Add a Suitelet to a Custom Tab Using a User Event Script

/**
 * @NApiVersion 2.x
 * @NScriptType UserEventScript
 */
define(['N/record', 'N/runtime', 'N/ui/serverWidget', 'N/url'], 
function(record, runtime, serverWidget, url) {
    function beforeLoad(scriptContext) {
        var currentUserID = runtime.getCurrentUser().id;

        // Only apply on Edit or View from UI
        if ((runtime.executionContext === runtime.ContextType.USER_INTERFACE) &&
            (scriptContext.type === scriptContext.UserEventType.EDIT || 
             scriptContext.type === scriptContext.UserEventType.VIEW)) {

            // 1. Add a new Tab
            var customTab = scriptContext.form.addTab({
                id: 'custpage_sample_tab',
                label: 'Sample Tab'
            });

            // 2. Add a clickable HTML link to Suitelet on the tab
            var linkField = scriptContext.form.addField({
                id: 'custpage_new_req_link',
                type: serverWidget.FieldType.INLINEHTML,
                label: ' ',
                container: 'custpage_sample_tab'
            });

            // 3. Build the URL for the Suitelet dynamically
            var linkURL = url.resolveScript({
                scriptId: 'customscriptsuiteletsample_yourfirstsamp', // Replace with your actual script ID
                deploymentId: 'customdeploysuiteletsample_yourfirstsamp'
            }) + '&recordid=' + scriptContext.newRecord.id;

            linkField.defaultValue = '<b>Click <a href="' + linkURL + 
                '">here</a> to create a new document signature request record.</b>';

            // 4. Optional: Add a custom sublist to the same tab
            var sigSublist = scriptContext.form.addSublist({
                id: 'custpage_sig_req_sublist',
                type: serverWidget.SublistType.LIST,
                label: 'Document Signature Requests',
                tab: 'custpage_sample_tab'
            });

            sigSublist.addField({ id: 'custpage_req_name', type: serverWidget.FieldType.TEXT, label: 'Name' });
            sigSublist.addField({ id: 'custpage_req_status', type: serverWidget.FieldType.TEXT, label: 'Status' });
            sigSublist.addField({ id: 'custpage_req_created', type: serverWidget.FieldType.DATE, label: 'Date Created' });

            // NOTE: You can populate the sublist dynamically via Suitelet or Client Script
        }
    }

    return {
        beforeLoad: beforeLoad,
    };
});