Record an M600 color-change boundary (DD-009 D2, #147). Position is absolute; stored origin-relative.
Register an object; returns its 1-based index for use in SegmentInput.object.
Record a retraction/unretraction event (DD-009 D1, #148). Position is absolute; stored origin-relative.
Accumulates segments and produces a canonical ToolpathIR.
The builder accumulates into plain number arrays and converts to typed arrays in ToolpathIRBuilder.finalize. The canonical IR it returns is already the compact, transferable typed-array contract from DD-001; E2 (the worker parser) will additionally write directly into growable typed buffers to avoid the intermediate arrays.