diff --git a/apps/backend/src/__tests__/presence.reconciliation.test.ts b/apps/backend/src/__tests__/presence.reconciliation.test.ts
new file mode 100644
index 0000000..08f7649
--- /dev/null
+++ b/apps/backend/src/__tests__/presence.reconciliation.test.ts
@@ -0,0 +1,165 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { reconcileBoot, cleanupStaleSockets, setOffline } from '../services/presence.js';
+
+// ── DB mock ────────────────────────────────────────────────────────────────
+const { mockFindMany } = vi.hoisted(() => ({
+  mockFindMany: vi.fn(),
+}));
+
+vi.mock('../db/index.js', () => ({
+  db: {
+    query: {
+      conversationMembers: { findMany: mockFindMany },
+    },
+  },
+}));
+
+vi.mock('../db/schema.js', () => ({
+  conversationMembers: {
+    userId: 'userId',
+    conversationId: 'conversationId',
+  },
+}));
+
+vi.mock('drizzle-orm', () => ({
+  eq: vi.fn((col: unknown, val: unknown) => ({ col, val })),
+}));
+
+// ── Redis & Socket mock ────────────────────────────────────────────────────
+
+describe('Presence Reconciliation & Gateway Boot (#...)', () => {
+  let mockRedis: any;
+  let mockIo: any;
+  let mockSocketsJoin: any;
+  let mockFetchSockets: any;
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+
+    mockSocketsJoin = vi.fn();
+    mockFetchSockets = vi.fn().mockResolvedValue([]);
+
+    mockIo = {
+      in: vi.fn((sid: string) => ({
+        socketsJoin: mockSocketsJoin,
+        fetchSockets: () => mockFetchSockets(sid),
+      })),
+    };
+
+    mockRedis = {
+      scan: vi.fn(),
+      keys: vi.fn(),
+      smembers: vi.fn(),
+      srem: vi.fn(),
+      scard: vi.fn(),
+      del: vi.fn(),
+    };
+  });
+
+  describe('reconcileBoot', () => {
+    it('rebuilds room subscriptions from active Redis socket mappings on boot', async () => {
+      // redis.scan returns presence keys
+      mockRedis.scan
+        .mockResolvedValueOnce(['10', ['presence:user-1', 'presence:user-2']])
+        .mockResolvedValueOnce(['0', []]);
+
+      mockRedis.smembers.mockImplementation(async (key: string) => {
+        if (key === 'presence:user-1') return ['socket-1a', 'socket-1b'];
+        if (key === 'presence:user-2') return ['socket-2a'];
+        return [];
+      });
+
+      mockFindMany.mockImplementation(async ({ where }: any) => {
+        if (where.val === 'user-1') {
+          return [{ conversationId: 'room-alpha' }, { conversationId: 'room-beta' }];
+        }
+        if (where.val === 'user-2') {
+          return [{ conversationId: 'room-gamma' }];
+        }
+        return [];
+      });
+
+      await reconcileBoot(mockIo as any, mockRedis as any);
+
+      expect(mockRedis.scan).toHaveBeenCalledTimes(2);
+      expect(mockFindMany).toHaveBeenCalledTimes(2);
+
+      // user-1 sockets joined room-alpha & room-beta
+      expect(mockIo.in).toHaveBeenCalledWith('socket-1a');
+      expect(mockIo.in).toHaveBeenCalledWith('socket-1b');
+      expect(mockIo.in).toHaveBeenCalledWith('socket-2a');
+      expect(mockSocketsJoin).toHaveBeenCalledWith('room-alpha');
+      expect(mockSocketsJoin).toHaveBeenCalledWith('room-beta');
+      expect(mockSocketsJoin).toHaveBeenCalledWith('room-gamma');
+    });
+
+    it('falls back to redis.keys if redis.scan throws', async () => {
+      mockRedis.scan.mockRejectedValue(new Error('scan not supported'));
+      mockRedis.keys.mockResolvedValue(['presence:user-3']);
+      mockRedis.smembers.mockResolvedValue(['socket-3a']);
+      mockFindMany.mockResolvedValue([{ conversationId: 'room-delta' }]);
+
+      await reconcileBoot(mockIo as any, mockRedis as any);
+
+      expect(mockRedis.keys).toHaveBeenCalledWith('presence:*');
+      expect(mockSocketsJoin).toHaveBeenCalledWith('room-delta');
+    });
+  });
+
+  describe('cleanupStaleSockets', () => {
+    it('removes stale socket IDs from Redis presence set and deletes empty sets', async () => {
+      mockRedis.smembers.mockResolvedValue(['socket-dead', 'socket-alive']);
+
+      mockFetchSockets.mockImplementation(async (sid: string) => {
+        if (sid === 'socket-alive') return [{ id: 'socket-alive' }]; // still connected
+        return []; // dead socket
+      });
+
+      mockRedis.scard.mockResolvedValue(1);
+
+      await cleanupStaleSockets(mockIo as any, mockRedis as any, 'user-1');
+
+      expect(mockRedis.srem).toHaveBeenCalledWith('presence:user-1', 'socket-dead');
+      expect(mockRedis.srem).not.toHaveBeenCalledWith('presence:user-1', 'socket-alive');
+      expect(mockRedis.del).not.toHaveBeenCalled();
+    });
+
+    it('deletes presence key if all sockets were stale and removed', async () => {
+      mockRedis.smembers.mockResolvedValue(['socket-dead-1']);
+      mockFetchSockets.mockResolvedValue([]); // dead socket
+      mockRedis.scard.mockResolvedValue(0);
+
+      await cleanupStaleSockets(mockIo as any, mockRedis as any, 'user-2');
+
+      expect(mockRedis.srem).toHaveBeenCalledWith('presence:user-2', 'socket-dead-1');
+      expect(mockRedis.del).toHaveBeenCalledWith('presence:user-2');
+    });
+
+    it('ignores activeSocketId if passed', async () => {
+      mockRedis.smembers.mockResolvedValue(['socket-new']);
+
+      await cleanupStaleSockets(mockIo as any, mockRedis as any, 'user-3', 'socket-new');
+
+      expect(mockFetchSockets).not.toHaveBeenCalled();
+      expect(mockRedis.srem).not.toHaveBeenCalled();
+    });
+  });
+
+  describe('setOffline', () => {
+    it('removes socket ID and returns true when no sockets remain', async () => {
+      mockRedis.scard.mockResolvedValue(0);
+      const offline = await setOffline(mockRedis as any, 'user-1', 'socket-1');
+      expect(mockRedis.srem).toHaveBeenCalledWith('presence:user-1', 'socket-1');
+      expect(mockRedis.del).toHaveBeenCalledWith('presence:user-1');
+      expect(offline).toBe(true);
+    });
+
+    it('returns false when surviving connections remain', async () => {
+      mockRedis.scard.mockResolvedValue(1);
+      const offline = await setOffline(mockRedis as any, 'user-1', 'socket-1');
+      expect(mockRedis.srem).toHaveBeenCalledWith('presence:user-1', 'socket-1');
+      expect(mockRedis.del).not.toHaveBeenCalled();
+      expect(offline).toBe(false);
+    });
+  });
+});
diff --git a/apps/backend/src/index.ts b/apps/backend/src/index.ts
index d94893c..bafcac8 100644
--- a/apps/backend/src/index.ts
+++ b/apps/backend/src/index.ts
@@ -12,7 +12,19 @@ import { registerMessagingHandlers } from './socket/messaging.js';
 import { app } from './app.js';
 import { redis as appRedis } from './lib/redis.js';
 import { setSocketServer } from './lib/socket.js';
+
+
+import {
+  setOnline,
+  setOffline,
+  refreshPresence,
+  reconcileBoot,
+  cleanupStaleSockets,
+} from './services/presence.js';
+
+
 import { setOnline, setOffline } from './services/presence.js';
+
 import { startHeartbeatTimer, clearHeartbeatTimer } from './services/heartbeat.js';
 import {
   registerDeviceSocket,
@@ -27,6 +39,10 @@ import {
   clearViolations,
 } from './services/rateLimit.js';
 import { registerForBackpressure, unregisterForBackpressure } from './services/backpressure.js';
+
+
+
+
 import {
   buildRpcFetcher,
   buildTreasuryRpcFetcher,
@@ -45,6 +61,27 @@ const io = new Server(httpServer, {
   cors: { origin: '*' },
 });
 
+let isShuttingDown = false;
+
+const handleShutdown = () => {
+  isShuttingDown = true;
+};
+
+process.on('SIGTERM', handleShutdown);
+process.on('SIGINT', handleShutdown);
+
+const origIoClose = io.close.bind(io);
+io.close = ((fn?: () => void) => {
+  isShuttingDown = true;
+  return origIoClose(fn);
+}) as typeof io.close;
+
+const origHttpClose = httpServer.close.bind(httpServer);
+httpServer.close = ((fn?: (err?: Error) => void) => {
+  isShuttingDown = true;
+  return origHttpClose(fn);
+}) as typeof httpServer.close;
+
 setSocketServer(io);
 
 // Record a presence change on the resume streams of everyone who shares a
@@ -146,8 +183,14 @@ io.on('connection', async (socket: AuthSocket) => {
   const presenceVisible = user?.presenceVisible ?? true;
 
   if (appRedis) {
+
+    await cleanupStaleSockets(io, appRedis, userId, socket.id);
+    await setOnline(appRedis, userId, socket.id);
+    if (presenceVisible) {
+
     const becameOnline = await setOnline(appRedis, userId, deviceId);
     if (becameOnline && presenceVisible) {
+
       for (const m of memberships) {
         io.to(m.conversationId).emit('user_online', { userId });
         io.to(m.conversationId).emit('presence_update', { userId, online: true });
@@ -160,20 +203,53 @@ io.on('connection', async (socket: AuthSocket) => {
     }
   }
 
+
+  socket.on('heartbeat', async () => {
+    if (appRedis) {
+      await cleanupStaleSockets(io, appRedis, userId, socket.id);
+      await refreshPresence(appRedis, userId);
+    }
+  });
+
+
   registerMessagingHandlers(io, socket);
 
   // Monitor send-buffer to detect slow/stalled consumers.
   registerForBackpressure(socket);
 
+
+  socket.on('disconnect', async (reason: string) => {
+    console.log('User disconnected:', userId, reason);
+
   socket.on('disconnect', async () => {
     console.log('User disconnected:', userId);
+
     clearHeartbeatTimer(socket.id);
     unregisterDeviceSocket(socket.id);
     unregisterForBackpressure(socket);
     clearViolations(socket.id);
 
+
+    // During a gateway restart we must NOT wipe presence — surviving
+    // devices re-assert via heartbeat and Redis TTLs. This satisfies
+    // #221: Gateway restart does not drop still-connected users to offline.
+    if (
+      isShuttingDown ||
+      reason === 'server shutting down' ||
+      reason === 'server namespace disconnect'
+    ) {
+      return;
+    }
+
+
+
     if (appRedis) {
+
+      await cleanupStaleSockets(io, appRedis, userId, socket.id);
+      const fullyOffline = await setOffline(appRedis, userId, socket.id);
+
       const fullyOffline = await setOffline(appRedis, userId, deviceId);
+
       if (fullyOffline) {
         const user = await db.query.users.findFirst({
           where: eq(users.id, userId),
@@ -230,6 +306,15 @@ async function attachRedisAdapter(): Promise<void> {
     const message = err instanceof Error ? err.message : String(err);
     console.warn(`[socket.io] Redis unavailable (${message}) — running in single-instance mode`);
     await Promise.allSettled([pubClient.quit(), subClient.quit()]);
+  } finally {
+    if (appRedis) {
+      try {
+        await reconcileBoot(io, appRedis);
+        console.log('[presence] Boot reconciliation complete');
+      } catch (err) {
+        console.warn('[presence] Boot reconciliation failed:', err);
+      }
+    }
   }
 }
 
@@ -275,3 +360,5 @@ if (stellarRpcUrl && tokenTransferContractId) {
     '[stellar-listener] STELLAR_RPC_URL or TOKEN_TRANSFER_CONTRACT_ID unset; listener disabled.',
   );
 }
+
+export { httpServer, io };
diff --git a/apps/backend/src/routes/treasury.ts b/apps/backend/src/routes/treasury.ts
index f11d342..f2f9e33 100644
--- a/apps/backend/src/routes/treasury.ts
+++ b/apps/backend/src/routes/treasury.ts
@@ -1,4 +1,8 @@
 import { Router, type IRouter } from 'express';
+
+
+
+
 import { z } from 'zod';
 import { requireAuth, type AuthRequest } from '../middleware/auth.js';
 import { validate } from '../middleware/validate.js';
diff --git a/apps/backend/src/services/presence.ts b/apps/backend/src/services/presence.ts
index 603b70d..20a7f0b 100644
--- a/apps/backend/src/services/presence.ts
+++ b/apps/backend/src/services/presence.ts
@@ -10,7 +10,11 @@
  * - On disconnect/timeout: remove that device entry; if none remain → user offline
  * - GET /users/:id/presence → { online: boolean }
  */
+import type { Server } from 'socket.io';
 import type { Redis } from 'ioredis';
+import { eq } from 'drizzle-orm';
+import { db } from '../db/index.js';
+import { conversationMembers } from '../db/schema.js';
 
 const PRESENCE_TTL = 90; // seconds
 
@@ -110,3 +114,78 @@ export async function isOnline(redis: Redis, userId: string): Promise<boolean> {
   const count = await redis.hlen(key);
   return count > 0;
 }
+
+/**
+ * Remove any socket IDs in the user's presence set that are no longer
+ * connected anywhere in the Socket.IO cluster.
+ */
+export async function cleanupStaleSockets(
+  io: Server,
+  redis: Redis,
+  userId: string,
+  ignoredSocketId?: string,
+): Promise<void> {
+  const key = presenceKey(userId);
+  const socketIds = await redis.smembers(key);
+  if (socketIds.length === 0) return;
+
+  await Promise.all(
+    socketIds.map(async (sid) => {
+      if (ignoredSocketId && sid === ignoredSocketId) return;
+      try {
+        const sockets = await io.in(sid).fetchSockets();
+        if (sockets.length === 0) {
+          await redis.srem(key, sid);
+        }
+      } catch (err) {
+        console.warn(`[presence] Failed to check socket status for ${sid}:`, err);
+      }
+    }),
+  );
+
+  const remaining = await redis.scard(key);
+  if (remaining === 0) {
+    await redis.del(key);
+  }
+}
+
+/**
+ * Rebuild room subscriptions from active Redis socket mappings on gateway boot.
+ */
+export async function reconcileBoot(io: Server, redis: Redis): Promise<void> {
+  let presenceKeys: string[];
+  try {
+    let cursor = '0';
+    presenceKeys = [];
+    do {
+      const [nextCursor, keys] = await redis.scan(cursor, 'MATCH', 'presence:*', 'COUNT', 100);
+      cursor = nextCursor;
+      presenceKeys.push(...keys);
+    } while (cursor !== '0');
+  } catch {
+    presenceKeys = await redis.keys('presence:*');
+  }
+
+  for (const key of presenceKeys) {
+    const userId = key.slice('presence:'.length);
+    if (!userId) continue;
+
+    const socketIds = await redis.smembers(key);
+    if (socketIds.length === 0) continue;
+
+    try {
+      const memberships = await db.query.conversationMembers.findMany({
+        where: eq(conversationMembers.userId, userId),
+        columns: { conversationId: true },
+      });
+
+      for (const socketId of socketIds) {
+        for (const m of memberships) {
+          io.in(socketId).socketsJoin(m.conversationId);
+        }
+      }
+    } catch (err) {
+      console.warn(`[presence] Failed to rebuild subscriptions for ${userId}:`, err);
+    }
+  }
+}