share the world shapes both views (game and balancing) draw identically

docs/architecture.md

@@ -371,6 +371,8 @@ The renderer iterates only entities and tiles whose world X lies within the visi
 
 Shapes are hardcoded in the renderer — a building is a rectangle per footprint tile, a ship is an oriented arrow/triangle, a belt item is a 10×10 square, scrap is a small circle, a beam is a line. These structural choices live in the `draw<X>(painter, entity)` functions of the UI and are not expected to change frequently.
 
+The few shapes the game view and the balancing tool's arena view draw *identically* — the ship body, the health bar, the debris marker, the sensor-range circle — live in `ui/WorldPrimitives` as free functions over explicit values. The arena exists to eyeball combat, so it only works while a ship there looks like a ship in the game; keeping these in one place means a retuned ship shape cannot silently stop applying to the tool that measures it. The balancing target does not link the `ui` library, so it compiles that file into itself, the same way it already does for `VisualsLoader` and `ShipStatsPanel` (see `balancing/CMakeLists.txt`). Everything the two views draw differently — selection highlights, beams, target lines, and all of the factory — stays with each view; the shared set is deliberately not grown beyond shapes that are genuinely the same.
+
 Colors, outline widths, glyph text, and tile tints live in a separate config file, `visuals.toml`, loaded once by the UI at startup using the same pattern and lifetime as the sim config files (see Config Loading). The file is UI-scoped: the sim does not read it and does not depend on it.
 
 Sketch of `visuals.toml`: