WORK IN PROGRESS: MANY FEATURES MAY BE BROKEN. Bug reports, test results from real FreeCAD, Fusion and slicers, other CAD exporters and pull requests are welcome.

• Open an issue first for anything big. Use the bug-report form.
• By contributing you agree your contribution is licensed under the same PolyForm Noncommercial License 1.0.0 as the project, with the Required Notice Copyright Matthew Armstrong (https://github.com/The-Dorkknight) kept in every source file header.
• Only contribute code you have the right to contribute. Don't paste in code from projects with incompatible licences.
• src/hstl.py is copied into both plug-in folders (they must run on their own inside FreeCAD and Fusion). Change it in src/ and copy it over; python tests/test_hstl.py checks the three copies match.
• Two rules for format changes: a labelled file must stay byte-identical in its triangles to its plain twin, and labels must stay hints that a reader checks. Raise the format version if the bit layout or header changes.
• Before a PR, run python tests/test_hstl.py and python tests/test_install.py, and python tests/test_hardpoint_cad.py if you touched the format or an exporter. DESIGN_NOTES.md has the background and a list of open work.