instructions.py: build_steps(scene, plan) emits an ordered, DETERMINISTIC step
list from the CutPlan + scene — gather stock, cut to size (per cut layout), mark
& cut joinery, sand, dry-fit/glue/fasten (per connection), finish. Every number
and part name comes from the model. polish_prompt() asks the AI to rephrase into
friendly prose while forbidding any change to measurements.
BOM window gains an Instructions tab: shows the deterministic steps immediately,
"Rewrite in plain English (AI)" runs claude in a background thread to polish, and
Print.
111 tests pass (steps cover phases, carry real data, prompt guards numbers).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
