feat: scaffold mvp shell and content runtime

js/gameplay/difficulty/evaluate-board.js

@@ -0,0 +1,29 @@
+import { getClickablePieces } from './overlap-graph.js'
+
+function clamp(value, min, max) {
+  return Math.min(max, Math.max(min, value))
+}
+
+export function evaluateBoard(boardState, levelPreset) {
+  const pieces = (boardState.pieces ?? []).filter((piece) => !piece.removed)
+  const clickablePieces = getClickablePieces(boardState)
+  const totalPieces = pieces.length
+  const initialClickableRatio = totalPieces === 0 ? 0 : clickablePieces.length / totalPieces
+  const targetPassRate = levelPreset?.targetPassRate ?? 0.75
+  const visibilityBonus = (initialClickableRatio - 0.3) * 0.35
+  const densityPenalty = levelPreset?.density === 'high' ? 0.05 : levelPreset?.density === 'medium_high' ? 0.03 : 0
+  const toolFreePassRate = clamp(targetPassRate + visibilityBonus - densityPenalty, 0.45, 0.99)
+  const toolAssistPassRate = clamp(toolFreePassRate + 0.12, toolFreePassRate, 1)
+  const avgTurnsToFinish = totalPieces / 1.2
+
+  return {
+    totalPieces,
+    initialClickableRatio,
+    simulatedPassRate: toolFreePassRate,
+    avgTurnsToFinish,
+    toolFreePassRate,
+    toolAssistPassRate,
+  }
+}
+
+export default evaluateBoard