906,7 +2914,13 @@ void GLCanvas3D::reload_scene(bool refresh_immediately, bool force_full_scene_re
                         BoundingBoxf3 plate_bbox        = wxGetApp().plater()->get_partplate_list().get_plate(plate_id)->get_build_volume(true);
                         BoundingBox   plate_bbox2d      = BoundingBox(scaled(Vec2f(plate_bbox.min[0], plate_bbox.min[1])), scaled(Vec2f(plate_bbox.max[0], plate_bbox.max[1])));
                         Vec2f         offset            = WipeTower::move_box_inside_box(tower_bottom_bbox, plate_bbox2d, scaled(margin));
-                        int volume_idx_wipe_tower_new = m_volumes.load_real_wipe_tower_preview(1000 + plate_id, x + plate_origin(0), y + plate_origin(1),
+                        // move_box_inside_box returns mm (already unscaled); apply directly.
+                        // If the actual brim polygon is outside bounds, persist the correction to config.
+                        float display_x = x + offset[0];
+                        float display_y = y + offset[1];
+                        if (offset.norm() > float(EPSILON))
+                            persist_wipe_tower_pos(display_x, display_y);
+                        int volume_idx_wipe_tower_new = m_volumes.load_real_wipe_tower_preview(1000 + plate_id, display_x + plate_origin(0), display_y + plate_origin(1),
                                                                                                current_print->wipe_tower_data().wipe_tower_mesh_data->real_wipe_tower_mesh,
                                                                                                current_print->wipe_tower_data().wipe_tower_mesh_data->real_brim_mesh,
                                                                                             true,a,/*!print->is_step_done(psWipeTower)*/ true, m_initialized);

src/slic3r/GUI/PartPlate.cpp

@@ -4074,6 +4074,13 @@ void PartPlateList::set_default_wipe_tower_pos_for_plate(int plate_idx)
         wt_x_opt = ConfigOptionFloat(I3_WIPE_TOWER_DEFAULT_X_POS);
         wt_y_opt = ConfigOptionFloat(I3_WIPE_TOWER_DEFAULT_Y_POS);
     }
+    // Clamp default position to fit within the actual plate dimensions so the wipe tower
+    // doesn't start outside the bed for printers smaller than the hardcoded defaults.
+    const double wt_default_margin  = 2.;
+    const double wt_estimated_width = 60.; // conservative estimate matching prime_tower_width default
+    const double wt_estimated_depth = 20.; // conservative depth estimate
+    wt_x_opt.value = std::max(wt_default_margin, std::min(wt_x_opt.value, m_plate_width  - wt_estimated_width - wt_default_margin));
+    wt_y_opt.value = std::max(wt_default_margin, std::min(wt_y_opt.value, m_plate_depth  - wt_estimated_depth - wt_default_margin));
     dynamic_cast<ConfigOptionFloats *>(proj_cfg.option("wipe_tower_x"))->set_at(&wt_x_opt, plate_idx, 0);
     dynamic_cast<ConfigOptionFloats *>(proj_cfg.option("wipe_tower_y"))->set_at(&wt_y_opt, plate_idx, 0);
 }