Migrate MCP server from fastapi_mcp to MCP Python SDK #6252

Problem

fastapi_mcp crashes with RecursionError on any self-referencing Pydantic model in the OpenAPI schema (no cycle detection in resolve_schema_references()). This is app-wide — one recursive route kills the entire MCP server. It also generates LLM-unfriendly schemas ($ref/$defs) and HTTP-derived tool names (post_get_online_features).

Solution

Replace fastapi_mcp with the MCP Python SDK (FastMCP). Define tools explicitly via @mcp.tool(), calling FeatureStore methods directly (no internal HTTP round-trip).

Benefits

• Unblocks recursive Pydantic models (compound filters, nested types) on HTTP routes without breaking MCP
• Flat, LLM-friendly tool schemas (no $ref/$defs)
• Semantic tool names (get_online_features, not post_get_online_features)
• New registry discovery tools (list_feature_views, list_entities, list_feature_services, list_data_sources)
• No HTTP noise (health checks, static files, WebSocket routes not exposed)
• Direct FeatureStore calls instead of internal HTTP round-trip