stack.sx — precedence as a separate selection layer, not in the rules.
Exclusivity = unordered code pairs; valid-stackings enumerates every legal
subset of applicable promos; best-stacking deterministically picks max total
discount (stable on ties); stacking-by-totalo answers "which legal stacking
yields total D?" backward. Member vs guest falls out of applicable-promos.
Completes Phase 2. Total 99/99 across 6 suites.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
