design

name	design
description	Use when you have a brepjs part spec and need to decompose it into an ordered build sequence — choosing which kernel operations to use and in what order, preferring reliable ops and flagging advanced ones (sweeps, lofts, mechanisms) before any code is authored. Runs in the main session.
version	0.1.0

Design the build sequence

Turn a spec (from brepjs:brainstorm) into an ordered list of operations the implementer will author. You decide how to build the part — which ops, what order — not the code itself. Run this in the main session.

Decomposition method

Build outward from a base, in this rough order:

1. Base body — a primitive (box/cylinder/cone/sphere) sized to the main envelope.
2. Additive/subtractive booleans — fuse bosses/ribs on, cut holes/pockets/bores out.
3. Sketched features — when a profile isn't primitive-shaped: 2D sketch → extrude/revolve.
4. Modifiers — fillet/chamfer/shell/offset last, on the consolidated solid.
5. Multiplicity — circularPattern/rectangularPattern for repeats; compound([...]) for multi-part assemblies (no boolean cost, each body stays distinct).

Choose reliable operations

Prefer kernel ops that succeed first-try; reach for advanced ops only when a feature genuinely needs them, and flag those steps as "expect iteration". The canonical reliability tiers live with the implementer (so its clean-room worker always has them):

→ ../implement/references/operation-tiers.md (reliable-first-try vs advanced vs assemblies vs mechanisms).

Key consequences for the sequence:

• Round a corner with fillet over chamfer (chamfer is kernel-fragile).
• Build a prism you'll later fillet/shell from a primitive, not a sketch-extrude, to avoid the Shape3D → ValidSolid lift.
• A hemisphere/dome is a full sphere clipped by a half-space, not a primitive.
• Mechanisms (anything that moves) need a motion-validation step in the plan: sweep the drive parameter and assert no interpenetration — a statically-valid assembly can still jam. See ../implement/references/assemblies-motion.md.

Output

Emit a numbered build sequence, each step naming the operation and its inputs, with advanced/risky steps flagged. In the /brepjs:cad pipeline this is the gate where the orchestrator gets approval; standalone, hand it to brepjs:implement.