Add game-simulation package with multi-run balance testing, fix stalled-pipeline trap

Adds a full simulation harness (game-simulation package) with greedy/random strategies,
36-metric diagnostics, multi-run orchestration via child processes, and a statistical
interpreter. Includes 2.3x engine performance optimizations (research bonus caching,
per-DC dirty tracking, reduced allocations in tick pipeline, single-pass loops).

Fixes a critical balance bug where training pipelines stalled on insufficient VRAM would
permanently block training slots — the engine never re-checked stalled pipelines, and the
greedy strategy didn't pre-check VRAM requirements. This caused 20-25% of seeds to get
stuck in Scale-up era. All three fixes (engine un-stalling, strategy VRAM pre-check,
stalled pipeline cancellation) bring pass rate from 75% to 100% across 20 random seeds.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/game-simulation/src/analysis/deadZones.ts

@@ -0,0 +1,79 @@
+import type { GameState, RackSkuId } from '@ai-tycoon/shared';
+import { RACK_SKU_CONFIGS } from '@ai-tycoon/shared';
+import type { SimulationMetrics } from '../strategies/types';
+
+export interface DeadZone {
+  startTick: number;
+  endTick: number;
+  durationTicks: number;
+  description: string;
+}
+
+function getCheapestSkuCost(state: GameState): number {
+  const era = state.meta.currentEra;
+  const eraOrder = ['startup', 'scaleup', 'bigtech', 'agi'];
+  const eraIdx = eraOrder.indexOf(era);
+
+  let cheapest = Infinity;
+  for (const [, sku] of Object.entries(RACK_SKU_CONFIGS)) {
+    if (eraOrder.indexOf(sku.era) <= eraIdx) {
+      cheapest = Math.min(cheapest, sku.baseCost);
+    }
+  }
+  return cheapest === Infinity ? 100_000 : cheapest;
+}
+
+export function detectDeadZones(
+  metrics: SimulationMetrics[],
+  cheapestSkuCost: number,
+  windowSize = 10,
+  revenueTolerance = 0.02,
+  capabilityTolerance = 0.02,
+): DeadZone[] {
+  const zones: DeadZone[] = [];
+  let zoneStart: number | null = null;
+
+  for (let i = windowSize; i < metrics.length; i++) {
+    const current = metrics[i];
+    const past = metrics[i - windowSize];
+
+    const revFlat = past.revenue > 0
+      ? Math.abs(current.revenue - past.revenue) / past.revenue < revenueTolerance
+      : current.revenue === 0;
+
+    const capFlat = past.bestModelCapability > 0
+      ? Math.abs(current.bestModelCapability - past.bestModelCapability) / past.bestModelCapability < capabilityTolerance
+      : current.bestModelCapability === 0;
+
+    const isStuck = revFlat && capFlat && current.money < cheapestSkuCost * 2;
+
+    if (isStuck) {
+      if (zoneStart === null) zoneStart = past.tick;
+    } else {
+      if (zoneStart !== null) {
+        const endTick = metrics[i - 1].tick;
+        zones.push({
+          startTick: zoneStart,
+          endTick,
+          durationTicks: endTick - zoneStart,
+          description: 'revenue flat, no affordable upgrades',
+        });
+        zoneStart = null;
+      }
+    }
+  }
+
+  if (zoneStart !== null) {
+    const endTick = metrics[metrics.length - 1].tick;
+    zones.push({
+      startTick: zoneStart,
+      endTick,
+      durationTicks: endTick - zoneStart,
+      description: 'revenue flat, no affordable upgrades (ongoing)',
+    });
+  }
+
+  return zones;
+}
+
+export { getCheapestSkuCost };