Add support for MCP's Streamable HTTP transport

[BrandonShar]

This adds support for the new Streamable HTTP transport that was just added to MCP in v1.8. I based the implementation off of how FastMCP handled it here.

I set it up to be a non-breaking change (with deprecations) and updated the tests accordingly, but there wasn't an SSE integration test that I noticed. I did test this in my project locally and it worked well. Happy to collaborate on some additional testing!

Resolves #1632

[ankit-kapur]

🙌🏽 Waiting for this to get merged soon

[DouweM]

@BrandonShar Thanks Brandon, this looks great! My only concern is that GitHub shows that uv.lock has "2,039 additions, 2,038 deletions". Can you please revert that and run make install again? I'd expect to just see changes related to the mcp package.

[BrandonShar]

Hey @DouweM thanks for the review! Turns out I needed to upgrade my version of uv (I was on 0.6.*). Looks like that made it want to rebuild the entire lock file. Should be good now!

[DouweM]

@BrandonShar Thanks, the code looks good. Can you please update https://ai.pydantic.dev/mcp/client/#sse-client as well? It currently says "The name "HTTP" is used since this implemented will be adapted in future to use the new Streamable HTTP currently in development.", which should be dropped, and it should be made explicit that we support both the older SSE and newer MCP endpoints.

[GustavoRonconi]

very much looking forward to it! @BrandonShar , you need some help?

[DouweM]

@BrandonShar Note that we have some conflicts from some other changes we just merged

[hyperlint-ai]

PR Change Summary

Added support for the Streamable HTTP transport in MCP, ensuring compatibility with existing functionality while introducing new capabilities.

• Implemented Streamable HTTP transport support in MCPServerHTTP
• Updated documentation to reflect changes in transport type
• Ensured non-breaking changes with deprecations and updated tests accordingly

Modified Files

• docs/mcp/client.md

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[BrandonShar]

@DouweM I tweaked the docs a bit and resolved the conflicts. Just an FYI, a few were just formatting, but the linter seems happy with what I already had.

[DouweM]

HTTP Client

[BrandonShar]

@DouweM changes made. Good call on the docs improvements, I appreciate your attention to detail there!