BRep-aware diff & merge ("git for CAD")

[ecto]

Background

vcad-crdt merges the feature DAG at parameter granularity (LWW HLCs) — no geometric awareness. Two branches that are parametrically different but geometrically equal look like conflicts; concurrent adds that geometrically overlap aren't detected. Uniquely aligned with vcad's AI-native identity and already ~70% built.

Deliverables

• New crates/vcad-kernel-diff/:
  • diff_brep(a, b) -> BRepDiff — added/removed/modified faces with volume + surface-area deltas
  • Topology-aware matching (persistent IDs from the associative-drawings issue, Hausdorff fallback)
• App: side-by-side compare view with coloured overlay (red=removed, green=added, yellow=changed)
• Use diff as merge-conflict detector in vcad-crdt
• Hook into Supabase document_versions — "Compare with v12" button

Use cases

PR reviews on .vcad, Supabase version-history visual compare, AI edit validation.

Reference. NX "compare bodies", Onshape "compare workspaces".