Note

Adds extensive tests for VercelProvider mapping/streaming behavior and makes getAIMetricsFromStream robust to rejected usage promises with fallback logic.

• Tests (__tests__/VercelProvider.test.ts):
  • Add coverage for toVercelAISDK:
    • Handles undefined model/messages, merges additional messages, maps parameters, supports provider map, and throws on undetermined model/provider.
  • Add coverage for getAIMetricsFromStream:
    • Extracts usage from totalUsage (preferred) or usage, handles missing/errored finishReason, absent usage, rejected usage/totalUsage, and supports v4/v5 token fields.
• Source (src/VercelProvider.ts):
  • Update getAIMetricsFromStream to catch rejections from totalUsage/usage and fall back gracefully; leave success based on finishReason.

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