feat(types): add BlockChunk type to chat.{start,append,stop}Stream methods

[srtaalej]

Summary

This PR adds BlocksChunk model class to support the new blocks chunk type in the streaming API (chat.startStream, chat.appendStream, chat.stopStream). Follows the April 16, 2026 changelog which notes updates to the text-streaming API methods to support streaming blocks.

Testing

Sample app.js

import { App, LogLevel } from '@slack/bolt';
import { config } from 'dotenv';

config();

const app = new App({
  token: process.env.SLACK_BOT_TOKEN,
  socketMode: true,
  appToken: process.env.SLACK_APP_TOKEN,
  logLevel: LogLevel.DEBUG,
});

app.message(/^test blocks chunk$/, async ({ message, client, logger }) => {
  try {
    const streamer = client.chatStream({
      channel: message.channel,
      thread_ts: message.ts,
      recipient_team_id: message.team,
      recipient_user_id: message.user,
    });

    await streamer.append({
      markdown_text: "Here's a **card** streamed via `BlocksChunk`:\n\n",
    });

    await streamer.append({
      chunks: [
        {
          type: 'blocks',
          blocks: [
            {
              type: 'card',
              title: { type: 'mrkdwn', text: 'Streaming Card' },
              subtitle: { type: 'mrkdwn', text: 'Sent via BlocksChunk' },
              body: { type: 'mrkdwn', text: 'This card was streamed inside a chunks array.' },
            },
          ],
        },
      ],
    });

    await streamer.stop({
      chunks: [
        {
          type: 'blocks',
          blocks: [
            {
              type: 'carousel',
              elements: [
                {
                  type: 'card',
                  title: { type: 'mrkdwn', text: 'Card 1' },
                  subtitle: { type: 'mrkdwn', text: 'First' },
                  body: { type: 'mrkdwn', text: 'First card in carousel.' },
                },
                {
                  type: 'card',
                  title: { type: 'mrkdwn', text: 'Card 2' },
                  subtitle: { type: 'mrkdwn', text: 'Second' },
                  body: { type: 'mrkdwn', text: 'Second card in carousel.' },
                },
                {
                  type: 'card',
                  title: { type: 'mrkdwn', text: 'Card 3' },
                  subtitle: { type: 'mrkdwn', text: 'Third' },
                  body: { type: 'mrkdwn', text: 'Third card in carousel.' },
                },
              ],
            },
          ],
        },
      ],
    });
  } catch (error) {
    logger.error(error);
  }
});

(async () => {
  try {
    await app.start();
    app.logger.info('⚡️ Bolt app is running!');
  } catch (error) {
    app.logger.error('Failed to start the app', error);
  }
})();

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[changeset-bot]

🦋 Changeset detected

Latest commit: 4589e89

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@slack/types	Patch

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.50%. Comparing base (21b0839) to head (4589e89).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2580   +/-   ##
=======================================
  Coverage   87.50%   87.50%           
=======================================
  Files          62       62           
  Lines       10256    10256           
  Branches      418      418           
=======================================
  Hits         8974     8974           
  Misses       1260     1260           
  Partials       22       22           

Flag	Coverage Δ
cli-hooks	87.50% <ø> (ø)
cli-test	87.50% <ø> (ø)
logger	87.50% <ø> (ø)
oauth	87.50% <ø> (ø)
socket-mode	87.50% <ø> (ø)
web-api	87.50% <ø> (ø)
webhook	87.50% <ø> (ø)

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[zimeg]

@srtaalej Exciting times ahead for streaming chats! I'm marking this with a few changes requested before this merge:

⚠️ issue: The sample code doesn't have these block chunks shown in autocomplete. This doesn't error because arguments are passed through but it might not appear as an expected argument for developers.

📚 todo: This is worth a note in the changesets too! I'm thinking we should document this as a web-api change while still releasing the types changes alongside this 🚀

[zimeg]

🧮 quibble: Also if possible can we order new entries in alphabetics?

[zimeg]

@srtaalej Forgive the unexpected editor configurations! I'm finding this appears in a new shell! 📠

This LGTM with the above note and I'm wondering if we want to discuss version schemes for these changes? 🔮

Using a patch version to signal changing fields has been practiced before while a minor might be used for new blocks altogether? Both do seem alright and I'm also curious about releasing this with web-api also since this is surfaced here? 📚

I'm not so confident about calling this a @slack/web-api change but it's something we can add tests for here also with a changeset? 🪬