feat: integrate constitution into needs decay rates

High constitution slows hunger/energy decay, low constitution speeds it.
Uses getEffectiveStat helper which defaults to 10 for entities without
stats, preserving backward compatibility.

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

server/src/systems/__tests__/systems.test.ts

@@ -4,7 +4,7 @@ import { GameMap } from '../../map/GameMap.js';
 import { needsDecaySystem } from '../needsDecaySystem.js';
 import { npcBrainSystem } from '../npcBrainSystem.js';
 import { movementSystem } from '../movementSystem.js';
-import type { Needs, Movement, NPCBrain, Position, SocialState } from '@dflike/shared';
+import type { Needs, Movement, NPCBrain, Position, SocialState, Stats, StatModifiers } from '@dflike/shared';
 import { HUNGER_DECAY_PER_TICK, ENERGY_DECAY_PER_TICK, MOVE_SPEED } from '@dflike/shared';
 
 function createNPC(world: World, x: number, y: number, hunger = 80, energy = 80) {
@@ -16,6 +16,16 @@ function createNPC(world: World, x: number, y: number, hunger = 80, energy = 80)
   return e;
 }
 
+function addStats(world: World, entity: number, overrides: Partial<Stats> = {}): void {
+  const base: Stats = {
+    strength: 10, dexterity: 10, constitution: 10, intelligence: 10, perception: 10,
+    sociability: 10, courage: 10, curiosity: 10, empathy: 10, temperament: 10,
+    ...overrides,
+  };
+  world.addComponent<Stats>(entity, 'stats', base);
+  world.addComponent<StatModifiers>(entity, 'statModifiers', { modifiers: [] });
+}
+
 function addSocialState(world: World, entity: number, phase: SocialState['phase'] = 'none') {
   world.addComponent<SocialState>(entity, 'socialState', {
     phase,
@@ -37,6 +47,34 @@ describe('needsDecaySystem', () => {
     expect(needs.energy).toBeCloseTo(50 - ENERGY_DECAY_PER_TICK);
   });
 
+  it('high constitution slows hunger decay', () => {
+    const world = new World();
+    const e = createNPC(world, 0, 0, 50, 50);
+    addStats(world, e, { constitution: 14 });
+    needsDecaySystem(world);
+    const needs = world.getComponent<Needs>(e, 'needs')!;
+    const expectedDecay = HUNGER_DECAY_PER_TICK * (1 - (14 - 10) * 0.03);
+    expect(needs.hunger).toBeCloseTo(50 - expectedDecay);
+  });
+
+  it('low constitution speeds hunger decay', () => {
+    const world = new World();
+    const e = createNPC(world, 0, 0, 50, 50);
+    addStats(world, e, { constitution: 6 });
+    needsDecaySystem(world);
+    const needs = world.getComponent<Needs>(e, 'needs')!;
+    const expectedDecay = HUNGER_DECAY_PER_TICK * (1 - (6 - 10) * 0.03);
+    expect(needs.hunger).toBeCloseTo(50 - expectedDecay);
+  });
+
+  it('uses default decay when entity has no stats', () => {
+    const world = new World();
+    const e = createNPC(world, 0, 0, 50, 50);
+    needsDecaySystem(world);
+    const needs = world.getComponent<Needs>(e, 'needs')!;
+    expect(needs.hunger).toBeCloseTo(50 - HUNGER_DECAY_PER_TICK);
+  });
+
   it('clamps needs at 0', () => {
     const world = new World();
     const e = createNPC(world, 0, 0, 0.01, 0.01);

server/src/systems/needsDecaySystem.ts

@@ -1,10 +1,13 @@
 import { HUNGER_DECAY_PER_TICK, ENERGY_DECAY_PER_TICK, type Needs } from '@dflike/shared';
 import type { World } from '../ecs/World.js';
+import { getEffectiveStat } from './statHelpers.js';
 
 export function needsDecaySystem(world: World): void {
   for (const entity of world.query('needs')) {
     const needs = world.getComponent<Needs>(entity, 'needs')!;
-    needs.hunger = Math.max(0, needs.hunger - HUNGER_DECAY_PER_TICK);
-    needs.energy = Math.max(0, needs.energy - ENERGY_DECAY_PER_TICK);
+    const con = getEffectiveStat(world, entity, 'constitution');
+    const conMultiplier = 1 - (con - 10) * 0.03;
+    needs.hunger = Math.max(0, needs.hunger - HUNGER_DECAY_PER_TICK * conMultiplier);
+    needs.energy = Math.max(0, needs.energy - ENERGY_DECAY_PER_TICK * conMultiplier);
   }
 }