When a constant profile's half-width reaches the local radius of curvature, the smooth inner offset crosses the centre and the non-zero fill leaves a hole. Cut through the centre at those samples; the cut is inside the painted stroke. Varying profiles keep the offset because their crossings can be real caustics, where a cut would show as a slit. Regression test: a radius-5 circle with a 30 pt stroke contains its centre.
Adam
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