The whole spec-driven development movement has always been a bit odd to me, because it feels more like a traditional grounded approach towards regular software engineering.

I can share my personal approach which has worked fairly well at least on modest legacy repositories (250k lines of code). It's a pretty simple 8-step process:

Design

• Think about broad project objectives (ABOUT.md)

• Deep research around tooling (STACK.md)

• Initial spec and iterate with LLM (SPEC.md)

• Develop broad suite of tests (TDD.md)

• Full expansion into multi-phase plan with adversarial reviews (PLAN.md)

Execution

• Agentic harness (OpenCode) implementation at a per-phase level

• Green light from TDD and further adversarial reviews. Manual sanity checking also occurs at this stage.

• Repeat implementation, test, validation cycle until feature complete

https://mordenstar.com/other/spec-dev