feat: Update isolateTrace implementation to use startNewTrace

Update withMonitor to use startNewTrace() instead of startSpan() when
isolateTrace is enabled, following PR feedback to only isolate traces
without creating spans.

Author: naaa760

packages/core/src/exports.ts

@@ -15,7 +15,7 @@ import { isThenable } from './utils/is';
 import { uuid4 } from './utils/misc';
 import type { ExclusiveEventHintOrCaptureContext } from './utils/prepareEvent';
 import { parseEventHintOrCaptureContext } from './utils/prepareEvent';
-import { startSpan } from './tracing/trace';
+import { startNewTrace } from './tracing/trace';
 import { timestampInSeconds } from './utils/time';
 import { GLOBAL_OBJ } from './utils/worldwide';
 
@@ -170,38 +170,31 @@ export function withMonitor<T>(
   return withIsolationScope(() => {
     // If isolateTrace is enabled, start a new trace for this monitor execution
     if (upsertMonitorConfig?.isolateTrace) {
-      return startSpan(
-        {
-          name: `monitor.${monitorSlug}`,
-          op: 'monitor',
-          forceTransaction: true,
-        },
-        () => {
-          let maybePromiseResult: T;
-          try {
-            maybePromiseResult = callback();
-          } catch (e) {
-            finishCheckIn('error');
-            throw e;
-          }
-
-          if (isThenable(maybePromiseResult)) {
-            return maybePromiseResult.then(
-              r => {
-                finishCheckIn('ok');
-                return r;
-              },
-              e => {
-                finishCheckIn('error');
-                throw e;
-              },
-            ) as T;
-          }
-          finishCheckIn('ok');
-
-          return maybePromiseResult;
-        },
-      );
+      return startNewTrace(() => {
+        let maybePromiseResult: T;
+        try {
+          maybePromiseResult = callback();
+        } catch (e) {
+          finishCheckIn('error');
+          throw e;
+        }
+
+        if (isThenable(maybePromiseResult)) {
+          return maybePromiseResult.then(
+            r => {
+              finishCheckIn('ok');
+              return r;
+            },
+            e => {
+              finishCheckIn('error');
+              throw e;
+            },
+          ) as T;
+        }
+        finishCheckIn('ok');
+
+        return maybePromiseResult;
+      });
     }
 
     // Default behavior without isolateTrace

packages/core/test/lib/client.test.ts

@@ -11,6 +11,7 @@ import {
   SyncPromise,
   withMonitor,
 } from '../../src';
+import { startNewTrace } from '../../src/tracing';
 import * as integrationModule from '../../src/integration';
 import { _INTERNAL_captureLog } from '../../src/logs/internal';
 import { _INTERNAL_captureMetric } from '../../src/metrics/internal';