mcp>=1.0.0 has no upper bound — resolves to incompatible mcp==2.0.0, ccc mcp crashes with ModuleNotFoundError

[louisje]

Summary

pyproject.toml declares mcp>=1.0.0 with no upper bound. On a fresh uv tool install cocoindex-code[full], the resolver picks the latest available mcp (currently 2.0.0), which no longer ships mcp.server.fastmcp (the module appears to have been restructured/renamed, e.g. into mcp.server.mcpserver). Since cocoindex_code/server.py still does from mcp.server.fastmcp import FastMCP, ccc mcp crashes on startup.

Environment

• cocoindex-code v0.2.39 (latest at time of filing)
• Installed via uv tool install cocoindex-code[full]
• Resulting mcp version: 2.0.0
• Python 3.12.9 (uv-managed)
• Linux

Steps to reproduce

uv tool install cocoindex-code[full]
cd <any project>
ccc init
ccc mcp

Actual result

ModuleNotFoundError: No module named 'mcp.server.fastmcp'

Full traceback (trimmed to the relevant frames):

File ".../cocoindex_code/cli.py", line 1041, in mcp
    asyncio.run(_run_mcp())
File ".../cocoindex_code/cli.py", line 1028, in _run_mcp
    from .server import create_mcp_server, run_heartbeat_loop
File ".../cocoindex_code/server.py", line 17, in <module>
    from mcp.server.fastmcp import FastMCP
ModuleNotFoundError: No module named 'mcp.server.fastmcp'

This also surfaces indirectly when the MCP client (e.g. Claude Code) tries to connect to the ccc mcp server and gets -32000: Connection closed, since the subprocess dies immediately on import.

Root cause

pyproject.toml:

dependencies = [
    "mcp>=1.0.0",
    ...
]

No upper bound means any future mcp major release that changes its public API (as 2.0.0 apparently did, removing/renaming mcp.server.fastmcp) will silently break cocoindex-code for new installs, with no warning at install time.

Workaround

Force-install a compatible mcp version:

uv tool install "cocoindex-code[full]" --with 'mcp<2.0' --force

This resolves mcp==1.29.0 (which still has mcp.server.fastmcp) and ccc mcp starts correctly.

Suggested fix

Pin an upper bound on mcp in pyproject.toml, e.g. mcp>=1.0.0,<2.0.0, until the codebase is updated to support mcp 2.x's new API surface (or add explicit support for both and adjust the constraint accordingly).

Happy to provide more details if useful.

[georgeh0]

Thanks for filing the issue. It's fixed in #242.