Make McpAgent extend Agent + Streaming HTTP protocol features

[deathbyknowledge]

Lib changes:

• McpAgent now extends the base Agent class extend McpAgent from Agent #235
• Refactor to only use Agent and Partykit Server primitives. Depends on Allow routing ctx props to Server partykit#268
• Clients can now GET the MCP endpoint to establish a standalone SSE stream for server initiated messages
• Clients can now DELETE the MCP endpoint to terminate a session Support MCP DELETE requests #416
• Tool notifications are now also handled in the Streamable HTTP transport

Tests:

• New tests to check the updated Streamable HTTP bits
• Added E2E tests that deploy (using alchemy) complete MCP servers and test expected behavior with @modelcontextprotocol/sdk. They include authless and OAuth MCP examples.

Streamable HTTP changes adapted from the TS SDK

Run the E2E from /packages/agents with

npm run test:e2e

[changeset-bot]

🦋 Changeset detected

Latest commit: 4e1794f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
agents	Patch
hono-agents	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[deathbyknowledge]

This seems to be a breaking change. The old McpAgent had a custom onError method that clashes with the base Agent method with the same name once we extend it.

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/cloudflare/agents@415

commit: 4e1794f

[whoiskatrin]

this is some really good stuff! @deathbyknowledge great work

[threepointone]

tentative approval pending nits and notes

[threepointone]

Suggested change

	awaitthis.ctx.storage.put("initialized",true);
	// todo: move to sync api once https://github.com/cloudflare/workerd/pull/4895 lands
	awaitthis.ctx.storage.put("initialized",true);

[kentcdodds]

How confident are we that this is going to be merged? Can I safely prepare teaching material based on this PR?

[deathbyknowledge]

How confident are we that this is going to be merged? Can I safely prepare teaching material based on this PR?

We're waiting to release the AI SDK v5 changes to merge this. Should land this week

[kentcdodds]

That is helpful context. Do you have an idea/recommendation for getting:

1. Authentication information into tool handlers
2. request.url information into tool handlers

I know that the extra arg is a TypeScript MCP SDK-specific thing, but this implementation uses the TypeScript MCP SDK so it seems reasonable to expect to be able to use that. But at this point I don't care all that much, I just would like there to be some recommended way to accomplish this. Everything I've tried I've been told that it's not the right way to do it 🙃

[deathbyknowledge]

That is helpful context. Do you have an idea/recommendation for getting:

The comment I left here #426 (comment) should cover all of those

[kentcdodds]

Just saw your message on my PR: #426 (comment)

Thanks for that!

So I take it from your message that it is fine/encouraged/recommended for me to modify ctx.props?

[deathbyknowledge]

It is fine in the context of McpAgent as it's the only to customize the props as of now, as long as it happens in the handlers mentioned in the comment. We'll be improving the ergonomics regardless, to avoid going through so many hoops and possible footguns. I'll make sure to add some docs to cover this in detail.

[kentcdodds]

Sounds good. Thank you for your help!

[kentcdodds]

Oh, one question to be clear. How does McpAgent plan to support the things the extra argument offers:

[deathbyknowledge]

That still needs to be thought out, it might not be directly though an extra argument but not sure yet

[kentcdodds]

That's fine. Just my 2¢, I think it would be good for the ecosystem if Cloudflare's implementation either supported the full TypeScript SDK (preferred) or built its own. Supporting part of the SDK will lead to confusion for folks I think.

[remorses]

LFG