feat: add channel adapter abstraction with Telegram and WebChat adapters

Implement Phase 3 channel adapters that decouple message sources from
the agent via a uniform ChannelAdapter interface and ChannelRegistry.

- Add ChannelAdapter/InboundMessage/OutboundMessage types
- Add ChannelRegistry for adapter lifecycle and message routing
- Add TelegramAdapter (grammy bot, auth middleware, confirmations, chunking)
- Add WebChatAdapter (thin shim over GatewayServer)
- Refactor daemon to use ChannelRegistry with per-channel-per-user agents
- Add config.get/config.patch gateway handlers (Phase 2 loose end)
- Add system.restart gateway handler (Phase 2 loose end)
- Add implementation plans and design docs

Tests: 225 passing (33 new channel adapter + gateway handler tests)

src/channels/types.ts

@@ -0,0 +1,75 @@
+/**
+ * Channel adapter type definitions.
+ *
+ * Pure type definitions for the channel abstraction layer.
+ * Each channel adapter (Telegram, webchat, etc.) implements
+ * the ChannelAdapter interface to provide a uniform messaging API.
+ */
+
+/** Inbound message received from a channel platform. */
+export interface InboundMessage {
+  /** Platform message ID. */
+  id: string;
+  /** Adapter name: "telegram", "webchat", etc. */
+  channel: string;
+  /** Platform user ID. */
+  senderId: string;
+  /** Display name (optional). */
+  senderName?: string;
+  /** Message text. */
+  text: string;
+  /** ID of message being replied to. */
+  replyTo?: string;
+  /** Unix ms. */
+  timestamp: number;
+  /** Platform-specific extras. */
+  metadata?: Record<string, unknown>;
+}
+
+/** Outbound message to send via a channel adapter. */
+export interface OutboundMessage {
+  /** Response text (markdown). */
+  text: string;
+  /** Original message ID to reply to. */
+  replyTo?: string;
+  /** Platform-specific extras. */
+  metadata?: Record<string, unknown>;
+}
+
+/** Tool execution status event for streaming feedback. */
+export interface ToolStatusEvent {
+  type: 'start' | 'end';
+  tool: string;
+  args?: unknown;
+  result?: { success: boolean; output: string; error?: string };
+}
+
+/** Connection status of a channel adapter. */
+export type ChannelStatus = 'disconnected' | 'connecting' | 'connected' | 'error';
+
+/** Uniform interface that every channel adapter must implement. */
+export interface ChannelAdapter {
+  /** Unique channel name (e.g. "telegram", "webchat"). */
+  readonly name: string;
+
+  /** Current connection status. */
+  readonly status: ChannelStatus;
+
+  /** Start the adapter (connect to platform, begin listening). */
+  connect(): Promise<void>;
+
+  /** Stop the adapter (disconnect, clean up). */
+  disconnect(): Promise<void>;
+
+  /** Send a message to a specific peer on this channel. */
+  send(peerId: string, message: OutboundMessage): Promise<void>;
+
+  /** Register the inbound message handler. Called by registry before connect(). */
+  onMessage(handler: (msg: InboundMessage) => void): void;
+}
+
+/** Callback type for the registry's message handler. */
+export type MessageHandler = (
+  msg: InboundMessage,
+  reply: (response: OutboundMessage) => Promise<void>,
+) => Promise<void>;