Create structured implementation plans for autonomous TDD development. Use for new features, multi-file changes, or anything requiring multiple steps or tests. Triggers on aspirational openers ("let's build", "let's start building", "I want to make", "I want an app that", "help me build"), capability lists ("users should be able to X, Y, Z"), vague-noun patterns ("a system for", "a way to", "an app that", "functionality for"), and explicit build verbs ("build", "create", "add a feature", "help me implement", "I need to build"). Do NOT use this for "implement the plan" or "run the plan" - those should use plan-orchestrate instead. Skip for quick bug fixes, single-line changes, questions, or documentation.