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docs/architecture.md

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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.

docs/dxf-export.md

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+# DXF Export
+
+DXF is an export format, not TraceCad's internal document format.
+
+The MVP exporter uses `netDxf` behind `IDxfExporter` so the implementation can be replaced without changing core or UI code.
+
+## Current Mapping
+
+| TraceCad entity | DXF entity |
+| --- | --- |
+| `LineEntity` | `LINE` |
+| `CircleEntity` | `CIRCLE` |
+| `ArcEntity` | `ARC` |
+
+All exported geometry is written in millimetres. Non-exportable layers such as `CONSTRUCTION`, `REFERENCE`, `DIMENSIONS`, and `DEBUG` are skipped by default.

docs/mvp.md

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+# MVP 0.1
+
+MVP 0.1 focuses on the editor core:
+
+- Start the Avalonia desktop app.
+- Pan and zoom a millimetre canvas.
+- Draw lines from two points.
+- Draw circles from three circumference points.
+- Draw arcs from start, through, and end points.
+- Select and delete entities.
+- Undo and redo document mutations.
+- Save and load the native JSON project format.
+- Export LINE, CIRCLE, and ARC entities to DXF.
+
+MVP 0.2 adds the manual reference-image layer:
+
+- Import a raster image as a locked background reference.
+- Display the reference below CAD entities.
+- Adjust opacity independently of geometry.
+- Lock and unlock the reference.
+- Edit reference X/Y origin, scale, and rotation manually.
+- Save and reload reference metadata in the native JSON project file.
+
+Deferred work:
+
+- Calibration sheet generation.
+- OpenCV marker detection.
+- Assisted fitting tools.
+- Constraint and dimension systems.