REPL state persists across code_execution_20260120 calls

SDKs (Python, TypeScript, Go, Java, Ruby, PHP, C#) now support code_execution_20260120, the code execution tool version that adds REPL state persistence and is the minimum version for programmatic tool calling. Set tool's type to code_execution_20260120; no beta header required. Available on Claude Fable 5, Claude Mythos 5, Claude Opus 4.5+, and Claude Sonnet 4.5+.