[plan] Implement standardized MCP error codes

[github-actions]

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