I'd love to hear more specific details of how this works for you. I am the UX designer for a large web site with user generated content, with an extensive back-end enterprise level CMS. The stuff I work on now is enhancements and improvements to existing features. There is a remote team of back-end and two front-end engineers.

You talk about a prototype being the deliverable from day one. In your process, do you actually have the engineers start building a testable prototype in a QA environment, incrementally testing it and refining the design? I can do clickable prototypes in Figma, but I'm not in the position to create prototypes in a test install of the entire website and CMS. There is always a "hand-off" from Figma to engineering.

How do you manage their time doing both dev work on fully tested designs AND designs in process? Or am I misunderstanding you?

Any additional insight would be appreciated, as I do find that Agile is not terribly UX oriented.