Implement

Hard rules

• Import every function you call. No globals — every op is a named export from 'brepjs'. A used-but-unimported symbol is TS2304: Cannot find name and fails --check before geometry runs (the #1 first-attempt failure). Re-scan the body before finishing.
• Transforms are free functions, shape-first — translate(shape, [x,y,z]), rotate(shape, deg, { axis }), mirror, scale (angles in degrees), the same shape-first form as booleans. They are NOT methods: shape.translate(...) is TS2339: Property 'translate' does not exist. Placing assembly parts needs these even when the brief doesn't shout "transform". (references/transforms.md.)
• Unwrap Results. Booleans and measureVolume/measureArea return Result: unwrap(cut(...)) and check the Err branch before chaining. TS2322: Result<X> is not assignable to X (on an assignment/return) — or TS2345 when you feed an un-unwrapped Result straight into another op's argument (e.g. fuse(a, cut(b, c))) — means an op (cut/fuse/fillet/chamfer/shell/…) was used without unwrap(). Unwrap at every step, including the final return — a Result default export (export default cut(...)) slips past verify (it auto-unwraps a Result default export, so --check is green) but renders nothing in a viewer/mesh path. Always unwrap() the returned shape.
• fuse welds only where solids overlap. Bodies merely touching on a coplanar face/ring may return a loose Compound (ok:true, not one watertight solid). Overlap the operands + fuseAll(shapes, { unsafe: true }) to weld; use compound for a distinct-bodies assembly. For MANY operands (a grille, a stud grid, a space frame), fuseAll unsafe routinely leaves a loose N-solid compound even with overlap — fold with a pairwise fuse() reduce over real overlaps and confirm getSolids(part).length === 1. (references/booleans.md.) But a Compound result is NOT a failure to chase: even genuinely overlapping operands often fuse to shapeType:Compound (ok:true, correct geometry) rather than a single Solid — and that's fine, because shapeType is report-only/non-authorable and bounds/volume/validity still pass. Don't burn attempts trying to force a Solid; only do so (and then only worry) when a downstream fillet/shell/offset needs a ValidSolid (next rule). The report's notes flags a multi-body Compound and its solid count — if a part you meant as ONE piece comes back as N bodies, the weld failed (overlap + fuseAll unsafe); a count matching a deliberate assembly is fine.
• fillet/chamfer/shell/offset need a ValidSolid. Primitives already are one and booleans preserve it, so a primitive-rooted chain feeds them directly. A shape from a 2D-sketch .extrude()/.revolve() (or loft/sweep) is typed Shape3D; passing it to these ops is TS2345. Lift in two steps: if (!isSolid(x)) throw …; const solid = unwrap(validSolid(x));. Or build the prism from a primitive when you know you'll fillet/shell it. (references/modifiers.md.)
• A loose-Compound boolean can't be lifted to ValidSolid — fix the boolean, don't lift. When fuse/fuseAll only touch (don't overlap) they return a Compound (ok:true), and isSolid returns false on it (shapeType()==='compound', not 'solid' — src/core/shapeTypes.ts:248). There is no lift from a multi-body Compound to a ValidSolid: validSolid() needs one Solid, so if (!isSolid(x)) throw … just throws, and feeding the Compound onward KERNEL_FAILEDs. Make the operands actually overlap and fuseAll(shapes, { unsafe: true }) so the weld yields a single solid first, then fillet/shell. (references/booleans.md.)
• Select edges/faces; don't fillet/chamfer everything. fillet(solid, radius) with no edge list rounds EVERY edge and frequently FILLET_FAILEDs. Pass edgeFinder().inDirection('Z').findAll(solid). inDirection matches BOTH ± orientations; discriminate by position with .when(f => getBounds(f).zMax > t) (getBounds is its own import). Finders take a direction ('X'/'Y'/'Z'/Vec3), never a plane: a top face is faceFinder().inDirection('Z'); parallelTo('XY') fails --check — use 'Z'. (references/modifiers.md.)
• chamfer is kernel-fragile. CHAMFER_FAILED is common even with a correct edge list. Prefer fillet, model the bevel additively (cut with an angled tool), or drop it. Re-running the same chamfer rarely helps.
• A through hole/slot/mortise needs a tool proud of BOTH faces. Size the cutting cylinder/box LONGER than the body and place it so it pokes out each end (e.g. height = wall + 2, positioned past both faces) — a tool flush with or short of a face leaves a blind pocket, not a through feature, and --check can't catch it (the part is still valid). The brief word "through" (or "bore", "passage") is the cue. Confirm it actually passes through with the section/xray view, not just the exterior.
• revolve angle is RADIANS (Math.PI * 2 = full turn). Build a revolve profile with polygon(points3D), not draw().close().sketchOnPlane('XZ').face() (fails --check). (references/sketching-2d.md.)
• box(width, depth, height) — depth is Y, height is Z, mm. at sets the geometric CENTER: bare box(w,d,h) is corner-at-origin, { centered: true } centers on origin, { at:[x,y,z] } centers there. cylinder/cone at is the base center; sphere at is its center.
• No half-sphere primitive: clip a full sphere to a half-space with intersect (a box over the half you want). Fusing a whole sphere bulges past a cap face. See the dome-cap example.
• Pattern angles are DEGREES (circularPattern/rectangularPattern fullAngle), unlike revolve (radians). Check the unit per op.
• Parts may be async: export default async () => {…} is awaited — await loadFont(...) (required before any sketchText/drawText) or await importSTEP(...). --check type-checks Node built-ins, so a part may import { readFile } from 'node:fs/promises'.
• Author in ESM (the tool's default) so the kernel loads.

Reference index (load only what the task needs)

references/getting-started.md · primitives.md · sketching-2d.md · booleans.md · modifiers.md · transforms.md · measurement-validation.md · assemblies-motion.md · operation-tiers.md. Maker recipes: fdm-conventions.md · mechanical-joints.md · gridfinity.md · gears.md · threads.md · airfoils.md (fans/props/impellers/vanes). Buildings/BIM/IFC: families-bim.md (declarative components → viewport meshes + IFC export). Backstop: any symbol not covered → reference/llms-full.txt (every export with signatures), bundled in the package.

Examples index (read the closest before authoring)

Each is a complete examples/<name>.brep.ts + <name>.expected.json baseline.

• Primitives + booleans: mounting-bracket · flanged-coupler · transform-bracket · dome-cap.
• 2D sketch → solid: extruded-bracket · revolved-pulley · swept-gasket.
• Modifiers: rounded-block (fillet) · chamfered-block (API shape only; chamfer is fragile) · hollow-enclosure (shelled).
• Mechanical: spur-gear (polygon→extrude, BOSL2-faithful) · threaded-rod (loft sections).
• Gridfinity: gridfinity-baseplate · gridfinity-bin · gridfinity-divider.