"Your Message is Too Long" on First Entry in Chat

Cursor 50.4, I am getting a “Your message is too long. Please try again with a shorter message and fewer/smaller attached items” error on the first entry in a new chat. I am “@-ing” two files, one is ~1700 lines and the other is ~2500 lines, if that matters.

This is in “auto” agent mode btw. If I manually switch to one of the Claude models it does not do this.