feat(chat): add chat.thread() for creating thread handles

[bensabic]

• Add chat.thread(threadId) method to create a Thread handle from a thread ID outside of webhook contexts
• Adapter is inferred from the thread ID prefix (e.g. slack:, teams:, gchat:)
• Enables proactive messaging to existing threads (cron jobs, external triggers, etc.)
• This was the missing piece for the "Using the adapter outside webhooks" docs example — getInstallation() and withBotToken() already exist

const install = await slackAdapter.getInstallation(teamId);
if (!install) throw new Error("Workspace not installed");

await slackAdapter.withBotToken(install.botToken, async () => {
  const thread = chat.thread("slack:C12345:1234567890.123456");
  await thread.post("Hello from a cron job!");
});

• 4 new unit tests
• Changeset: minor bump on chat

Closes #148

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Project	Deployment	Actions	Updated (UTC)
chat	Ready	Preview, Comment, Open in v0	Apr 14, 2026 5:08am
chat-sdk-nextjs-chat	Ready	Preview, Comment, Open in v0	Apr 14, 2026 5:08am