Builds a single run_code tool backed by provider. One sandbox is created
lazily per runId and reused for that run's later calls, so state (files,
variables) persists across calls within a run. Sandboxes are closed by
closeRun/closeAll or, as a backstop, after idleTtlMs.
Builds a single
run_codetool backed byprovider. One sandbox is created lazily perrunIdand reused for that run's later calls, so state (files, variables) persists across calls within a run. Sandboxes are closed bycloseRun/closeAllor, as a backstop, afteridleTtlMs.