diff --git a/server/src/systems/__tests__/systems.test.ts b/server/src/systems/__tests__/systems.test.ts
index 12ea214..9f04707 100644
--- a/server/src/systems/__tests__/systems.test.ts
+++ b/server/src/systems/__tests__/systems.test.ts
@@ -388,6 +388,84 @@ describe('npcBrainSystem', () => {
     const brain = world.getComponent<NPCBrain>(e, 'npcBrain')!;
     expect(brain.currentGoal).toBe('drink');
   });
+
+  // Daytime nap tests
+  it('wakes from daytime nap at calculated energy target', () => {
+    const world = new World();
+    const map = new GameMap(10, 10);
+    const e = createNPC(world, 5, 5, 80, 61);
+    addStats(world, e, { constitution: 10 });
+    const brain = world.getComponent<NPCBrain>(e, 'npcBrain')!;
+    brain.currentGoal = 'sleep';
+    npcBrainSystem(world, map, 0.5, undefined, rc);
+    expect(brain.currentGoal).not.toBe('sleep');
+  });
+
+  it('stays asleep during daytime nap when energy below target', () => {
+    const world = new World();
+    const map = new GameMap(10, 10);
+    const e = createNPC(world, 5, 5, 80, 55);
+    addStats(world, e, { constitution: 10 });
+    const brain = world.getComponent<NPCBrain>(e, 'npcBrain')!;
+    brain.currentGoal = 'sleep';
+    npcBrainSystem(world, map, 0.5, undefined, rc);
+    expect(brain.currentGoal).toBe('sleep');
+  });
+
+  it('uses full sleep when nap target below voluntary threshold (near nightfall)', () => {
+    const world = new World();
+    const map = new GameMap(10, 10);
+    const e = createNPC(world, 5, 5, 80, 70);
+    addStats(world, e, { constitution: 10 });
+    const brain = world.getComponent<NPCBrain>(e, 'npcBrain')!;
+    brain.currentGoal = 'sleep';
+    npcBrainSystem(world, map, 0.63, undefined, rc);
+    expect(brain.currentGoal).toBe('sleep');
+  });
+
+  it('uses normal wake logic during nighttime sleep (nap does not apply)', () => {
+    const world = new World();
+    const map = new GameMap(10, 10);
+    const e = createNPC(world, 5, 5, 80, 70);
+    addStats(world, e, { constitution: 10 });
+    const brain = world.getComponent<NPCBrain>(e, 'npcBrain')!;
+    brain.currentGoal = 'sleep';
+    npcBrainSystem(world, map, 0.8, undefined, rc);
+    expect(brain.currentGoal).toBe('sleep');
+  });
+
+  it('high CON NPC has lower nap target (shorter nap)', () => {
+    const world = new World();
+    const map = new GameMap(10, 10);
+    const e = createNPC(world, 5, 5, 80, 75);
+    addStats(world, e, { constitution: 14 });
+    const brain = world.getComponent<NPCBrain>(e, 'npcBrain')!;
+    brain.currentGoal = 'sleep';
+    npcBrainSystem(world, map, 0.4, undefined, rc);
+    expect(brain.currentGoal).not.toBe('sleep');
+  });
+
+  it('low CON NPC has higher nap target (longer nap)', () => {
+    const world = new World();
+    const map = new GameMap(10, 10);
+    const e = createNPC(world, 5, 5, 80, 75);
+    addStats(world, e, { constitution: 6 });
+    const brain = world.getComponent<NPCBrain>(e, 'npcBrain')!;
+    brain.currentGoal = 'sleep';
+    npcBrainSystem(world, map, 0.4, undefined, rc);
+    expect(brain.currentGoal).toBe('sleep');
+  });
+
+  it('clamps nap target to 100 for early morning crashes', () => {
+    const world = new World();
+    const map = new GameMap(10, 10);
+    const e = createNPC(world, 5, 5, 80, 99);
+    addStats(world, e, { constitution: 10 });
+    const brain = world.getComponent<NPCBrain>(e, 'npcBrain')!;
+    brain.currentGoal = 'sleep';
+    npcBrainSystem(world, map, 0.1, undefined, rc);
+    expect(brain.currentGoal).toBe('sleep');
+  });
 });
 
 describe('movementSystem', () => {