Tool calls were stored in a global map and only cleaned up on tool errors, causing unbounded retention in tool-heavy apps (and potential OOMs when inputs/outputs were recorded). Store only span context in a bounded LRU cache and clean up on successful tool results; add tests for caching/eviction.

Before submitting a pull request, please take a look at our
Contributing guidelines and verify:

• If you've added code that should be tested, please add tests.
• Ensure your code lints and the test suite passes (yarn lint) & (yarn test).
• Link an issue if there is one related to your pull request. If no issue is linked, one will be auto-generated and linked.

Closes #issue_link_here