test(mcp-kernel-server): add stdio JSON-RPC E2E transport tests

[Ca23187]

Description

Add end-to-end tests for MCP Kernel Server stdio mode.

These tests start the server with --stdio in a real subprocess and validate
JSON-RPC 2.0 request/response cycles over stdin/stdout. Coverage includes:

• initialize → tools/list → tools/call roundtrip
• unknown JSON-RPC method (-32601)
• unknown MCP tool (MCP-level isError)
• malformed JSON (-32603)

This ensures transport-level protocol compliance beyond handler-level tests.

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to change)
• 📚 Documentation update
• 🧪 Test update
• 🔧 Refactor (no functional changes)

Related Issues

Fixes #286

Checklist

• I have read the CONTRIBUTING.md guidelines
• My code follows the project's code style
• I have added tests that prove my fix/feature works
• All new and existing tests pass (pytest tests/ -v)
• I have updated documentation if needed
• My changes generate no new warnings

Testing

All tests pass on Linux (Ubuntu).
Stdio transport tests are skipped on Windows due to asyncio pipe limitations.

# Commands used to test
pytest modules/mcp-kernel-server/tests/test_stdio_e2e.py

Screenshots (if applicable)

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[imran-siddique]

Excellent work @Ca23187! This is exactly the kind of transport-level testing we needed. The stdio E2E tests complement the existing handler-level tests perfectly.

Code review notes:

• Clean \StdioServer\ abstraction with proper process lifecycle management
• Good use of \selectors\ for non-blocking reads with timeout
• Thorough coverage: initialize → tools/list → tools/call roundtrip, unknown method (-32601), unknown tool (MCP isError), malformed JSON (-32603)
• Correct decision to skip on Windows due to asyncio pipe limitations

Merging — thanks for the contribution! 🎉

[imran-siddique]

ℹ️ This project has moved to microsoft/agent-governance-toolkit. All future development, issues, and PRs should be directed there.