fix: clear destroyed-NPC state; use true EV in trade scoring (review)

src/sim/npc.js

@@ -70,7 +70,7 @@ export function planNpc(world, npc) {
       if (sellP <= buyP * 1.15) continue; // demand a margin over price noise
       const qty = Math.min(npc.capacity, Math.floor(npc.credits / buyP), Math.floor(origin.stock[good] * 0.5));
       if (qty < 1) continue;
-      const profit = (sellP - buyP) * qty * survival;
+      const profit = (sellP * survival - buyP) * qty; // EV: buy cost is sunk even if cargo is lost
       if (profit <= 0) continue;
       const days = Math.max(LOCAL_HOP_DAYS, route.days);
       const noise = 0.9 + 0.2 * rollFor(npc.seed, `${planId}:noise:${dest.id}:${good}`);
@@ -111,6 +111,8 @@ export function onNpcArrive(world, { npcId, planId }) {
   if (plan.finalOutcome === 'destroyed') {
     npc.alive = false;
     npc.plan = null;
+    npc.cargo = null;
+    npc.state = 'destroyed';
     world.stats.npcDestroyed++;
     return;
   }