Implements Anthropic's prompt caching API to enable significant cost
reduction (up to 90%) and latency improvements (up to 85%) for
requests with repeated content.
Key features:
- Auto-caching heuristics: large system prompts (>3KB), tool
definitions, and long conversations (>4 messages)
- Full backward compatibility: cache_control fields are optional
- Supports both string and block-array system prompt formats
- Cache control on all content types (text, tool_use, tool_result)
Implementation details:
- Added CacheControl, SystemPrompt, and SystemBlock structures
- Updated NativeContentOut and NativeToolSpec with cache_control
- Strategic cache breakpoint placement (last tool, last message)
- Comprehensive test coverage for serialization and heuristics
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
(cherry picked from commit fff04f4edb5e4cb7e581b1b16035da8cc2e55cef)
455eb3b847