OCC: Broken body with helix & pad

### Problem description

Related to : [#32486](https://github.com/FreeCAD/FreeCAD/issues/32486)

I tried to create the threads first using additive helix.
Then added fillet. Which worked fine.
Then I added an extrude to fill the center cavity.
But the solid appears broken.

Refer image below

### Workbench affected?

Part Design

### Steps to reproduce

Open & inspect the TestScrew.FCStd

[TestScrew2.zip](https://github.com/user-attachments/files/31927497/TestScrew2.zip)

### Expected behavior

N/A

### Actual behavior

N/A

### Development version About Info (in Safe Mode)

```shell
OS: Windows 10 build 19045
Architecture: x86_64
Version: 1.1.3.20260725 (Git shallow)
Build date: 2026/07/25 04:52:02
Build type: Release
Branch: grafted,grafted
Hash: 145529fe741292ff0b3977a01195bf0247425794
Python 3.11.14, Qt 6.8.3, Coin 4.0.3, Vtk 9.3.1, boost 1_86, Eigen3 3.4.0, PySide 6.8.3
shiboken 6.8.3, xerces-c 3.3.0, IfcOpenShell 0.8.4, OCC 7.8.1
Locale: English/India (en_IN)
Navigation Style/Orbit Style/Rotation Mode: SiemensNX/Rounded Arcball/Window center
Stylesheet/Theme/QtStyle: FreeCAD.qss/FreeCAD Dark/
Logical DPI/Physical DPI/Pixel Ratio: 96/102.406/1
```

### Last known good version (optional)

```shell

```

Open the attached TestScrew2.zip in FreeCAD's Part Design workbench and inspect the additive helix, fillet, and extrude sequence. Reproduce the broken solid and compare it with the supplied image; the issue provides no expected behavior, so confirm the intended result before considering the investigation complete.

Written by the indexing model from the issue text.