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Upgrade MCP SDK to v1.25.1 #752

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@mattzcarey mattzcarey commented Dec 24, 2025

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changeset-bot bot commented Dec 24, 2025 •
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⚠️ No Changeset found

Latest commit: aae1db9

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claude bot commented Dec 24, 2025 •
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Claude Code Review

Summary: MCP SDK v1.23.0 → v1.25.1 upgrade with compatibility fixes and new resumability features.

Issues

1. Removed patch file without verification

The patch file patches/@modelcontextprotocol+sdk+1.23.0.patch was deleted. Verify the patch is no longer needed with the new SDK version - review what it fixed and confirm those fixes are either unnecessary or included in v1.25.1.

2. Missing validation in closeSSEStream

packages/agents/src/mcp/worker-transport.ts:773 - The new closeSSEStream method lacks validation:

  • Should check if streamId === standaloneSseStreamId to prevent closing the GET stream
  • No check if transport is started or stream exists before cleanup

3. Error handling edge case

packages/agents/src/mcp/errors.ts:5-15 - getErrorCode doesn't validate code is a safe integer. Could fail with code: NaN or code: Infinity. Consider adding Number.isSafeInteger() check.

4. Example uses deprecated CORS header

examples/mcp-server/src/index.ts:35 - Header mcp-protocol-version should match the SDK constant MCP-Protocol-Version (capitalization matters for case-sensitive headers).

Observations

Positive:

  • Comprehensive test coverage for error utilities (138 lines)
  • Well-documented new options (eventStore, retryInterval, onsessionclosed)
  • Backward-compatible error detection (both code and message)

Note: SDK import changes (isJSONRPCError → isJSONRPCErrorResponse, etc.) are breaking changes from v1.24.0. The fallback error handling correctly addresses the StreamableHTTPError format change.

agents-git-bot bot pushed a commit to cloudflare/cloudflare-docs that referenced this pull request Dec 24, 2025
@github-actions @claude
Sync docs for PR #752: Upgrade MCP SDK to v1.25.1
b09c50e 
This sync updates the documentation to reflect the following changes from
cloudflare/agents PR #752:

## API Changes

### WorkerTransportOptions (mcp-handler-api.mdx)
- Added `onsessionclosed` callback that fires when a session is closed via
  DELETE request
- Added `eventStore` option for SSE resumability support, enabling clients to
  reconnect and resume using Last-Event-ID header
- Added `retryInterval` option to control client reconnection timing for
  polling behavior
- Added `closeSSEStream()` method to WorkerTransport class for implementing
  polling behavior during long-running operations
- Updated `sessionIdGenerator` description to clarify it can return undefined
  for stateless mode

### MCPTransportOptions (mcp-client-api.mdx)
- Added `connectionTimeoutMs` option (default: 15000ms) to prevent infinite
  hangs when connecting to MCP servers. Particularly useful when proxies strip
  SSE newline terminators.

### New Example (transport.mdx)
- Added documentation for the new `mcp-server` example showing how to use
  `WebStandardStreamableHTTPServerTransport` from the MCP SDK directly without
  the agents package. This is the simplest way to create stateless MCP servers
  on Cloudflare Workers.

Related PR: cloudflare/agents#752

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
@agents-git-bot agents-git-bot bot mentioned this pull request Dec 24, 2025
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agents-git-bot bot pushed a commit to cloudflare/cloudflare-docs that referenced this pull request Dec 24, 2025
@github-actions
docs: add stateless MCP server guide and update MCP documentation
4337e31 
This commit documents the new stateless MCP server approach introduced in PR #752 (Upgrade MCP SDK to v1.25.1).

Changes:
- Add new stateless-mcp-server.mdx guide demonstrating WebStandardStreamableHTTPServerTransport usage
- Update MCP index page to explain both stateless and McpAgent-based approaches
- Update remote-mcp-server guide to clarify it uses McpAgent and link to stateless option
- Document the simplest way to create MCP servers on Cloudflare Workers

The new example (examples/mcp-server) uses the MCP SDK directly without the agents package, providing a zero-config stateless option that is simpler for basic use cases.

Related PR: cloudflare/agents#752
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pkg-pr-new bot commented Dec 24, 2025 •
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npm i https://pkg.pr.new/cloudflare/agents@752

commit: aae1db9

agents-git-bot bot pushed a commit to cloudflare/cloudflare-docs that referenced this pull request Dec 24, 2025
@github-actions @claude
docs: Add MCP SDK v1.25.1 documentation
2c52cc6 
Document the MCP SDK upgrade from v1.23.0 to v1.25.1 with the following updates:

- Add new section on using MCP SDK directly without Agents SDK
- Document the new mcp-server example using WebStandardStreamableHTTPServerTransport
- Add documentation for new WorkerTransport options:
  - onsessionclosed callback for session cleanup
  - eventStore for connection resumability support
  - retryInterval for SSE polling behavior control

Related to cloudflare/agents#752

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
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