sweep_polygon creates twisted/self-intersecting mesh in certain cases

[qixuema]

Describe the bug
When using trimesh.creation.sweep_polygon to extrude a polygon along a path, the resulting mesh sometimes contains twisted or self-intersecting faces. This leads to invalid or distorted geometry.

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Code to Reproduce

import numpy as np
import trimesh
from shapely.geometry import Polygon

def _regular_ngon_2d(n_sides: int, radius: float, start_angle: float = 0.0) -> np.ndarray:
    angles = np.linspace(0.0 + start_angle, 2*np.pi + start_angle, n_sides, endpoint=False)
    x = radius * np.cos(angles)
    y = radius * np.sin(angles)
    return np.column_stack([x, y])  # (N,2)

polygon_2d = _regular_ngon_2d(n_sides=5, radius=0.1)

polygon_2d = Polygon(polygon_2d)  # Convert numpy array to shapely Polygon

polyline = np.array([
    [-0.4844,  0.541 ,  0.0815],
    [-0.6675,  0.811 ,  0.4648],
    [-0.5557,  0.9077,  0.627 ],
    [-0.3574,  0.977 ,  0.723 ],
    [-0.1116,  1.001 ,  0.7   ],
    [ 0.1598,  0.973 ,  0.5425],
    [ 0.2084,  0.676 ,  0.1472]]
)

mesh = trimesh.creation.sweep_polygon(polygon_2d, path=polyline, cap=True, connect=False)

mesh.export('sweep_test.obj')

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Expected behavior
The mesh should follow the sweep path smoothly, with faces aligned, and without twisted or self-intersecting geometry.

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Actual behavior

• The generated mesh is visibly twisted and contains distorted faces.
• See attached screenshot for visualization:

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Environment (please complete the following):

• OS: Ubuntu 22.04
• Python version: 3.10
• trimesh version: 4.7.4

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Additional context
It looks like the frame/orientation computation along the sweep path might not be consistent, which causes polygons to flip or rotate unexpectedly.