[BUG] slack_read_channel / slack_read_thread drop message attachments and blocks

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

The slack_read_channel and slack_read_thread tools only return the top-level text field from Slack messages. Content stored in attachments or Block Kit blocks is silently discarded, causing many messages to
appear completely empty even when they have visible content in the Slack UI. Many Slack bots (alerting systems and monitoring tools) store their entire payload in attachments or blocks and set no top-level text field. This makes those messages completely invisible to Claude via the MCP.

What Should Happen?

The tool should surface:

• attachments[].fallback — the plain-text fallback that well-formed attachments always include
• attachments[].text and attachments[].fields[].title / .value
• For Block Kit: plain_text andmrkdwn leaf nodes from the blocks[] tree

Error Messages/Logs

Steps to Reproduce

1. Connect the claude.ai Slack MCP integration
2. Find a channel containing bot messages that use attachments or blocks (common for CI bots, alerting systems, monitoring tools, etc.)
3. Call slack_read_channel — those messages return as empty strings

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.104 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_