fix(ai-amazon-bedrock): emit streaming "finish" after metadata arrives

[tsushanth]

Closes #6237.

Summary

The Bedrock Converse stream sends metadata (with the populated usage block) after messageStop. The SDK was emitting the "finish" part synchronously on messageStop, capturing the still-empty { inputTokens: undefined, outputTokens: undefined, totalTokens: undefined } defaults — so the caller's terminal stream event always saw usage.inputTokens === undefined and usage.outputTokens === undefined, matching the reporter's symptom exactly.

Fix

Buffer the finish reason on messageStop, then emit "finish" from the metadata case once usage, cacheWriteInputTokens, and trace are populated. The output payload shape (reason / usage / metadata.bedrock) is unchanged — only the timing moves.

case "messageStop": {
  finishReason = InternalUtilities.resolveFinishReason(event.messageStop.stopReason)
  break
}

case "metadata": {
  usage.inputTokens = event.metadata.usage.inputTokens
  // ... existing usage / cacheWrite / trace population ...
  if (Predicate.isNotUndefined(finishReason)) {
    parts.push({ type: "finish", reason: finishReason, usage, metadata: { bedrock: { trace, usage: { cacheWriteInputTokens } } } })
    finishReason = undefined
  }
  break
}

Notes

I didn't add a streaming test — converseStream is null as any in the existing test harness in AmazonBedrockLanguageModel.test.ts, so there's no pattern yet for mocking ConverseResponseStreamEvent. Happy to follow up with a focused stream test once the maintainers point at the preferred mocking shape.

[changeset-bot]

🦋 Changeset detected

Latest commit: d6cac31

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@effect/ai-amazon-bedrock	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR