Building an exact, deterministic geometry kernel in Rust for an open-source Revit alternative: advice wanted on approach and strategy

[u/heldloosly]

We're a small co-op building Spare Kit, an open-source (MPL-2.0) geometry kernel in Rust, to power a Revit/CAD alternative that runs natively and in the browser (WASM). Much of the code is written by AI agents working through a mapped plan, with strict testing as the safeguard.

The approach:

- Integer grid coordinates (±2^40 steps) with exact predicates (generated filters, exact integer fallback), so topology decisions never depend on float rounding.

- Flat geometry stays plane-based with implicit points (EMBER style), so booleans never drift; curved geometry is computed with certified error bounds, with only the decisions kept exact.

- Bit-identical results on every target (x86-64, ARM, wasm32), as a tested guarantee.

- Verification: big-integer oracles, fuzzing (bolero/Kani), golden digests, instruction-count performance gates.

The strategy: a mapped board of about 480 pieces in 13 phases. The first real milestone is a wall with 300 openings cut exactly, saved, reopened and replayed bit for bit everywhere, before any curved work starts. We're early: number layer, exact predicates, implicit points and symbolic perturbation so far.

Advice we'd value on anything, especially:

1. The seam between exact flat geometry and certified curved geometry: seen it break, or a better way?

2. Is the scope or the strategy wrong? What would you cut or reorder?

3. Existing crates or projects we should build on instead of writing our own?

4. Is our testing bar overkill or missing something?

5. Anything else you'd tell someone starting a kernel like this.

Architecture: https://github.com/spareware-co-op/spareware/blob/main/projects/engines/geometry/ARCHITECTURE.md

[u/AlternativePrior1920]

Why not copy-paste those question to your favorite LLM if you're so inclined already?