feat: Slack Integration

[research-developer]

Overview

Add Slack integration for notifications and slash commands.

Webhook Support ✅

Slack provides multiple webhook mechanisms:

Events API

• app_mention - Bot mentioned in channel
• message - New message in channel
• reaction_added - Emoji reaction added

Slash Commands

Custom commands like /pr-agent review <url>

Identification

• Header: X-Slack-Signature (HMAC SHA256)
• Header: X-Slack-Request-Timestamp
• Payload: Contains team_id, api_app_id
• Challenge: URL verification returns challenge field

Signature Verification

sig_basestring = f"v0:{timestamp}:{body}"
expected = "v0=" + hmac.new(secret, sig_basestring, sha256).hexdigest()

Event Payload

{
  "type": "event_callback",
  "team_id": "T123",
  "api_app_id": "A123",
  "event": {
    "type": "app_mention",
    "user": "U123",
    "text": "<@bot> /review https://github.com/...",
    "channel": "C123"
  }
}

Slash Command Payload

{
  "command": "/pr-agent",
  "text": "review https://github.com/...",
  "response_url": "https://hooks.slack.com/...",
  "trigger_id": "xxx",
  "user_id": "U123",
  "channel_id": "C123"
}

Tasks

• Add Slack Events API webhook handler
• Implement slash commands (/pr-agent review, /pr-agent describe)
• Send PR notifications to Slack channels
• Interactive buttons for PR actions
• Thread replies for PR updates

Use Cases

1. Notifications: Alert channel when PR needs review
2. Commands: /pr-agent review from Slack
3. Summaries: Daily PR summary in channel
4. Approvals: Approve PRs via Slack buttons