I'm trying to calculate the cost of doing a streamText.

Based on the docs here, I was under the impression I could use gateway.getGenerationInfo({ id: generationId }) in the onFinish hook. But here I just get:

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"data": {
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        "error": "Usage event not found",
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        "id": "gen_01KT4BW3JSXKZG1CHRJRYQASH8",
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        "message": "No usage event found with ID gen_01KT4BW3JSXKZG1CHRJRYQASH8."
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      }

I can see that result.providerMetadata.gateway contains cost information when I log it:

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{
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  cost: '0.00849',
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  marketCost: '0.00849',
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  surchargeCost: '0',
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  gatewayCost: '0.00849',
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  inferenceCost: '0.00849',
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  inputInferenceCost: '0.00744',
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  outputInferenceCost: '0.00105',
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  generationId: 'gen_01KT4C7A322AA7XN4JV02506VR'
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}

However this is untyped in the typescript SDK, with the type JSONObject ?

So what's the verdict here - do I parse/validate the result.providerMetadata.gateway, or should gateway.getGenerationInfo actually work?