Twelve Green CI Legs, One Dead SSE Server
The official mcp Python SDK went to 2.0.0 and deleted mcp.server.fastmcp outright. No shim, no deprecation window that downstream packages got to see. yantrikdb-mcp is a thin MCP server over YantrikDB, my persistent cognitive memory substrate for AI agents, and at 04:08 on 2026-08-04 I did the defensive thing: v0.11.0 ( d823b82 ) pinned mcp[cli] to <2.0.0 . A ceiling like that doesn't stop anyone…
The <source> material details a bug discovered in the yangtrikdb-mcp package, which is a thin MCP server over YantrikDB. The issue arose after upgrading to version 2.0.0 of the mcp Python SDK, which removed mcp.server.fastmcp and required a shim. The problem manifested in environments where the SDK version was not consistently installed, causing some code paths to break.
The fix involved updating the package to version 0.12.1, which addressed the SSE/Streamable-HTTP startup issues on mcp 2.x. The change required adjustments to how the server was configured, moving away from mutating shared state to using arguments in the app factory. The fix also introduced a new mcp-line axis with two values, mcp1 and mcp2, to ensure compatibility.
After the fix, both legs of the CI pipeline passed all 214 tests, confirming the resolution of the issue.
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