[ydflow]

Description

The legacy Python MCP server's chat and agent_chat tools return partial (or empty) answers as successful results when the SSE connection ends before the backend sends a complete event. Raise a request error on EOF before completion so callers can detect an incomplete answer. Existing server error and complete-event handling are preserved.

Type of Change

• 🐛 Bug fix

Testing

• python -m unittest test_chat_sse test_chat_async_preflight (31 tests passed, Python 3.13 / MCP 2.3.0). Regression cases failed on the unmodified code and cover both chat paths, empty streams, partial answers, and unterminated frames.
• git diff --check origin/main...HEAD passed.
• python -m unittest discover -p 'test_*.py' (62 tests): 3 errors in test_file_path_security on Windows (temporary directory cleanup permissions and missing symlink privilege), and test_mcp_transports.HttpStatelessSmokeTest timed out waiting for the HTTP server. The targeted chat tests passed. Full repository checks were not run; this change is limited to the legacy Python MCP server.

Checklist

• git diff --check origin/main...HEAD passes
• Targeted tests for the changed components pass
• Full-repository checks were run, or limitations are documented above
• Self-reviewed the code
• Added/updated tests covering the change