diff --git a/apps/macos/Sources/Clawdis/GatewayProcessManager.swift b/apps/macos/Sources/Clawdis/GatewayProcessManager.swift
index 6dd64ed29..376c89caf 100644
--- a/apps/macos/Sources/Clawdis/GatewayProcessManager.swift
+++ b/apps/macos/Sources/Clawdis/GatewayProcessManager.swift
@@ -1,6 +1,7 @@
 import Foundation
 import OSLog
 import Subprocess
+import Network
 #if canImport(Darwin)
 import Darwin
 #endif
@@ -153,6 +154,10 @@ final class GatewayProcessManager: ObservableObject {
         self.appendLog("[gateway] starting: \(command.joined(separator: " ")) (cwd: \(cwd))\n")
 
         do {
+            // Acquire the same UDS lock the CLI uses to guarantee a single instance.
+            let lockPath = FileManager.default.temporaryDirectory.appendingPathComponent("clawdis-gateway.lock").path
+            let listener = try self.acquireGatewayLock(path: lockPath)
+
             let result = try await run(
                 .name(command.first ?? "clawdis"),
                 arguments: Arguments(Array(command.dropFirst())),
@@ -168,12 +173,31 @@ final class GatewayProcessManager: ObservableObject {
                 await err
             }
 
+            // Release the lock after the process exits.
+            listener.cancel()
+
             await self.handleTermination(status: result.terminationStatus)
         } catch {
             await self.handleError(error)
         }
     }
 
+    /// Minimal clone of the Node gateway lock: bind a UDS and return the listener.
+    private func acquireGatewayLock(path: String) throws -> NWListener {
+        // Remove stale socket if needed
+        try? FileManager.default.removeItem(atPath: path)
+        let params = NWParameters.tcp
+        params.allowLocalEndpointReuse = false
+        let endpoint = NWEndpoint.unix(path: path)
+        let listener = try NWListener(using: params, on: endpoint)
+        listener.newConnectionHandler = { connection in
+            // Any new connection indicates another starter; reject.
+            connection.cancel()
+        }
+        listener.start(queue: .global())
+        return listener
+    }
+
     private func didStart(_ execution: Execution) {
         self.execution = execution
         self.stopping = false
diff --git a/src/cli/program.ts b/src/cli/program.ts
index 2b2f0d963..301de269b 100644
--- a/src/cli/program.ts
+++ b/src/cli/program.ts
@@ -10,6 +10,7 @@ import { statusCommand } from "../commands/status.js";
 import { callGateway, randomIdempotencyKey } from "../gateway/call.js";
 import { startGatewayServer } from "../gateway/server.js";
 import { danger, info, setVerbose } from "../globals.js";
+import { GatewayLockError } from "../infra/gateway-lock.js";
 import { loginWeb, logoutWeb } from "../provider-web.js";
 import { runRpcLoop } from "../rpc/loop.js";
 import { defaultRuntime } from "../runtime.js";
@@ -325,6 +326,11 @@ Examples:
       try {
         await startGatewayServer(port);
       } catch (err) {
+        if (err instanceof GatewayLockError) {
+          defaultRuntime.error(`Gateway failed to start: ${err.message}`);
+          defaultRuntime.exit(1);
+          return;
+        }
         defaultRuntime.error(`Gateway failed to start: ${String(err)}`);
         defaultRuntime.exit(1);
       }
diff --git a/src/gateway/server.ts b/src/gateway/server.ts
index 96b99b818..bca925000 100644
--- a/src/gateway/server.ts
+++ b/src/gateway/server.ts
@@ -1,6 +1,7 @@
 import { randomUUID } from "node:crypto";
 import os from "node:os";
 import { type WebSocket, WebSocketServer } from "ws";
+import { GatewayLockError, acquireGatewayLock } from "../infra/gateway-lock.js";
 import { createDefaultDeps } from "../cli/deps.js";
 import { agentCommand } from "../commands/agent.js";
 import { getHealthSnapshot } from "../commands/health.js";
@@ -102,6 +103,12 @@ function formatError(err: unknown): string {
 }
 
 export async function startGatewayServer(port = 18789): Promise<GatewayServer> {
+  const releaseLock = await acquireGatewayLock().catch((err) => {
+    // Bubble known lock errors so callers can present a nice message.
+    if (err instanceof GatewayLockError) throw err;
+    throw new GatewayLockError(String(err));
+  });
+
   const wss = new WebSocketServer({
     port,
     host: "127.0.0.1",
@@ -623,6 +630,7 @@ export async function startGatewayServer(port = 18789): Promise<GatewayServer> {
 
   return {
     close: async () => {
+      await releaseLock();
       providerAbort.abort();
       broadcast("shutdown", {
         reason: "gateway stopping",