Function withUsageCollector

Meters a model's token use at construction, for LLM calls whose return shape we don't own: a legacy helper that hands back only its domain result cannot report what it spent, but the model it was handed can. Reads the same usage_metadata as sumMessageUsage, so a metered call counts identically to an agent loop.

const { model, usage } = withUsageCollector(createChartReviewChatModel(SETTINGS));
await someHelperThatOnlyReturnsDocuments({ model });
recordUsage(usage());
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