How to review code with an agent
Two "Milk" entries in a shopping list, and deleting one wipes out both. The author never hit that case: he added bread and milk. Code review exists for exactly this, and an agent can do it in three requests, where the middle one checks that the finding is real.
A subagent as a separate window of attention
A context window is not infinite: the more files read and command output collected, the sooner Claude Code starts trimming the history. A subagent takes that work into its own window and returns a summary. A plain request runs the first one; a standing role needs a file where reviewer gets only Read, Grep and Glob.
How to brief a subagent for review and check its report
Tell a reviewer to "check the page" and back comes a tidy list of findings about something else. A brief in three parts changes the answer: what to look at, what counts as correct, what to leave alone. An empty report is a result too - demanding five bugs is what produces five bugs.