v2 phase 4: channel adapter interface, registry, and host wiring

ChannelAdapter interface with setup/deliver/teardown/setTyping lifecycle.
Self-registration pattern via channel-registry. Host wiring in index-v2
bridges inbound messages to routeInbound and outbound delivery to adapters.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/channels/channel-registry.ts

@@ -0,0 +1,72 @@
+/**
+ * v2 Channel adapter registry.
+ *
+ * Channels self-register on import. The host calls initChannelAdapters() at startup
+ * to instantiate and set up all registered adapters.
+ */
+import type { ChannelAdapter, ChannelRegistration, ChannelSetup } from './adapter.js';
+import { log } from '../log.js';
+
+const registry = new Map<string, ChannelRegistration>();
+const activeAdapters = new Map<string, ChannelAdapter>();
+
+/** Register a channel adapter factory. Called by channel modules on import. */
+export function registerChannelAdapter(name: string, registration: ChannelRegistration): void {
+  registry.set(name, registration);
+}
+
+/** Get a live adapter by channel type. */
+export function getChannelAdapter(channelType: string): ChannelAdapter | undefined {
+  return activeAdapters.get(channelType);
+}
+
+/** Get all active adapters. */
+export function getActiveAdapters(): ChannelAdapter[] {
+  return [...activeAdapters.values()];
+}
+
+/** Get all registered channel names. */
+export function getRegisteredChannelNames(): string[] {
+  return [...registry.keys()];
+}
+
+/** Get container config for a channel (used by container-runner for additional mounts/env). */
+export function getChannelContainerConfig(name: string): ChannelRegistration['containerConfig'] {
+  return registry.get(name)?.containerConfig;
+}
+
+/**
+ * Instantiate and set up all registered channel adapters.
+ * Skips adapters that return null (missing credentials).
+ */
+export async function initChannelAdapters(setupFn: (adapter: ChannelAdapter) => ChannelSetup): Promise<void> {
+  for (const [name, registration] of registry) {
+    try {
+      const adapter = registration.factory();
+      if (!adapter) {
+        log.warn('Channel credentials missing, skipping', { channel: name });
+        continue;
+      }
+
+      const setup = setupFn(adapter);
+      await adapter.setup(setup);
+      activeAdapters.set(adapter.channelType, adapter);
+      log.info('Channel adapter started', { channel: name, type: adapter.channelType });
+    } catch (err) {
+      log.error('Failed to start channel adapter', { channel: name, err });
+    }
+  }
+}
+
+/** Tear down all active adapters. */
+export async function teardownChannelAdapters(): Promise<void> {
+  for (const [name, adapter] of activeAdapters) {
+    try {
+      await adapter.teardown();
+      log.info('Channel adapter stopped', { channel: name });
+    } catch (err) {
+      log.error('Failed to stop channel adapter', { channel: name, err });
+    }
+  }
+  activeAdapters.clear();
+}