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-engine/src/systems/infrastructureSystem.ts

@@ -358,22 +358,19 @@ function processNetworkTick(
   repairSpeedBonus: number,
   hotStandbyTicks: number,
   redundancyBonus: number,
-): { switchRepairCosts: number; notifications: TickNotification[]; dirty: boolean } {
+): { switchRepairCosts: number; notifications: TickNotification[]; dirtyDCs: Set<string> } {
   const notifications: TickNotification[] = [];
   let switchRepairCosts = 0;
-  let dirty = false;
+  const dirtyDCs = new Set<string>();
 
   const healthyByTier: Partial<Record<SwitchTier, NetworkSwitch[]>> = {};
   const repairing: NetworkSwitch[] = [];
-  const failed: NetworkSwitch[] = [];
 
   for (const sw of Object.values(registry)) {
     if (sw.status === 'healthy') {
       (healthyByTier[sw.tier] ??= []).push(sw);
     } else if (sw.status === 'repairing') {
       repairing.push(sw);
-    } else if (sw.status === 'failed') {
-      failed.push(sw);
     }
   }
 
@@ -397,9 +394,9 @@ function processNetworkTick(
         sw.repairProgress = 0;
         sw.repairTotal = repairTime;
         newlyFailed.push(sw);
+        if (sw.dcId) dirtyDCs.add(sw.dcId);
         switchRepairCosts += SWITCH_TIER_CONFIGS[tier].baseCost * SWITCH_REPAIR_COST_FRACTION;
       }
-      dirty = true;
     }
   }
 
@@ -409,13 +406,14 @@ function processNetworkTick(
       sw.status = 'healthy';
       sw.repairProgress = 0;
       sw.repairTotal = 0;
-      dirty = true;
+      if (sw.dcId) dirtyDCs.add(sw.dcId);
     }
   }
 
-  if (dirty) {
+  if (dirtyDCs.size > 0) {
     for (const sw of Object.values(registry)) {
       if (sw.uplinkIds.length === 0) continue;
+      if (sw.dcId && !dirtyDCs.has(sw.dcId)) continue;
       let active = 0;
       for (const upId of sw.uplinkIds) {
         if (registry[upId]?.status === 'healthy') active++;
@@ -435,7 +433,7 @@ function processNetworkTick(
     }
   }
 
-  return { switchRepairCosts, notifications, dirty };
+  return { switchRepairCosts, notifications, dirtyDCs };
 }
 
 // --- Interconnect Training Multiplier ---
@@ -478,16 +476,13 @@ export function processInfrastructure(state: GameState, researchBonuses?: Resear
   const hotStandbyTicks = state.research.completedResearch.includes('network-hot-standby') ? 5 : 0;
   const redundancyBonus = state.research.completedResearch.includes('network-redundancy') ? 1 : 0;
 
-  // Clone switch registry for mutable operations this tick
-  const registry: Record<string, NetworkSwitch> = {};
-  for (const [id, sw] of Object.entries(state.infrastructure.switchRegistry)) {
-    registry[id] = { ...sw, uplinkIds: [...sw.uplinkIds], downlinkIds: [...sw.downlinkIds] };
-  }
+  // Mutate registry in-place — infrastructure returns a new state anyway
+  const registry = state.infrastructure.switchRegistry;
 
   // Process network failures/repairs globally
   const netResult = processNetworkTick(registry, networkResearchBonus, opsEff, repairSpeedBonus, hotStandbyTicks, redundancyBonus);
   repairCosts += netResult.switchRepairCosts;
-  notifications.push(...netResult.notifications);
+  if (netResult.notifications.length > 0) notifications.push(...netResult.notifications);
 
   let totalFlops = 0;
   let totalTrainingFlops = 0;
@@ -671,8 +666,8 @@ export function processInfrastructure(state: GameState, researchBonuses?: Resear
 
         repairCosts += dcRepairCosts;
 
-        // Recompute DC network summary after failures/repairs
-        if (netResult.dirty && networkSummary.switchIds.length > 0) {
+        // Recompute DC network summary after failures/repairs (only if this DC's switches changed)
+        if (netResult.dirtyDCs.has(dc.id) && networkSummary.switchIds.length > 0) {
           networkSummary = buildDCSummary(
             networkSummary.switchIds, networkSummary.networkRackCount, registry,
           );