Port nebula_app's builtin_font coverage (box drawing, block elements, legacy sextants/blocks, Powerline separators) from pixel rasterization to renderer-agnostic fill primitives: axis-aligned rects plus convex polygons, snapped to device pixels so strokes stay crisp and join seamlessly across cells. RenderSnapshot::capture now routes these cells to box_glyphs instead of text segments - the typography engine never touches them, which roots out the box-line misalignment CJK fonts cause. The GPUI element consumes the primitives via paint_quad/paint_path (cursor inversion rules unchanged). Known deltas vs the legacy rasterizer: narrow-cell Powerline tips clip instead of falling back to the font, and shade blocks use alpha 64/128/192. Engine tests: 202 passing (11 new).
kuddev
30d5279d9f