Phase 0: CutPlan model (deterministic shop-output artifact)
Adds SHOP_PACKET_PLAN.md (living plan) and cutplan.py: ShopSettings, CutItem,
StockPiece, Placement, WasteRegion, CutPlan — plain dataclasses, JSON-serializable,
stable ids throughout. build_cut_plan(scene, settings, strategy) packs lumber
(first-fit-decreasing, kerf-aware) and plywood (shelf) into the model with waste
regions and a detailed score {strategy, stock_count, waste_area, reusable_offcuts,
yield_pct, warnings}. validate_cut_plan checks bounds/overlap/kerf/placed-or-warned.
Old APIs kept as thin wrappers over build_cut_plan: layout.nest_lumber/nest_plywood/
stock_counts/waste_summary (so existing tests/UI/cutlist.shopping keep working).
The BOM window's Cut Layout tab now renders directly from the CutPlan (score line,
stick/sheet placements, waste, warnings).
104 tests pass incl. kerf, tenon-extended items, oversize warnings, JSON roundtrip,
validation, custom settings. UI says "Try another arrangement", not "optimal".
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
rob
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