Bug Description

When using the `MEDIA:` directive to send a file attachment to a Discord channel, the file appears to be delivered multiple times (duplicate sends).

Steps to Reproduce

1. Have a text/markdown file ready (e.g., `.md` file)
2. In a Discord channel, instruct the agent to send the file using the MEDIA directive
3. Observe that the file is sent more than once / duplicates appear in the channel

Expected Behavior

The file should be sent exactly once per MEDIA directive invocation.

Environment

• Channel: Discord
• Server: Guild #🔬-研究台

Additional Context

Possibly related to Discord channel attachment handling or MEDIA directive processing logic.