Figma remote MCP fails with "-32601 Method not found" in 1.1.21 (works in 1.1.9)

Summary

After updating the GitHub Copilot desktop app to 1.1.21 (macOS, arm64), the Figma remote MCP server
(https://mcp.figma.com/mcp, type http, OAuth) connects, completes OAuth, and is then dropped with
MCP error -32601: Method not found. The same mcp-config.json, OAuth registration and keychain token
work in app 1.1.9.

The difference is the bundled Copilot CLI runtime (the app logs source=Bundled for it at startup):

Figma's server accepts protocol revision 2026-07-28 in the handshake but does not implement the new
methods that revision requires (server/discover, subscriptions/listen), so the runtime's first call
after initialize fails. The 1.0.79-9 runtime negotiated 2025-11-25 and worked; 1.0.84-5 treats the
failure as fatal instead of falling back to 2025-11-25.

This matches the Copilot CLI 1.0.81 changelog entry "Ship MCP 2026-07-28 support to CLI, SDK, IDE, and
in-memory clients" (2026-08-27). Standalone CLI builds from 1.0.81 onward show the same behaviour, so
the fix most likely belongs in the shared runtime rather than the app. Related reports:
github/copilot-cli#4370 (aborts on server/discover errors), github/copilot-cli#4834 (2026-07-28
support incomplete), kjgpta/vectorsmith#28 (handshake change starting at CLI 1.0.81), and
github/app#1682 (earlier Figma remote MCP failures from the desktop app).

Steps to reproduce

1. Install GitHub Copilot app 1.1.21 on macOS.
2. ~/.copilot/mcp-config.json:

   { "mcpServers": { "figma": { "type": "http", "url": "https://mcp.figma.com/mcp", "tools": ["*"] } } }
   

3. Open the app, complete the Figma OAuth flow when prompted.
4. Observe the Figma server shows as failed and no Figma tools are available.

Expected

Figma tools are available, as in 1.1.9.

Logs (~/.copilot/logs/process-*.log)

1.1.21 / runtime 1.0.84-5:

[INFO] [rust:rmcp::service] Service initialized as client {"peer_info":"Some(ServerPeerInfo { protocol_version: ProtocolVersion(\"2026-07-28\"), ... server_info: Some(Implementation { name: \"Figma MCP Server\", version: \"1.0.0\" ...
[WARNING] [rust:copilot_runtime::session::mcp::agent_host] MCP error -32601: Method not found. {"server":"figma"}
[ERROR] [rust:mcp_engine::session_authorizer] OAuth succeeded but MCP server reconnect failed {"server_name":"figma","error":"MCP error -32601: Method not found."}

Also seen intermittently during re-auth attempts on 1.1.21:

[ERROR] ... github_app::handlers::mcp_config: failed to start MCP OAuth login error=RPC error -32603: Request session.mcp.oauth.login failed with message: Client registration failed: server responded with status 403 Forbidden server_name=figma

1.1.9 / runtime 1.0.79-9 (same machine, same config, same token):

[INFO] [rust:rmcp::service] Service initialized as client {"peer_info":"Some(ServerPeerInfo { protocol_version: ProtocolVersion(\"2025-11-25\"), ... server_info: Some(Implementation { name: \"Figma MCP Server\", version: \"1.0.0\" ...

(no error follows; tools load)

Environment

• GitHub Copilot app 1.1.21; works on 1.1.9
• macOS 26 (Darwin 25.6.0), Apple Silicon
• Figma remote MCP server, OAuth via dynamic client registration
• The GitHub remote MCP server (github-mcp-server) connects fine on 1.1.21 with the same 2026-07-28 negotiation, so the problem is specific to servers that advertise the new revision without implementing all of it

Notes

• COPILOT_CLI_PATH is ignored in shipped builds, so the runtime cannot be swapped to test a fix.
• Suggested fix: when a server negotiates 2026-07-28 but answers -32601 to a mandatory new-revision
  method, reconnect using 2025-11-25 rather than failing the server.

Start with the bundled Copilot CLI runtime and the MCP session path shown in the app logs, using the provided mcp-config.json and Figma OAuth setup to reproduce the failure. Compare protocol negotiation and the first request after initialize with runtimes 1.0.79-9 and 1.0.84-5, then verify that compatible Figma tools load without the -32601 error while the GitHub remote MCP server still works.