critical

This caching implementation has a critical correctness issue and a potential race condition.

• Correctness Bug (Not Context-Aware): The list of tools returned by get_tools depends on the readonly_context argument, which influences session headers and tool filtering. This implementation caches the tools from the first call and returns this cached list for all subsequent calls, regardless of their context. This will lead to incorrect behavior if get_tools is called with different contexts.

• Race Condition: If multiple coroutines call get_tools() concurrently while the cache is empty, they may all bypass the cache check and proceed to fetch tools from the server simultaneously. This negates the performance benefit of caching.

Due to the correctness bug, I recommend rethinking this caching strategy. An incorrect cache can be more harmful than no cache.

Recommendation:
A more robust solution would involve a context-aware cache. For example, you could cache the result of the expensive session.list_tools() call (which depends on headers) and then re-apply the context-specific filtering (_is_tool_selected) on every get_tools call.

If you are certain that a McpToolset instance will only ever be used with a single, unchanging context, please add a prominent comment or docstring to clarify this assumption. Even in that case, the race condition should be fixed using asyncio.Lock to ensure tools are fetched only once.