I don't see how this is 'radically different' given that Claude Code literally has a planning mode.

This is my workflow as well, with the big caveat that 80% of 'work' doesn't require substantive planning, we're making relatively straight forward changes.

Edit: there is nothing fundamentally different about 'annotating offline' in an MD vs in the CLI and iterating until the plan is clear. It's a UI choice.

Spec Driven Coding with AI is very well established, so working from a plan, or spec (they can be somewhat different) is not novel.

This is conventional CC use.