| 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:
- Base body — a primitive (
box/cylinder/cone/sphere) sized to the main envelope.
- Additive/subtractive booleans —
fuse bosses/ribs on, cut holes/pockets/bores out.
- Sketched features — when a profile isn't primitive-shaped: 2D sketch →
extrude/revolve.
- Modifiers —
fillet/chamfer/shell/offset last, on the consolidated solid.
- 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.
