[FEATURE] Slack plugin: add slack_pin_message / slack_unpin_message tools

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

The @anthropic/claude-code-slack plugin supports sending messages, adding reactions, and reading channels — but has no tool to pin or unpin messages. Many teams use pinned messages as a review queue (e.g. PR review channels where pinned = "needs review", unpin + reaction = "done"). Without pin/unpin, the agent can post a review request but can't complete the workflow — the user must manually pin in the Slack UI.

Proposed Solution

Add two tools:

1. slack_pin_message — pins a message to a channel

• Parameters: channel_id (string), message_ts (string)
• Maps to Slack's pins.add API

1. slack_unpin_message — unpins a message from a channel

• Parameters: channel_id (string), message_ts (string)
• Maps to Slack's pins.remove API

Both are simple thin wrappers over existing Slack Web API methods. The required OAuth scope is pins:write (likely already granted since chat:write and reactions:write are present).

Alternative Solutions

User manually pins/unpins in the Slack UI after the agent posts.

Priority

Medium - Would be very helpful

Feature Category

Plugins / MCP Tools