Use sem for entity-level (function/class/method) code questions in any Git repo. Four questions, four verbs - where is it (sem find, sem grep), what does my change touch (sem impact), is it correct (sem check), what should a human review (sem certify). Trigger whenever the user asks where something is defined or called, what a change breaks or which tests to run, whether a change is correct, what changed in a commit or PR, or what to review; also use it proactively before refactors and in code review, where line-level git output is noisy.