step 10.14: done

docs/DECISIONS.md

@@ -37,6 +37,11 @@ Format:
 - Decision: Each round, both attack; faster first; hero wins speed ties; a kill ends the round.
 - Consequences: Round log has up to 2 entries per round (max 40). Win rates need re-tuning (see STATUS issue 1).
 
+## D-022: Material sell prices use item-level formula
+- Context: BALANCE.md says materials sell at `common 2×level, uncommon 4×level, rare 8×level` — but "level" was ambiguous (hero level vs item level). The code used `defaultRate * heroLevel / itemMinLevel`, making high-level heroes overpay and low-level heroes underpay for high-level materials.
+- Decision: Use `materialSellPrice(rarity, itemMinLevel)` from `src/game/rewards.js` — price depends on the ITEM's level, not the hero's. BALANCE.md table corrected to match the formula (e.g., Drake Scale: 90g → 112g).
+- Consequences: Existing shop tests that asserted hero-level prices updated; material sell prices are now consistent regardless of hero level.
+
 ## D-005: Equipment stats are counted once in derived stats
 - Context: maxHp added equipment VIT twice (once in totalVit, once as a separate term).
 - Decision: `calcDerived` in `src/game/stats.js` is the ONLY derived-stat formula; combat and services call it.