Describe the project
Start a new project and write what you are building in plain language. Attach anything that already exists — a PDF spec, an RFC, a Markdown brief, meeting notes. Foundry reads them and researches the domain in the background.
"Replace our on-prem billing system with a multi-tenant service. 40k merchants, PCI scope, zero-downtime cutover from the PHP monolith."
The more constraints you state up front, the fewer Foundry has to ask about.