send errors to pending requests if server closes

[mroch]

Motivation and Context

Fixes #332

The client blocks indefinitely if the server streams close before responding to a pending request.

How Has This Been Tested?

Added a test. Without this fix, the test fails because the request blocks forever.

Breaking Changes

No

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

[mcp-shadow]

Thank you for addressing this issue - it will improve the reliability of the Python SDK.

One small improvement is needed: after sending errors and closing the streams, we should clear the _response_streams dictionary to prevent keeping references to closed streams.

# Current implementation in the PR:
for id, stream in self._response_streams.items():
    error = ErrorData(code=CONNECTION_CLOSED, message="Connection closed")
    await stream.send(JSONRPCError(jsonrpc="2.0", id=id, error=error))
    await stream.aclose()

# Suggested implementation:
for id, stream in self._response_streams.items():
    error = ErrorData(code=CONNECTION_CLOSED, message="Connection closed")
    await stream.send(JSONRPCError(jsonrpc="2.0", id=id, error=error))
    await stream.aclose()
self._response_streams.clear() 

This matches the existing pattern in the codebase where self._response_streams.pop(request_id, None) is used to remove individual streams after use.

With this small change, the PR should be ready to merge.

[ihrpr]

Thank you!!

Would be great to add

self._response_streams.clear() 

before merging.