Dispatch a code-reviewer subagent with precisely scoped context (git SHAs, task description, requirements) to review a diff and return Critical, Important, and Minor findings. Use after delivery-flow finishes implementing and verifying a task, before merging to main. This is the internal code-review stage of the delivery-flow workflow. It is not a standalone entry point, so do not activate it directly for a one-off "review this PR" or "review my code" request; use delivery-flow for those instead.