Refactor plan (maintainer)

This is a living plan; it should stay short and honest.

Near-term

• converge on a single LLM adapter interface
• ensure CLI and API produce equivalent artifacts for equivalent inputs/config

Medium-term

• emit per-phase trace entries (not only finalize)
• strengthen trace upgrade tooling and validation UX

Guardrails

• preserve docs/spec/* invariants unless you version a breaking change
• preserve failure taxonomy and trace schema discipline