MCP: subscriptions/listen request missing protocol version header breaks GitHub MCP connection

[pshickeydev]

Description

Description

After upgrading to v0.87.0, the GitHub MCP server (https://api.githubcopilot.com/mcp/) reports an error during
initialization. Tool listing succeeds, but a subsequent subscriptions/listen request is rejected because it does not
include the Mcp-Protocol-Version header that the server requires.

Error

connection closed: calling "tools/list": client is closing: sending "subscriptions/listen": Mcp-Protocol-Version header
is required for requests carrying "io.modelcontextprotocol/protocolVersion": Bad Request

Configuration

{
  "github": {
    "type": "http",
    "url": "https://api.githubcopilot.com/mcp/",
    "headers": {
      "Authorization": "Bearer $GITHUB_TOKEN"
    }
  }
}

Root Cause

After capability negotiation completes and tools/list succeeds, Crush sends a subscriptions/listen request that
includes the io.modelcontextprotocol/protocolVersion field in the request body but does not include the corresponding
Mcp-Protocol-Version HTTP header. GitHub's MCP endpoint enforces that any request carrying the protocol version field
must also include the header, and returns 400 Bad Request when it is missing.

The connection teardown caused by this error cascades back through tools/list , which is why the error message appears
to originate from tools/list even though that call had already succeeded.

Expected Behavior

Crush should include the Mcp-Protocol-Version header on all HTTP requests sent after protocol version negotiation is
complete, including subscriptions/listen and any other post-initialization requests.

Environment

• Crush version: v0.87.0
• MCP server: GitHub Copilot ( https://api.githubcopilot.com/mcp/ )
• OS: Linux

Additional Context

• There is a related spec-level discussion about protocol version header semantics: https://github.
com/modelcontextprotocol/modelcontextprotocol/issues/854
• The MCP 2025-06-18 spec states that if a server does not receive the header it should assume a fallback version, but
GitHub's implementation requires it unconditionally when the protocol version field is present in the request body.
• Despite the error status, MCP tools from GitHub may still be partially functional in some sessions since tools are
listed before the failure occurs.

Version

0.87.0

Environment

No response

[jan-xyz]

The fix is already merged in the go-sdk (modelcontextprotocol/go-sdk#1107) but isn't released yet. You can fix it by compiling crush from source and pinning it to the fix with

go mod edit -replace github.com/modelcontextprotocol/go-sdk=github.com/modelcontextprotocol/go-
sdk@2781b8f7e35bb7d064d44dd2193d7d77179b8630
go mod tidy
go install .

@taciturnaxolotl should this maybe get pinned in the repo until the fix is released?

[taciturnaxolotl]

yeah thats a good idea; hold on

[pshickeydev]

I also acknowledge this might just be me needing to set up a pre-registered client as an alternative, which I haven't done yet. https://github.com/charmbracelet/crush#pre-registered-clients

[taciturnaxolotl]

you do unfortunately need a pre registered client for github because they are annoying and don't support dcr as far as i know but this is also an issue with them

[jan-xyz]

if you have gh cli installed and oauth configured, then you can just do

    "github": {
      "type": "http",
      "url": "https://api.githubcopilot.com/mcp/",
      "headers": {
        "Authorization": "Bearer $(gh auth token)"
      }
    }

[taciturnaxolotl]

oooh even better!