HSDD Config: One Phase Context, One Derivative per Coding Method

Before a phase is implemented, build its generic phase context: one self-contained file with everything a coding session needs about the phase, and nothing else. Then wrap it, word for word, in the derivative for the project's coding method: OpenSpec's config.yaml, or a superpowers spec that superpowers:writing-plans starts from. Set up OpenSpec once; switch the phase context before every phase.

Three problems it solves:

1. Lost discipline. Skills are session-scoped; TDD invoked in one session is forgotten in the next. The derivative carries the discipline across the session boundary: config.yaml for OpenSpec, Global Constraints for superpowers.
2. Wasted tokens. A session needs the phase, the contracts it touches and the decisions that govern it, not the full node spec.
3. One method only. The phase context is method-neutral; only the wrapping belongs to a method. A new method is a new derivative, never a change to the generic context.