diff --git a/server/src/systems/__tests__/socialSystem.test.ts b/server/src/systems/__tests__/socialSystem.test.ts
new file mode 100644
index 0000000..d41bbec
--- /dev/null
+++ b/server/src/systems/__tests__/socialSystem.test.ts
@@ -0,0 +1,292 @@
+import { describe, it, expect } from 'vitest';
+import { World } from '../../ecs/World.js';
+import { socialSystem } from '../socialSystem.js';
+import type { Position, Needs, Movement, NPCBrain, SocialState, EntityId } from '@dflike/shared';
+import {
+  AWARENESS_RADIUS,
+  HUNGER_THRESHOLD,
+  ENERGY_THRESHOLD,
+  SOCIAL_GLOBAL_COOLDOWN,
+  SOCIAL_PAIR_COOLDOWN,
+  Direction,
+} from '@dflike/shared';
+
+function createNPC(
+  world: World, x: number, y: number,
+  opts?: { hunger?: number; energy?: number; goal?: string; walking?: boolean },
+): EntityId {
+  const e = world.createEntity();
+  world.addComponent<Position>(e, 'position', { x, y });
+  world.addComponent<Needs>(e, 'needs', {
+    hunger: opts?.hunger ?? 80,
+    energy: opts?.energy ?? 80,
+  });
+  world.addComponent<Movement>(e, 'movement', {
+    state: opts?.walking ? 'walking' : 'idle',
+    target: opts?.walking ? { x: x + 5, y } : null,
+    path: opts?.walking ? [{ x: x + 1, y }, { x: x + 2, y }] : [],
+    direction: 0,
+    moveProgress: 0,
+  });
+  world.addComponent<NPCBrain>(e, 'npcBrain', {
+    currentGoal: (opts?.goal as any) ?? 'wander',
+    goalQueue: [],
+  });
+  world.addComponent<SocialState>(e, 'socialState', {
+    phase: 'none',
+    partnerId: null,
+    phaseTimer: 0,
+    outcome: null,
+    globalCooldown: 0,
+    pairCooldowns: new Map(),
+  });
+  return e;
+}
+
+describe('socialSystem', () => {
+  describe('proximity detection', () => {
+    it('initiates interaction when two idle NPCs are within awareness radius', () => {
+      const world = new World();
+      const a = createNPC(world, 5, 5);
+      const b = createNPC(world, 8, 5);
+      socialSystem(world);
+      const sa = world.getComponent<SocialState>(a, 'socialState')!;
+      const sb = world.getComponent<SocialState>(b, 'socialState')!;
+      expect(sa.phase).toBe('facing');
+      expect(sa.partnerId).toBe(b);
+      expect(sb.phase).toBe('facing');
+      expect(sb.partnerId).toBe(a);
+    });
+
+    it('does not initiate when NPCs are outside awareness radius', () => {
+      const world = new World();
+      const a = createNPC(world, 0, 0);
+      const b = createNPC(world, 10, 0);
+      socialSystem(world);
+      const sa = world.getComponent<SocialState>(a, 'socialState')!;
+      const sb = world.getComponent<SocialState>(b, 'socialState')!;
+      expect(sa.phase).toBe('none');
+      expect(sb.phase).toBe('none');
+    });
+
+    it('skips player-controlled entities', () => {
+      const world = new World();
+      const a = createNPC(world, 5, 5);
+      const b = createNPC(world, 8, 5);
+      world.addComponent(b, 'playerControlled', { playerId: 'p1', mode: 'avatar' });
+      socialSystem(world);
+      const sa = world.getComponent<SocialState>(a, 'socialState')!;
+      expect(sa.phase).toBe('none');
+    });
+  });
+
+  describe('target rejection', () => {
+    it('rejects target on eat goal with low hunger', () => {
+      const world = new World();
+      const a = createNPC(world, 5, 5);
+      const b = createNPC(world, 8, 5, { goal: 'eat', hunger: HUNGER_THRESHOLD - 5 });
+      socialSystem(world);
+      const sa = world.getComponent<SocialState>(a, 'socialState')!;
+      const sb = world.getComponent<SocialState>(b, 'socialState')!;
+      expect(sa.phase).toBe('none');
+      expect(sb.phase).toBe('none');
+    });
+
+    it('rejects target on rest goal with low energy', () => {
+      const world = new World();
+      const a = createNPC(world, 5, 5);
+      const b = createNPC(world, 8, 5, { goal: 'rest', energy: ENERGY_THRESHOLD - 5 });
+      socialSystem(world);
+      const sa = world.getComponent<SocialState>(a, 'socialState')!;
+      const sb = world.getComponent<SocialState>(b, 'socialState')!;
+      expect(sa.phase).toBe('none');
+      expect(sb.phase).toBe('none');
+    });
+
+    it('allows target on eat goal when hunger is not critical', () => {
+      const world = new World();
+      const a = createNPC(world, 5, 5);
+      const b = createNPC(world, 8, 5, { goal: 'eat', hunger: HUNGER_THRESHOLD + 5 });
+      socialSystem(world);
+      const sa = world.getComponent<SocialState>(a, 'socialState')!;
+      const sb = world.getComponent<SocialState>(b, 'socialState')!;
+      expect(sa.phase).toBe('facing');
+      expect(sb.phase).toBe('facing');
+    });
+  });
+
+  describe('cooldowns', () => {
+    it('respects global cooldown', () => {
+      const world = new World();
+      const a = createNPC(world, 5, 5);
+      const b = createNPC(world, 8, 5);
+      const sa = world.getComponent<SocialState>(a, 'socialState')!;
+      sa.globalCooldown = 10;
+      socialSystem(world);
+      const saAfter = world.getComponent<SocialState>(a, 'socialState')!;
+      expect(saAfter.phase).toBe('none');
+    });
+
+    it('decrements global cooldown each tick', () => {
+      const world = new World();
+      const a = createNPC(world, 5, 5);
+      const sa = world.getComponent<SocialState>(a, 'socialState')!;
+      sa.globalCooldown = 10;
+      socialSystem(world);
+      const saAfter = world.getComponent<SocialState>(a, 'socialState')!;
+      expect(saAfter.globalCooldown).toBe(9);
+    });
+
+    it('respects pair cooldown', () => {
+      const world = new World();
+      const a = createNPC(world, 5, 5);
+      const b = createNPC(world, 8, 5);
+      const sa = world.getComponent<SocialState>(a, 'socialState')!;
+      sa.pairCooldowns.set(b, 10);
+      socialSystem(world);
+      const saAfter = world.getComponent<SocialState>(a, 'socialState')!;
+      expect(saAfter.phase).toBe('none');
+    });
+
+    it('decrements pair cooldowns and removes expired', () => {
+      const world = new World();
+      const a = createNPC(world, 5, 5);
+      const b = createNPC(world, 8, 5);
+      const c = createNPC(world, 20, 20); // far away, just for a second pair cooldown entry
+      const sa = world.getComponent<SocialState>(a, 'socialState')!;
+      sa.pairCooldowns.set(b, 1);
+      sa.pairCooldowns.set(c, 5);
+      socialSystem(world);
+      const saAfter = world.getComponent<SocialState>(a, 'socialState')!;
+      expect(saAfter.pairCooldowns.has(b)).toBe(false);
+      expect(saAfter.pairCooldowns.get(c)).toBe(4);
+    });
+  });
+
+  describe('phase transitions', () => {
+    it('facing -> pausing when timer expires', () => {
+      const world = new World();
+      const a = createNPC(world, 5, 5);
+      const b = createNPC(world, 8, 5);
+      const sa = world.getComponent<SocialState>(a, 'socialState')!;
+      const sb = world.getComponent<SocialState>(b, 'socialState')!;
+      sa.phase = 'facing';
+      sa.partnerId = b;
+      sa.phaseTimer = 1;
+      sb.phase = 'facing';
+      sb.partnerId = a;
+      sb.phaseTimer = 1;
+      socialSystem(world);
+      const saAfter = world.getComponent<SocialState>(a, 'socialState')!;
+      const sbAfter = world.getComponent<SocialState>(b, 'socialState')!;
+      expect(saAfter.phase).toBe('pausing');
+      expect(sbAfter.phase).toBe('pausing');
+    });
+
+    it('pausing -> emoting rolls outcome', () => {
+      const world = new World();
+      const a = createNPC(world, 5, 5);
+      const b = createNPC(world, 8, 5);
+      const sa = world.getComponent<SocialState>(a, 'socialState')!;
+      const sb = world.getComponent<SocialState>(b, 'socialState')!;
+      sa.phase = 'pausing';
+      sa.partnerId = b;
+      sa.phaseTimer = 1;
+      sb.phase = 'pausing';
+      sb.partnerId = a;
+      sb.phaseTimer = 1;
+      socialSystem(world);
+      const saAfter = world.getComponent<SocialState>(a, 'socialState')!;
+      const sbAfter = world.getComponent<SocialState>(b, 'socialState')!;
+      expect(saAfter.phase).toBe('emoting');
+      expect(['positive', 'negative']).toContain(saAfter.outcome);
+      expect(sbAfter.outcome).toBe(saAfter.outcome);
+    });
+
+    it('emoting -> none sets cooldowns', () => {
+      const world = new World();
+      const a = createNPC(world, 5, 5);
+      const b = createNPC(world, 8, 5);
+      const sa = world.getComponent<SocialState>(a, 'socialState')!;
+      const sb = world.getComponent<SocialState>(b, 'socialState')!;
+      sa.phase = 'emoting';
+      sa.partnerId = b;
+      sa.phaseTimer = 1;
+      sb.phase = 'emoting';
+      sb.partnerId = a;
+      sb.phaseTimer = 1;
+      socialSystem(world);
+      const saAfter = world.getComponent<SocialState>(a, 'socialState')!;
+      const sbAfter = world.getComponent<SocialState>(b, 'socialState')!;
+      expect(saAfter.phase).toBe('none');
+      expect(saAfter.globalCooldown).toBe(SOCIAL_GLOBAL_COOLDOWN);
+      expect(saAfter.pairCooldowns.get(b)).toBe(SOCIAL_PAIR_COOLDOWN);
+      expect(sbAfter.phase).toBe('none');
+      expect(sbAfter.globalCooldown).toBe(SOCIAL_GLOBAL_COOLDOWN);
+      expect(sbAfter.pairCooldowns.get(a)).toBe(SOCIAL_PAIR_COOLDOWN);
+    });
+  });
+
+  describe('direction facing', () => {
+    it('NPCs face each other', () => {
+      const world = new World();
+      const a = createNPC(world, 5, 5);
+      const b = createNPC(world, 8, 5);
+      socialSystem(world);
+      const ma = world.getComponent<Movement>(a, 'movement')!;
+      const mb = world.getComponent<Movement>(b, 'movement')!;
+      expect(ma.direction).toBe(Direction.RIGHT); // 3
+      expect(mb.direction).toBe(Direction.LEFT);  // 1
+    });
+  });
+
+  describe('conflict resolution', () => {
+    it('first initiator claims target; second NPC cannot claim same target', () => {
+      const world = new World();
+      const a = createNPC(world, 0, 0);
+      const b = createNPC(world, 3, 0);
+      const c = createNPC(world, 5, 0);
+      socialSystem(world);
+      const sa = world.getComponent<SocialState>(a, 'socialState')!;
+      const sb = world.getComponent<SocialState>(b, 'socialState')!;
+      const sc = world.getComponent<SocialState>(c, 'socialState')!;
+      // b is within range of both a and c; only one pair should form
+      const bInteracting = sb.phase === 'facing';
+      if (bInteracting) {
+        // b is paired with exactly one of a or c
+        const bPartner = sb.partnerId;
+        expect([a, c]).toContain(bPartner);
+        // the other NPC should remain in 'none'
+        const other = bPartner === a ? c : a;
+        const sOther = world.getComponent<SocialState>(other, 'socialState')!;
+        expect(sOther.phase).toBe('none');
+      }
+      // at most one pair formed
+      const interacting = [sa, sb, sc].filter(s => s.phase === 'facing');
+      expect(interacting.length).toBeLessThanOrEqual(2);
+    });
+  });
+
+  describe('partner despawn', () => {
+    it('resets remaining NPC when partner is removed from world', () => {
+      const world = new World();
+      const a = createNPC(world, 5, 5);
+      const b = createNPC(world, 8, 5);
+      // Set up an active interaction
+      const sa = world.getComponent<SocialState>(a, 'socialState')!;
+      const sb = world.getComponent<SocialState>(b, 'socialState')!;
+      sa.phase = 'pausing';
+      sa.partnerId = b;
+      sa.phaseTimer = 5;
+      sb.phase = 'pausing';
+      sb.partnerId = a;
+      sb.phaseTimer = 5;
+      // Remove partner b from the world
+      world.removeEntity(b);
+      socialSystem(world);
+      const saAfter = world.getComponent<SocialState>(a, 'socialState')!;
+      expect(saAfter.phase).toBe('none');
+      expect(saAfter.partnerId).toBeNull();
+    });
+  });
+});