Negotiate Compatible MCP Protocols with MCP Clients

[xbill9]

Describe the bug

This merged PR changed the default MCP protocol:
https://github.com/modelcontextprotocol/modelcontextprotocol/pull/655/files

Gemini CLI does not recognize the 2020 MCP Protocol Version

google-gemini/gemini-cli#14970

A clear and concise description of what the bug is.

To Reproduce

in rmcp 0.8.5 the MCP protocol was sent as draft 7
after this the MCP protocol is sent with the 2020 version

the versions on the official MCP protocol site also do not align to the rmcp
code base- for example:

https://modelcontextprotocol.io/specification/2025-11-25

Expected behavior
A clear and concise description of what you expected to happen.

the protocols should negotiate according to the spec:

https://modelcontextprotocol.io/specification/versioning#negotiation

Logs
If applicable, add logs to help explain your problem.

Additional context
Add any other context about the problem here.