feat: communication spine — gateway, TUI, Discord

Gateway:
- Agent service wrapping Pi SDK createAgentSession (in-process)
- Chat WebSocket gateway (Socket.IO) streaming agent events
- Chat REST controller for synchronous requests
- NestJS module structure: AgentModule (global), ChatModule

CLI:
- Ink-based TUI client connecting to gateway via WebSocket
- Commander-based CLI with `mosaic tui` command
- Streaming message display with React components

Discord:
- Discord.js bot with mention-based activation + DM support
- Routes messages through gateway WebSocket
- Chunked response delivery (2000-char Discord limit)
- Single-guild binding for v0.1.0

Architecture: All channels → Gateway WebSocket → Pi SDK → LLM

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

plugins/discord/package.json

@@ -11,11 +11,17 @@
   },
   "scripts": {
     "build": "tsc",
+    "dev": "tsx watch src/index.ts",
     "lint": "eslint src",
     "typecheck": "tsc --noEmit",
     "test": "vitest run"
   },
+  "dependencies": {
+    "discord.js": "^14.16.0",
+    "socket.io-client": "^4.8.0"
+  },
   "devDependencies": {
+    "tsx": "^4.0.0",
     "typescript": "^5.8.0",
     "vitest": "^2.0.0"
   }

plugins/discord/src/index.ts

@@ -1 +1,153 @@
-export const VERSION = '0.0.0';
+import { Client, GatewayIntentBits, type Message as DiscordMessage } from 'discord.js';
+import { io, type Socket } from 'socket.io-client';
+
+export interface DiscordPluginConfig {
+  token: string;
+  gatewayUrl: string;
+  /** Which guild to bind to (single-guild only for v0.1.0) */
+  guildId?: string;
+}
+
+export class DiscordPlugin {
+  private client: Client;
+  private socket: Socket | null = null;
+  private config: DiscordPluginConfig;
+  /** Map Discord channel ID → Mosaic conversation ID */
+  private channelConversations = new Map<string, string>();
+  /** Track in-flight responses to avoid duplicate streaming */
+  private pendingResponses = new Map<string, string>();
+
+  constructor(config: DiscordPluginConfig) {
+    this.config = config;
+    this.client = new Client({
+      intents: [
+        GatewayIntentBits.Guilds,
+        GatewayIntentBits.GuildMessages,
+        GatewayIntentBits.MessageContent,
+        GatewayIntentBits.DirectMessages,
+      ],
+    });
+  }
+
+  async start(): Promise<void> {
+    // Connect to gateway WebSocket
+    this.socket = io(`${this.config.gatewayUrl}/chat`, {
+      transports: ['websocket'],
+    });
+
+    this.socket.on('connect', () => {
+      console.log('[discord] Connected to gateway');
+    });
+
+    // Handle streaming text from gateway
+    this.socket.on('agent:text', (data: { conversationId: string; text: string }) => {
+      const pending = this.pendingResponses.get(data.conversationId);
+      if (pending !== undefined) {
+        this.pendingResponses.set(data.conversationId, pending + data.text);
+      }
+    });
+
+    // When agent finishes, send the accumulated response
+    this.socket.on('agent:end', (data: { conversationId: string }) => {
+      const text = this.pendingResponses.get(data.conversationId);
+      if (text) {
+        this.sendToDiscord(data.conversationId, text);
+        this.pendingResponses.delete(data.conversationId);
+      }
+    });
+
+    this.socket.on('agent:start', (data: { conversationId: string }) => {
+      this.pendingResponses.set(data.conversationId, '');
+    });
+
+    // Set up Discord message handler
+    this.client.on('messageCreate', (message) => this.handleDiscordMessage(message));
+
+    this.client.on('ready', () => {
+      console.log(`[discord] Bot logged in as ${this.client.user?.tag}`);
+    });
+
+    await this.client.login(this.config.token);
+  }
+
+  async stop(): Promise<void> {
+    this.socket?.disconnect();
+    await this.client.destroy();
+  }
+
+  private handleDiscordMessage(message: DiscordMessage): void {
+    // Ignore bot messages
+    if (message.author.bot) return;
+
+    // Check guild binding
+    if (this.config.guildId && message.guildId !== this.config.guildId) return;
+
+    // Respond to DMs always, or mentions in channels
+    const isDM = !message.guildId;
+    const isMention = message.mentions.has(this.client.user!);
+
+    if (!isDM && !isMention) return;
+
+    // Strip bot mention from message content
+    const content = message.content
+      .replace(new RegExp(`<@!?${this.client.user!.id}>`, 'g'), '')
+      .trim();
+
+    if (!content) return;
+
+    // Get or create conversation for this Discord channel
+    const channelId = message.channelId;
+    let conversationId = this.channelConversations.get(channelId);
+    if (!conversationId) {
+      conversationId = `discord-${channelId}`;
+      this.channelConversations.set(channelId, conversationId);
+    }
+
+    // Send to gateway
+    this.socket?.emit('message', {
+      conversationId,
+      content,
+    });
+  }
+
+  private sendToDiscord(conversationId: string, text: string): void {
+    // Find the Discord channel for this conversation
+    const channelId = Array.from(this.channelConversations.entries()).find(
+      ([, convId]) => convId === conversationId,
+    )?.[0];
+
+    if (!channelId) return;
+
+    const channel = this.client.channels.cache.get(channelId);
+    if (!channel || !('send' in channel)) return;
+
+    // Chunk responses for Discord's 2000-char limit
+    const chunks = this.chunkText(text, 1900);
+    for (const chunk of chunks) {
+      (channel as { send: (content: string) => Promise<unknown> }).send(chunk);
+    }
+  }
+
+  private chunkText(text: string, maxLength: number): string[] {
+    if (text.length <= maxLength) return [text];
+
+    const chunks: string[] = [];
+    let remaining = text;
+
+    while (remaining.length > 0) {
+      if (remaining.length <= maxLength) {
+        chunks.push(remaining);
+        break;
+      }
+
+      // Try to break at a newline
+      let breakPoint = remaining.lastIndexOf('\n', maxLength);
+      if (breakPoint <= 0) breakPoint = maxLength;
+
+      chunks.push(remaining.slice(0, breakPoint));
+      remaining = remaining.slice(breakPoint).trimStart();
+    }
+
+    return chunks;
+  }
+}