Implement standardized MCP error codes using jsonrpc.Error

[Copilot]

MCP server tool handlers returned generic errors wrapped in mcp.CallToolResult. This prevented MCP clients from distinguishing between parameter validation errors and internal failures.

Changes

Error Infrastructure

• Added mcpErrorData() helper to marshal error context to json.RawMessage
• Replaced CallToolResult error returns with jsonrpc.Error using standard codes

Error Classification

• InvalidParams (-32602): Missing required parameters, conflicting flags, invalid jq filters
• InternalError (-32603): Command execution failures, Docker preparation, context cancellation

Error Context

• Structured Data field includes error details, command output, and user-provided input for debugging
• Error messages are clear and actionable
• Context includes error messages, output, filter expressions, and run IDs

Example

Before:

return &mcp.CallToolResult{
    Content: []mcp.Content{
        &mcp.TextContent{Text: fmt.Sprintf("Error: %v\nOutput: %s", err, output)},
    },
}, nil, nil

After:

return nil, nil, &jsonrpc.Error{
    Code:    jsonrpc.CodeInternalError,
    Message: "failed to compile workflows",
    Data:    mcpErrorData(map[string]any{"error": err.Error(), "output": string(output)}),
}

Parameter validation with context:

return nil, nil, &jsonrpc.Error{
    Code:    jsonrpc.CodeInvalidParams,
    Message: "invalid jq filter expression",
    Data:    mcpErrorData(map[string]any{"error": jqErr.Error(), "filter": args.JqFilter}),
}

Testing

Added mcp_server_error_codes_test.go with integration tests covering:

• Parameter validation failures
• Internal execution failures
• Error message propagation through MCP SDK

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[plan] Implement standardized MCP error codes</issue_title>
<issue_description>## Objective

Update tool error handling to use standardized MCP error codes from v1.2.0's jsonrpc.Error constants for better client compatibility.

Context

v1.2.0 exposes standardized error codes via jsonrpc.Error sentinels. Currently, tools return generic errors. Using standardized codes enables MCP clients to handle errors more intelligently.

Approach

1. Review current error handling in tool handlers in pkg/cli/mcp_server.go
2. Identify error types (invalid params, internal error, method not found, etc.)
3. Replace generic errors with jsonrpc.Error constants:

   // Example
   return nil, jsonrpc.NewError(jsonrpc.InvalidParams, "workflow not found", nil)

4. Update error messages to be clear and actionable
5. Add tests for error scenarios

Files to Modify

• pkg/cli/mcp_server.go - Update error returns in tool handlers
• pkg/cli/mcp_server_test.go - Add tests for error codes

Acceptance Criteria

• All tool handlers use appropriate jsonrpc.Error codes
• Error messages are clear and actionable
• Tests verify correct error codes are returned
• Error handling follows MCP best practices
  Related to [plan] Upgrade MCP Go SDK to v1.2.0 and implement improvements #7711

AI generated by Plan Command for discussion #7710

Comments on the Issue (you are @copilot in this section)

• Fixes [plan] Implement standardized MCP error codes #7714

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[pelikhan]

@copilot you cannot leak internal error data for security reasons.

[Copilot]

Fixed in 7c8a907. Removed internal error data from all error responses:

• No command output exposed
• No internal error messages exposed
• Only user-provided input (jq filters, run_id) included in Data field

All error code tests still passing.

[pelikhan]

@copilot revert last commit

[Copilot]

@copilot revert last commit

Reverted in 754db11. The security fix has been undone and internal error data (command output, error messages) is now included in error responses again.