feat(gateway): CommandRegistryService + CommandExecutorService (P8-010) (#178)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

apps/gateway/src/chat/chat.gateway.ts

@@ -12,9 +12,11 @@ import {
 import { Server, Socket } from 'socket.io';
 import type { AgentSessionEvent } from '@mariozechner/pi-coding-agent';
 import type { Auth } from '@mosaic/auth';
-import type { SetThinkingPayload } from '@mosaic/types';
+import type { SetThinkingPayload, SlashCommandPayload } from '@mosaic/types';
 import { AgentService } from '../agent/agent.service.js';
 import { AUTH } from '../auth/auth.tokens.js';
+import { CommandRegistryService } from '../commands/command-registry.service.js';
+import { CommandExecutorService } from '../commands/command-executor.service.js';
 import { v4 as uuid } from 'uuid';
 import { ChatSocketMessageDto } from './chat.dto.js';
 import { validateSocketSession } from './chat.gateway-auth.js';
@@ -38,6 +40,8 @@ export class ChatGateway implements OnGatewayInit, OnGatewayConnection, OnGatewa
   constructor(
     @Inject(AgentService) private readonly agentService: AgentService,
     @Inject(AUTH) private readonly auth: Auth,
+    @Inject(CommandRegistryService) private readonly commandRegistry: CommandRegistryService,
+    @Inject(CommandExecutorService) private readonly commandExecutor: CommandExecutorService,
   ) {}
 
   afterInit(): void {
@@ -55,6 +59,9 @@ export class ChatGateway implements OnGatewayInit, OnGatewayConnection, OnGatewa
     client.data.user = session.user;
     client.data.session = session.session;
     this.logger.log(`Client connected: ${client.id}`);
+
+    // Broadcast command manifest to the newly connected client
+    client.emit('commands:manifest', { manifest: this.commandRegistry.getManifest() });
   }
 
   handleDisconnect(client: Socket): void {
@@ -184,6 +191,16 @@ export class ChatGateway implements OnGatewayInit, OnGatewayConnection, OnGatewa
     });
   }
 
+  @SubscribeMessage('command:execute')
+  async handleCommandExecute(
+    @ConnectedSocket() client: Socket,
+    @MessageBody() payload: SlashCommandPayload,
+  ): Promise<void> {
+    const userId = (client.data.user as { id: string } | undefined)?.id ?? 'unknown';
+    const result = await this.commandExecutor.execute(payload, userId);
+    client.emit('command:result', result);
+  }
+
   private relayEvent(client: Socket, conversationId: string, event: AgentSessionEvent): void {
     if (!client.connected) {
       this.logger.warn(