Describe the bug
Copilot CLI 1.0.79-1 cannot connect to an MCP server built with FastMCP.
Before MCP initialization completes, the CLI sends a server/discover request. FastMCP does not implement this method and returns -32602 Invalid request parameters. Copilot treats that response as a fatal lifecycle negotiation error and aborts initialization.
The same server and configuration work without issue in Copilot CLI 1.0.78.
Affected version
1.0.79-1
Steps to reproduce the behavior
- Configure the MCP server as shown in "Additional Context".
- Start Copilot CLI 1.0.79-1.
- Observe the CLI sending
server/discover.
- FastMCP rejects the unsupported request.
- Copilot aborts MCP lifecycle negotiation before
initialize completes.
Expected behavior
An unsupported optional server/discover request should not block normal MCP initialization.
If the server returns an error for the probe, Copilot should continue with the standard initialize lifecycle rather than treating the response as fatal.
In particular, this should not depend on the server returning exactly -32601 Method not found. FastMCP currently returns -32602 because the request does not match any supported ClientRequest schema.
Additional context
MCP configuration
Values have been redacted:
{
"mcpServers": {
"fabric-rti-mcp": {
"command": "uvx",
"args": ["microsoft-fabric-rti-mcp"],
"env": {
"KUSTO_SERVICE_URI": "<redacted>",
"KUSTO_SERVICE_DEFAULT_DB": "<redacted>",
"FABRIC_API_BASE": "<redacted>"
}
}
}
}More Details
Another MCP implementation returns:
Method 'server/discover' is not available.
Copilot tolerates that response and continues initialization.
Describe the bug
Copilot CLI 1.0.79-1 cannot connect to an MCP server built with FastMCP.
Before MCP initialization completes, the CLI sends a
server/discoverrequest. FastMCP does not implement this method and returns-32602 Invalid request parameters. Copilot treats that response as a fatal lifecycle negotiation error and aborts initialization.The same server and configuration work without issue in Copilot CLI 1.0.78.
Affected version
1.0.79-1
Steps to reproduce the behavior
server/discover.initializecompletes.Expected behavior
An unsupported optional
server/discoverrequest should not block normal MCP initialization.If the server returns an error for the probe, Copilot should continue with the standard
initializelifecycle rather than treating the response as fatal.In particular, this should not depend on the server returning exactly
-32601 Method not found. FastMCP currently returns-32602because the request does not match any supportedClientRequestschema.Additional context
MCP configuration
Values have been redacted:
{ "mcpServers": { "fabric-rti-mcp": { "command": "uvx", "args": ["microsoft-fabric-rti-mcp"], "env": { "KUSTO_SERVICE_URI": "<redacted>", "KUSTO_SERVICE_DEFAULT_DB": "<redacted>", "FABRIC_API_BASE": "<redacted>" } } } }More Details
Another MCP implementation returns:
Copilot tolerates that response and continues initialization.