Split mega-files: vcad-kernel-wasm/src/lib.rs (5912 lines) and vcad-ir/src/lib.rs (1969 lines)

[ecto]

Problem

Two source files have organically grown to where they actively hurt navigation, incremental compile times, and reviewability:

• crates/vcad-kernel-wasm/src/lib.rs — 5912 lines. All #[wasm_bindgen] surface in one file: Solid impl, primitives, sweeps, drafting, slicer cost, raytrace, embroidery, the new DFM bindings I just added. cargo build recompiles the whole file on any change, which compounds the wasm-pack bundle time.
• crates/vcad-ir/src/lib.rs — 1969 lines. CsgOp enum, Node, MaterialDef, SceneEntry, EnvironmentPreset, Document, createDocument, helpers, tests — all in one file. Adding a new CsgOp variant is awkward when the enum is in the middle of a 2000-line file.

Proposed split

vcad-kernel-wasm

src/
  lib.rs              # crate doc + init + #[wasm_bindgen(start)] + re-exports
  primitives.rs       # Solid::cube/cylinder/sphere/cone + bbox + volume + COM
  sweeps.rs           # extrude/revolve/sweep_line/sweep_helix/loft
  booleans.rs         # union/difference/intersection
  transforms.rs       # translate/rotate/scale/mirror
  features.rs         # fillet/chamfer/shell/pattern
  drafting.rs         # section_mesh / projections / hatch
  cost.rs             # estimatePrintCost + estimate_cost_for_process (the new DFM-era binding)
  dfm.rs              # run_dfm_on_brep_json + get_default_dfm_pack + Solid::runDfm
  raytrace.rs         # render bindings
  embroidery.rs
  ecad.rs

The Solid struct stays in lib.rs; impl Solid blocks split across files (Rust allows multiple impl blocks).

vcad-ir

src/
  lib.rs              # crate doc + re-exports
  op.rs               # CsgOp enum + tool_schema attrs
  node.rs             # Node, NodeId
  scene.rs            # SceneEntry, EnvironmentPreset, scene settings
  material.rs         # MaterialDef
  document.rs         # Document, createDocument, toJson/fromJson, toVCode/fromVCode
  sketch.rs           # SketchSegment2D and friends
  vcode.rs            # already split out
  vec3.rs             # already split out

Why now

• The DFM PR added another ~150 lines to vcad-kernel-wasm/src/lib.rs. The next feature will add another 100. There's no natural stopping point.
• Touching vcad-ir/src/lib.rs for any IR change recompiles every TS workspace package via the codegen path.
• Reviewers can't grok diffs in either file without context.

Acceptance criteria

• Both files drop below 500 lines each (re-exports + crate-level docs only).
• cargo build --workspace and cargo test --workspace pass unchanged.
• cargo clippy --workspace -- -D warnings clean.
• wasm-pack build produces a binary with the same exports (verified by diffing vcad_kernel_wasm.d.ts).
• No public API changes — this is a pure mechanical split.

References

• crates/vcad-kernel-wasm/src/lib.rs — 5912 lines
• crates/vcad-ir/src/lib.rs — 1969 lines
• For the WASM split, the existing crates/vcad-kernel-wasm/src/{document_engine, keybindings, sketch_session}.rs are precedent for sibling modules