fix(channels): bridge openDM delegates to adapter directly

chat.openDM dispatches via inferAdapterFromUserId, which only recognizes
Discord/Slack/Teams/gChat formats and throws for everything else —
breaking approval delivery on Telegram (numeric IDs) and the other
direct-addressable channels the bridge now wraps. Delegate straight to
adapter.openDM + channelIdFromThreadId, and only expose openDM when the
underlying adapter implements it. Preserves the adapter's native
platform_id encoding (e.g. "telegram:<chatId>") so user_dms caches align
with the messaging_groups rows onInbound wrote.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/channels/chat-sdk-bridge.test.ts

@@ -0,0 +1,38 @@
+import { describe, expect, it } from 'vitest';
+
+import type { Adapter } from 'chat';
+
+import { createChatSdkBridge } from './chat-sdk-bridge.js';
+
+function stubAdapter(partial: Partial<Adapter>): Adapter {
+  return { name: 'stub', ...partial } as unknown as Adapter;
+}
+
+describe('createChatSdkBridge', () => {
+  it('omits openDM when the underlying Chat SDK adapter has none', () => {
+    const bridge = createChatSdkBridge({
+      adapter: stubAdapter({}),
+      supportsThreads: false,
+    });
+    expect(bridge.openDM).toBeUndefined();
+  });
+
+  it('exposes openDM when the underlying adapter has one, and delegates directly', async () => {
+    const openDMCalls: string[] = [];
+    const bridge = createChatSdkBridge({
+      adapter: stubAdapter({
+        openDM: async (userId: string) => {
+          openDMCalls.push(userId);
+          return `thread::${userId}`;
+        },
+        channelIdFromThreadId: (threadId: string) => `stub:${threadId.replace(/^thread::/, '')}`,
+      }),
+      supportsThreads: false,
+    });
+    expect(bridge.openDM).toBeDefined();
+    const platformId = await bridge.openDM!('user-42');
+    // Delegation: adapter.openDM → adapter.channelIdFromThreadId, no chat.openDM in between.
+    expect(openDMCalls).toEqual(['user-42']);
+    expect(platformId).toBe('stub:user-42');
+  });
+});