Overview
Use cross-vendor mode when the decision warrants extra thoroughness and the user wants the perspectives of several model families in one coordinated process.
The decision prompt should remain the same kind of detailed strategic brief used in default mode. The difference is not that the question becomes less specific. The difference is that the council routes the work across several models before review and synthesis.
Inspect the model-level outputs after the run. Compare where they agree, where they differ, and whether the final recommendation reflects the range of responses shown in the council trace.