Add provider-specific usage details, fix streaming usage, and return
usage from all high-level APIs (Chat.Send, Generate[T], Agent.Run).
Breaking changes:
- Chat.Send/SendMessage/SendWithImages now return (string, *Usage, error)
- Generate[T]/GenerateWith[T] now return (T, *Usage, error)
- Agent.Run/RunMessages now return (string, *Usage, error)
New features:
- Usage.Details map for provider-specific token breakdowns
(reasoning, cached, audio, thoughts tokens)
- OpenAI streaming now captures usage via StreamOptions.IncludeUsage
- Google streaming now captures UsageMetadata from final chunk
- UsageTracker.Details() for accumulated detail totals
- ModelPricing and PricingRegistry for cost computation
Closes#2
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Generic functions that use the "hidden tool" technique to force models
to return structured JSON matching a Go struct's schema, replacing the
verbose "tool as structured output" pattern.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
