In digging through the code I have a nasty suspicion that attachments are not fully asyncio safe - I think sometimes when an async model is executing a prompt it may make a blocking call to attachment.base64_content() which calls attachment.content_bytes() which calls a blocking httpx.get(). Fixing this will be tricky because it will involve fixing a bunch of existing plugins.

Originally posted by @simonw in #1142 (comment)