feat(config): persist config.patch updates atomically

src/daemon/index.ts

@@ -54,7 +54,11 @@ export interface DaemonContext {
   browserManager?: BrowserManager;
 }
 
-export async function startDaemon(config: Config): Promise<DaemonContext> {
+export interface StartDaemonOptions {
+  configPath?: string;
+}
+
+export async function startDaemon(config: Config, options?: StartDaemonOptions): Promise<DaemonContext> {
   // ── Log level ──
   setLogLevel(config.log_level);
 
@@ -144,7 +148,7 @@ export async function startDaemon(config: Config): Promise<DaemonContext> {
   let channelAgents: ReturnType<typeof createMessageRouter>['agents'] | null = null;
 
   const gateway = createGateway({
-    config, sessionManager, modelRouter, systemPrompt, toolRegistry, toolExecutor,
+    config, configPath: options?.configPath, sessionManager, modelRouter, systemPrompt, toolRegistry, toolExecutor,
     channelRegistry, pairingManager, lifecycle, memoryStore,
     getChannelAgents: () => channelAgents, commandRegistry, intentRegistry, routingPolicy,
   });

src/daemon/services.ts

@@ -1,4 +1,5 @@
 import type { Config } from '../config/index.js';
+import { persistConfig } from '../config/index.js';
 import type { Lifecycle } from './lifecycle.js';
 import type { ToolRegistry, ToolExecutor } from '../tools/index.js';
 import type { AgentOrchestrator } from '../backends/index.js';
@@ -279,6 +280,7 @@ export function initPairingManager(config: Config, store?: PairingStore): Pairin
 
 export interface GatewayDeps {
   config: Config;
+  configPath?: string;
   sessionManager: SessionManager;
   modelRouter: ModelRouter;
   systemPrompt: string;
@@ -295,7 +297,7 @@ export interface GatewayDeps {
 }
 
 export function createGateway(deps: GatewayDeps): GatewayServer {
-  const { config, sessionManager, modelRouter, systemPrompt, toolRegistry, toolExecutor, channelRegistry, pairingManager, lifecycle, getChannelAgents } = deps;
+  const { config, configPath, sessionManager, modelRouter, systemPrompt, toolRegistry, toolExecutor, channelRegistry, pairingManager, lifecycle, getChannelAgents } = deps;
 
   const gateway = new GatewayServer({
     port: config.server.port,
@@ -324,6 +326,11 @@ export function createGateway(deps: GatewayDeps): GatewayServer {
     routingPolicy: deps.routingPolicy,
     uiDir: resolve(import.meta.dirname, '../gateway/ui'),
     config,
+    persistConfig: configPath
+      ? async (nextConfig) => {
+        persistConfig(configPath, nextConfig);
+      }
+      : undefined,
     channelRegistry,
     pairingManager,
     memoryStore: deps.memoryStore,