diff --git a/server/src/game/GameLoop.ts b/server/src/game/GameLoop.ts
index 6b12ccb..95a322a 100644
--- a/server/src/game/GameLoop.ts
+++ b/server/src/game/GameLoop.ts
@@ -77,6 +77,7 @@ export class GameLoop {
       this.narrationService,
       this.eventMemoryService,
       (summary) => this.onInventionCreated?.(summary),
+      () => this.getDayNumber(),
     );
     this.desireGeneratorSystem = createDesireGeneratorSystem(this.llmService, this.eventMemoryService);
 
diff --git a/server/src/systems/inventionSystem.ts b/server/src/systems/inventionSystem.ts
index c955d3e..0a3087d 100644
--- a/server/src/systems/inventionSystem.ts
+++ b/server/src/systems/inventionSystem.ts
@@ -11,7 +11,6 @@ import { parseInventionResponse } from '../industry/inventionParser.js';
 import { validateInvention } from '../industry/inventionValidator.js';
 import { registerInvention } from '../industry/inventionRegistrar.js';
 import { industryConfig } from '../config/industryConfig.js';
-import { ENERGY_DECAY_PER_TICK, DAY_NIGHT_RATIO } from '@dflike/shared';
 import { logLlmDebug } from '../llm/llmDebugLog.js';
 
 export interface InventionSystem {
@@ -23,6 +22,7 @@ export function createInventionSystem(
   narrationService: NarrationService,
   eventMemoryService: EventMemoryService,
   onInventionCreated?: (summary: InventionSummary) => void,
+  getDayNumber?: () => number,
 ): InventionSystem {
   // Track in-flight requests to avoid duplicates
   const pendingEntities = new Set<EntityId>();
@@ -145,11 +145,7 @@ export function createInventionSystem(
           }
           pendingItemIds.add(validation.itemId!);
 
-          // Compute current day
-          const dayTicks = 100 / ENERGY_DECAY_PER_TICK;
-          const nightTicks = dayTicks / DAY_NIGHT_RATIO;
-          const cycleTicks = Math.round(dayTicks + nightTicks);
-          const day = Math.floor(tick / cycleTicks) + 1;
+          const day = getDayNumber ? getDayNumber() : 1;
 
           console.log(`[Invention] SUCCESS npc=${name} (${entityId}) invented "${parsed.name}" (${validation.itemId}) cat=${parsed.category}`);