The MCP server instructions string omitted three behaviours added in
earlier PRs, leaving agents without context on them:
- send_file / download_file tools (#1829, #1830)
- [file:]/[image:]/[audio:]/[video:] attachment markers in read_room (#1830)
- unread guard: send_message, send_dm, send_file, send_reply all
reject if the room has unread messages; read_room + mark_read
are required first (#1828)
Closes#1828. Closes#1829. Closes#1830.