This skill should be used when the user says "arness code plan", "arn-code-plan", "plan this", "write a plan", "create plan", "implementation plan", "plan feature", "plan the spec", "plan from spec", "generate plan", "arness code plan FEATURE_X", "plan the bugfix", "plan bugfix", "make a plan", or wants to generate an implementation plan from a Arness specification. The skill invokes the arn-code-feature-planner agent to generate the plan, presents it for review, and iterates on user feedback until approved. Produces a PLAN_PREVIEW file that feeds into /arn-code-save-plan.