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+# TraceCad Architecture
+
+TraceCad is split into small .NET projects with one-way dependencies.
+
+```text
+TraceCad.App    -> TraceCad.Core, TraceCad.Dxf
+TraceCad.Dxf    -> TraceCad.Core
+TraceCad.Vision -> TraceCad.Core
+TraceCad.Core   -> no UI, OpenCV, or DXF package dependencies
+```
+
+## Coordinate Spaces
+
+- Model space: millimetres, used for all stored CAD geometry.
+- View space: screen pixels, used only by the Avalonia canvas.
+- Export space: millimetres, mapped directly to DXF output.
+- Reference space: reserved for calibrated background images in later phases.
+
+## MVP Boundaries
+
+MVP 0.1 intentionally excludes OpenCV, marker detection, automatic tracing, constraints, and dimensions. The first implementation proves deterministic CAD entity creation and DXF export.