What you're describing as "agentic for non-vibe coders" is essentially what responsible AI-assisted development looks like: maintaining human oversight, having clear architecture docs, keeping context alive across sessions. The vibe coding approach tends to skip all of this, which is why so many projects hit a wall after the initial sprint.
This is exactly the territory the Agile Vibe Coding Manifesto (https://agilevibecoding.org) tries to address. It extends the original Agile Manifesto specifically for environments where AI agents are generating significant code. A few of its principles are directly relevant here: "Context is explicit and versioned" and "Architecture guides and constrains generation" — both of which describe what you're doing with your PITCH.md/ARCHITECTURE/IMPLEMENTATION approach.
Worth a read if you're thinking about how to formalize these practices across a team.