andymai/brepjs/design

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`.