Implements a feature or bug fix test-first - write one failing test, watch it fail, write the minimal code to pass, then refactor with tests green. This is the implementation stage inside the delivery-flow workflow, entered by requests like "implement this feature", "fix this bug", "write the code for this", or "add the tests and implement it" once delivery-flow is driving the change. Do not activate directly for a standalone request that has not gone through delivery-flow first.