Character Rotation turned a glyph's baseline shift and scaling with the glyph, and the Skew path effect slants a glyph's height away from the path's normal, so the x-height guide moved off the glyphs. Each positioned glyph now carries the transform that removes its Character Rotation (PositionedGlyph::unturned), and the guide goes through the glyph's x-height point placed without it, measured across the baseline. Snap to Glyph also takes Smart Guides being on in the tools, as View › Snap to Glyph already does in the engine.
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