Allowing background agents to receive .mdc plans and files to test with

Feature request for product/service

Background Agent (GitHub, Slack, Linear,…)

Describe the request

Would be good to be able to attach files such as .mdc with plans, or to be able to iterate and plan in the UI before the plan, not doing this right can make the agent not do well.
I want to attach a .mdc with a plan and also a file for it to test with but I can’t

Screenshot / Screen Recording