Cad

interface:
  display_name: "CAD"
  short_description: "Generate and validate CAD artifacts."
  default_prompt: "Use $cad to create, regenerate, inspect, and validate explicit CAD files and selector refs, handing supported outputs to $cad-viewer when available."


# Natural-language CAD brief template

Use this as an internal note-taking scaffold. Do not ask the user to fill it out.

```text
CAD brief:
- Model:
- Task type:
- Units:
- Coordinate convention:
- Overall dimensions:
- Functional features:
- Manufacturing assumptions:
- Positioning/mating requirements:
  - source-level joints or explicit placements:
- STEP source path:
- STEP target path:
- Secondary outputs:
- Validation targets:
- CAD Viewer link target:
- Assumptions:
```


MIT License

Copyright (c) 2026 earthtojake

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
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SOFTWARE.


# build123d modeling patterns

Read this file when writing or repairing build123d Python source.

## Contents

- Modeling objective
- Topology stack
- Source return
- Parameters first
- Coordinate system
- Builder contexts
- Primitives
- Feature operations
- Selection practices
- Assemblies and positioning
- Labels and assemblies
- Common failure modes

## Modeling objective

Create a valid STEP-ready BREP model, not a visual mesh. Prefer closed solids, explicit labels, and stable parametric dimensions.

## Topology stack

Think in this order:

```text
Vertex → Edge → Wire → Face → Shell → Solid → Compound
```

For assemblies, use these repo topology terms consistently:

- **Occurrence**: a placed node in the assembly tree. An occurrence has a parent, transform, path, and user-facing role such as `lid` or `m3_screw:front_left`.
- **Shape**: an exported geometry/body inside an occurrence. Shape rows own topology; faces and edges belong to a shape, and the shape belongs to an occurrence.
- **Face/edge**: selectable topology owned by a shape. Do not assume arbitrary faces or edges have persistent intent labels; inspect them by occurrence, shape, ordinal, surface/curve type, and measured geometry.

When inspecting topology, follow `assembly occurrence -> shape/body -> faces -> edges`. Every face/edge row should be traceable through both `occurrenceId` and `shapeId`.

For normal STEP output, return one of:

- a valid `Solid`
- a compound of valid solids
- a labeled assembly compound

Avoid returning loose wires, open faces, or construction surfaces unless the user explicitly requested them.

## Source return

Generated sources should define:

```python
def gen_step():
    ...
    return step_ready_shape_or_labeled_compound
```

Do not hardcode output paths inside `gen_step()`. The CLI owns output paths.

## Parameters first

Put meaningful dimensions in named variables:

```python
width = 80.0
depth = 50.0
thickness = 6.0
hole_diameter = 4.5
hole_offset_x = 30.0
hole_offset_y = 17.5
```

Avoid burying important numbers inside geometry calls.

## Coordinate system

Declare or comment the convention:

```text
Origin: center of primary part or chosen m