Introduces an opt-in RequestOption that callers can pass to enable
automatic prompt-caching markers. The option populates a cacheConfig
on requestConfig but has no effect yet — plumbing through to
provider.Request and on to the Anthropic provider lands in subsequent
commits.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Cover all core library logic (Client, Model, Chat, middleware, streaming,
message conversion, request building) using a configurable mock provider
that avoids real API calls. ~50 tests across 7 files.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
