- Download and cache .pdf, .docx, .xlsx, .pptx attachments locally
instead of passing expiring CDN URLs to the agent
- Inject .txt and .md content (≤100 KB) into event.text so the agent
sees file content without needing to fetch the URL
- Add 20 MB size guard and SUPPORTED_DOCUMENT_TYPES allowlist
- Fix: unsupported types (.zip etc.) no longer get MessageType.DOCUMENT
- Add 9 unit tests in test_discord_document_handling.py
Mirrors the Slack implementation from PR #784. Discord CDN URLs are
publicly accessible so no auth header is needed (unlike Slack).
Co-authored-by: Dilee <uzmpsk.dilekakbas@gmail.com>
